Propagation Sample Lesson

RHS Level 2 Certificate in Horticulture Study Notes – Lesson Three

Plant Propagation

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Seedlings of Begonia sp. grown in module tray

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CONTENTS

ILLUSTRATIONS...................................................................................................... 5

INTRODUCTION....................................................................................................... 7

TWO LONGER QUESTIONS.................................................................................... 8

EIGHT SHORT ANSWER QUESTIONS ................................................................... 9

1 PROPAGATION METHODS............................................................................... 10 Definitions of Propagation.................................................................................... 10

Seed Propagation ................................................................................................ 11 When to Propagate By Seed............................................................................ 12 Properties of SeedPropagated Plants ............................................................. 13 Benefits of Seed Propagation........................................................................... 13 Limitations of Seed Propagation....................................................................... 14

Vegetative Propagation........................................................................................ 16 When to Propagate Vegetatively ...................................................................... 16 Properties of VegetativelyPropagated Plants .................................................. 17 Benefits of Vegetative Propagation .................................................................. 17 Limitations of Vegetative Propagation .............................................................. 18

Micropropagation ................................................................................................. 19

Genetically Modified Crops .................................................................................. 20

Seed Versus Vegetative Propagation .................................................................. 21 Example: Drumstick Primrose .......................................................................... 21 Example: Chinese Wisteria .............................................................................. 22 Example: Rhubarb ........................................................................................... 23 Example: Petunia ............................................................................................. 23 Example: Annual Sunflower ............................................................................. 24

2 SEED PROPAGATION....................................................................................... 26 Introduction.......................................................................................................... 26

Seed Dormancy................................................................................................... 26 Innate Dormancy.............................................................................................. 28 Induced Dormancy ........................................................................................... 28 Enforced Dormancy.......................................................................................... 28 Dormancy Mechanisms.................................................................................... 29 Exogenous Dormancy................................................................................... 29 Physical Dormancy.................................................................................... 29 Chemical Dormancy.................................................................................. 30 Mechanical Dormancy............................................................................... 30

Endogenous Dormancy ................................................................................ 30 Physiological Dormancy ............................................................................ 31 Morphological Dormancy........................................................................... 31 Morphophysiological Dormancy................................................................. 32

Double and Multiple Dormancy..................................................................... 32

Treatments to Overcome Dormancy .................................................................... 33 Scarification ..................................................................................................... 33


Stratification ..................................................................................................... 35 Examples of Seed Treatment to Overcome Dormancy..................................... 37

External Environmental Factors Affecting Germination ........................................ 39 Water ............................................................................................................... 39 Gases............................................................................................................... 40 Temperature..................................................................................................... 41 Light ................................................................................................................. 41

Seed Harvesting and Collection........................................................................... 42 Seeds of Woody Perennials ............................................................................. 42 Seeds of Herbaceous Perennials, Biennials and Annuals ................................ 43 Case Study of Primula japonica .................................................................... 44

Seed Storage....................................................................................................... 47

Treatments .......................................................................................................... 48 Seed Priming.................................................................................................... 48 Pelleting Seed.................................................................................................. 49 Seed Dusting and Coating................................................................................ 50 Other Seed Treatments.................................................................................... 50

Dampingoff ......................................................................................................... 51 Symptoms of Dampingoff ................................................................................ 52 Control of Dampingoff Diseases...................................................................... 52

Successful Seed Germination in a Protected Environment .................................. 53 SeedStarting Media......................................................................................... 53 Composts ..................................................................................................... 54 Loam Composts ........................................................................................ 55 Loamless Compost.................................................................................... 56 Peatless Composts ................................................................................... 56

Seed Starting Pellets .................................................................................... 57 Containers for Seed Sowing............................................................................. 57

Sowing and Aftercare of Seeds Sown In Containers............................................ 59 When to Sow.................................................................................................... 59 How to Sow Seeds........................................................................................... 60 Sowing Seeds of Hardy Plants...................................................................... 62

Pricking Out and Potting Up ............................................................................. 63 Potting Composts ......................................................................................... 63 Pricking Out and Potting Up Procedure ........................................................ 64 Hardening Off ............................................................................................... 66

Germinating Seeds in the Open........................................................................... 67 Broadcast Seeding........................................................................................... 68 Sowing Seed in Drills ....................................................................................... 68 Thinning Seedlings........................................................................................... 70

3 FACTORS INFLUENCING PROPAGATION BY CUTTINGS.............................. 72 Introduction.......................................................................................................... 72

The Physiology of Propagation by Cuttings.......................................................... 73 Cutting Anatomy............................................................................................... 73 Callus............................................................................................................... 74 Physiology of Root Initiation ............................................................................. 75 Auxin ............................................................................................................ 76 Cytokinin....................................................................................................... 77 Gibberellins................................................................................................... 78


Abscissic Acid (ABA) .................................................................................... 78 Ethylene........................................................................................................ 78

Selection of Cutting Material ................................................................................ 78 Genetic Potential.............................................................................................. 79 Juvenility .......................................................................................................... 80 Nutritional Status of Cutting.............................................................................. 80 Health of Cutting Material................................................................................. 81 Timing .............................................................................................................. 81 Etioliation ......................................................................................................... 82 Temperature Manipulation of Stock Plant......................................................... 83

Treatment of Cutting Material............................................................................... 83

Environmental Factors Which Affect Rooting of Cuttings ..................................... 85 Temperature..................................................................................................... 85 Moisture ........................................................................................................... 86 Light ................................................................................................................. 87 Fertilisation....................................................................................................... 88 Establishment of a New Plant........................................................................... 89

4 VEGETATIVE PROPAGATION TECHNIQUES .................................................. 90 Introduction.......................................................................................................... 90

Cuttings ............................................................................................................... 90 Advantages of Propagation By Cuttings ........................................................... 91 Disadvantages of Propagation By Cuttings ...................................................... 91 Stem Cuttings................................................................................................... 92 Softwood Cuttings......................................................................................... 94 Greenwood Cuttings ..................................................................................... 98 SemiRipe Wood Cuttings ......................................................................... 98

Hardwood Cuttings ..................................................................................... 100 Deciduous Hardwoods ............................................................................ 101 Evergreen Hardwoods............................................................................. 105

Leaf Cuttings.................................................................................................. 106 Root Cuttings ................................................................................................. 109 Equipment for Propagation by Cuttings .......................................................... 111 Heated Propagation Units........................................................................... 111 Mist............................................................................................................. 113 Rooting Media............................................................................................. 114

Aftercare For Plants Produced By Cuttings .................................................... 114

Layering............................................................................................................. 114 Tip Layering ................................................................................................... 116 Simple Layering ............................................................................................. 117 Serpentine or Compound Layering................................................................. 119 Stooling or Mound Layering............................................................................ 119 Air Layering.................................................................................................... 121

Plant Division..................................................................................................... 122 Division of Offsets .......................................................................................... 123 Case Study of Offset Division: Primula auricula .......................................... 124

Division of Crowns.......................................................................................... 127 Division of Suckers......................................................................................... 127 Division of Bulbs, Rhizomes and Tuberous Roots .......................................... 128

Budding and Grafting......................................................................................... 130


5 BUDDING AND GRAFTING ............................................................................. 131 Introduction........................................................................................................ 131 Scion.............................................................................................................. 131 Stock or Rootstock ......................................................................................... 131 Grafting and Budding ..................................................................................... 132

Why Graft and Bud? .......................................................................................... 132

The Limitations of Grafting and Budding ............................................................ 135

Graft Incompatibility ........................................................................................... 135

Tools and Materials ........................................................................................... 136

Formation of the Graft Union.............................................................................. 138 How Graft Unions Form.................................................................................. 138 How TBudding Unions Form ......................................................................... 139 Essential Conditions For Successful Graft Unions.......................................... 139

Grafting Techniques .......................................................................................... 140 Whip and Tongue Graft .................................................................................. 140 Budding.......................................................................................................... 142

Care of Grafted Plants ....................................................................................... 145

6 SAFE, HEALTHY AND ENVIRONMENTALLY SUSTAINABLE PRACTICES.. 146 Health and Safety .............................................................................................. 146

Environmentally Sustainable Practices .............................................................. 147

DEVELOPMENT OF A PROJECT FOLDER ........................................................ 148


ILLUSTRATIONS

Figure 1 Small Domestic Glasshouse Packed With Plants.................................... 7 Figure 2 Selective Breeding Has Produced the Many Cultivars of Rose (Rosa) ..... 11 Figure 3 Commercial Production of Viola (Viola cornuta 'Sorbet Coconut Duet’) .... 14 Figure 4 Vegetative Propagation of Garlic (Allium sativum) via Bulblets ................. 16 Figure 5 Daylily Hemerocallis sp. ........................................................................ 18 Figure 6 Orchid Seedlings Germinated Using Micropropagation Techniques ......... 20 Figure 7 Orchid Seedlings Ready for Potting Up .................................................... 20 Figure 8 Wisteria sinensis Cultivar.......................................................................... 22 Figure 9 SeedPropagated Petunia ........................................................................ 24 Figure 10 Fruits/Seeds of Annual Sunflower........................................................... 25 Figure 11 Paeonia Flowers..................................................................................... 27 Figure 12 Cranesbill (Geranium sp.)....................................................................... 30 Figure 13 Davidia involucrata Ready for Warm Storage ......................................... 32 Figure 14 Scarification of Seeds............................................................................. 34 Figure 15 Seed Stratification .................................................................................. 36 Figure 16 Seed Stratification for the Home Gardener ............................................. 37 Figure 17 Watering from Below .............................................................................. 40 Figure 18 Collecting Seed from Cotoneaster spp. .................................................. 42 Figure 19 Seed Capsule of Nigella damascena ...................................................... 43 Figure 20 Seeds of Poppy (Papaver sp.)................................................................ 44 Figure 21 Primula japonica Flowers in May ............................................................ 44 Figure 22 Seed Pods of Primula japonica............................................................... 44 Figure 23 Collected Seed Pods of Primula japonica ............................................... 45 Figure 24 Seed Cleaning........................................................................................ 45 Figure 25 Glassine Seed Packets .......................................................................... 46 Figure 26 Refrigerated Seed Storage..................................................................... 46 Figure 27 Chitted Seeds......................................................................................... 48 Figure 28 Pelleted Seed of Begonia sp. ................................................................. 49 Figure 29 Damping Off ........................................................................................... 52 Figure 30 A Small Sample of Perlite....................................................................... 55 Figure 31 A Small Sample of Vermiculite................................................................ 55 Figure 32 PeatBased Jiffy 7 .................................................................................. 57 Figure 33 Degradable Containers For Seed Starting .............................................. 58 Figure 34 Module Tray ........................................................................................... 58 Figure 35 Label Writing .......................................................................................... 61 Figure 36 Methods of Seed Sowing Sowing in Pans or Pots ............................... 61 Figure 37 Methods of Sowing – Hardy Perennial seed ........................................... 62 Figure 38 Seedlings of Primula reidii var. williamsii Grown in Modular Tray............ 63 Figure 39 Widgers and Dibbers.............................................................................. 65 Figure 40 Seedling Ready to Transplant ................................................................ 65 Figure 41 Drill For Sowing Seeds ........................................................................... 69 Figure 42 Cross Section of Young Deadnettle Stem............................................... 75 Figure 43 Rooting Hormone Visible on Bottom of Cutting....................................... 77 Figure 44 Spacing of Nodes ................................................................................... 79 Figure 45 Leaves Suitable for Leaf Cuttings........................................................... 82 Figure 46 Wounding of Cuttings ............................................................................. 84 Figure 47 An Inexpensive Home Propagation Unit ................................................. 87 Figure 48 Lining Out of Rooted Cuttings or Layers ................................................. 89 Figure 49 Longitudinal Section of Nodal Cutting Base............................................ 93 Figure 50 Internodal cutting of Hydrangea macrophylla.......................................... 94 Figure 51 Softwood Stem Cuttings (e.g. Weigela Bristol Ruby)................................ 95


Figure 52 A Rooted Greenwood Cutting of Daphne cneorum (Garland flower)....... 97 Figure 53 Leaf Bud Cutting (Ficus elastica) ............................................................ 99 Figure 54 A System for the Amateur..................................................................... 100 Figure 55 Stock Plants Used to Supply Cutting Material....................................... 101 Figure 56 The Traditional Deciduous Hardwood Stem Cuttings of Ribus nigrum,

Black Currant ................................................................................................. 102 Figure 57 Cutting for a Bush Grown on a "Leg" .................................................... 104 Figure 58 A Mallet Cutting of Berberis stenophylla ............................................... 104 Figure 59 Vine Eye Cutting................................................................................... 104 Figure 60 Professional Environment for Rooting Evergreen Hardwood Cuttings .. 105 Figure 61 Broadleaf Evergreen Hardwood Cutting ............................................... 106 Figure 62 African Violet Leaf Petiole Cutting ........................................................ 107 Figure 63 Cuttings That May be Taken From a Streptocarpus Leaf...................... 108 Figure 64 Scaling Lily Bulbs ................................................................................. 109 Figure 65 Root Cutting ......................................................................................... 111 Figure 66 A Heated Bench for Propagation of Cuttings ........................................ 112 Figure 67 Heated Propagation Unit ...................................................................... 112 Figure 68 A Modified Garner Bin .......................................................................... 113 Figure 69 Tip Layers ............................................................................................ 116 Figure 70 Simple Layering.................................................................................... 117 Figure 71 Cutting to Form a Tongue..................................................................... 118 Figure 72 Serpentine Layering ............................................................................. 119 Figure 73 Mound Layering.................................................................................... 120 Figure 74 Air Layering of Scindapsus aureus ....................................................... 122 Figure 75 Parent Auricula With Offsets................................................................. 124 Figure 76 Separated Offsets and Parent Plant ..................................................... 125 Figure 77 Pottedup Offset ................................................................................... 125 Figure 78 Growing on Auriculas ........................................................................... 126 Figure 79 Segment of Bergenia Rhizome That Will be Used to Generate a New

Plant............................................................................................................... 129 Figure 80 Example of a Graft................................................................................ 132 Figure 81 A Grafted Apple Tree............................................................................ 133 Figure 82 A Compatible Graft Union with Different Growth Rates......................... 136 Figure 83 Budding and Grafting Knives ................................................................ 137 Figure 84 Graft Union........................................................................................... 138 Figure 85 Preparing the Rootstock ....................................................................... 141 Figure 86 Scion Preparations ............................................................................... 141 Figure 87 Joining Stock and Scion Wood ............................................................. 142 Figure 88 The "T" Cut on the Rootstock ............................................................... 143 Figure 89 The Bud Shield...................................................................................... 144 Figure 90 Insert Bud in the Rootstock................................................................... 144


INTRODUCTION

Plant propagation can be one of the most satisfying aspects of gardening. It requires considerable knowledge of plants and how they naturally reproduce themselves.

There is also a high degree of craftsmanship involved through which both young and older gardeners can develop their skills. It gives one the opportunity to both handle plants and see them at close quarters.

Many believe there is nothing more rewarding than to raise their own plants from seeds and cuttings. Even in a very small glasshouse many hundreds of plants can be raised with considerable financial saving. Excess plants can be given to friends or swapped for something else. Plant sales can be organised at local school fairs.

Figure 1 Small Domestic Glasshouse Packed With Plants

This lesson will focus on the principles and main practices involved in plant propagation. The lesson will commence with propagation via sexual means (that is, using seeds to produce new plants) and then will address propagation via asexal methods (using cuttings, offsets and other vegetative parts of the plant to make new plants). At the end of the lesson there will be an introduction to budding and grafting techniques. Finally, there is a brief overview of the health and safety concerns involved with the propagation process and some environmentally friendly issues.

The focus of this lesson will be propagation in a garden situation, however some mention of commercial propagation will sometimes be made.


TWO LONGER QUESTIONS

Please answer both of these longer questions:

QUESTION ONE (a) Define the terms physical and physiological dormancy of

seeds. (4 marks)

(b) Describe one method for overcoming a named physical and a named physiological dormancy mechanism in seeds.

(2 marks)

(c) State the essential conditions for the successful seed germination of viable seeds.

(4 marks)

(d) Describe how conditions for successful germination can be met in a protected environment for a named halfhardy annual.

(5 marks)

(e) Describe how the conditions for successful germination can be met in the open for a named hardy annual.

(5 marks)

QUESTION TWO (a) Define the term “vegetative propagation” and give four

examples of different types of vegetative propagation. (4 marks)

(b) Describe the propagation of plants by division and give two named examples of suitable plants.

(8 marks)

(c) Explain how plant stress can be reduced when leafy cuttings are placed into a suitable environment to form roots.

(4 marks)

(d) Explain the process of “weaning” of rooted cuttings and explain the reasons why “weaning” of rooted cuttings may be valuable.

(4 marks)


EIGHT SHORT ANSWER QUESTIONS

Answer all the short answer questions, confining your answers to a few lines only.

Short answer questions are worth 5 marks each.

1. (a) Give one advantage of raising plants from seeds.

(b) Give three advantages of obtaining seed commercially.

2. What is (a) stratification and (b) scarification of seeds?

3. (a) Name three types of graft.

(b) Name the rootstocks used for plum.

4. State briefly how you would propagate the following plants: Cissus antarctica, Ficus elastica decora, Aphelandra squarrosa.

5. Vegetative (asexual) propagation has advantages and limitations when compared with sexual propagation. State two of these advantages and two of the limitations.

6. Distinguish between ‘leaf cuttings’* and ‘leaf petiole cuttings’. Give one example of a suitable genus that can be propagated by each method.

7. Why does the use of ‘bottom heat’ promote rooting in cuttings?

8. List five factors to consider when selecting plant material for taking cuttings.

*Leaves are remarkable in a range of ways. Some leaves will proliferate, some root from their petioles. Others may root from the leaf blade – the lamina yet others may root from the leaf with the leaf bud.

For this question please assume that the term “leaf cuttings” refers to cuttings which are the leaf blade.


1 PROPAGATION METHODS

By the end of this section, you will be able to differentiate between the characteristics of plants produced by seed and plants produced by vegetative propagation methods:

• Define the terms seed propagation and vegetative propagation.

• Compare two characteristics of plants produced from seed as compared to those produced by vegetative methods.

• State the relative benefits and limitations of seed propagation and vegetative propagation.

Definitions of Propagation

Propagation is the method by which plants may be increased in number.

In the natural environment, the majority of plants reproduce through the production of seed (that is, via sexual methods). Sexual reproduction gives plants the advantage of genetic variation. This capacity for genetic change permits the plants to adapt to a changing environment and to grow in hostile areas. One reason for this is due to one of the qualities of seeds – most seeds have the ability to remain dormant when environmental conditions are not suitable for growth.

However, not all plants reproduce themselves exclusively by seeds. Some plants produce exact copies of themselves via vegetative or asexual methods. For example, many herbaceous perennials and bulbs produce offsets, each of which is genetically identical to the parent plant. Some woody plants (for example, the American Beech, Fagus grandifolia) produce colonies of clones – each genetically identical – through root suckers.

Vegetative or asexual reproduction is a way of reproducing quickly (faster than through seeds). This method, however, has one drawback – all plants produced are genetically identical to the parent. If environmental conditions change, the plant may not have the ability to adapt to the new conditions. All plants share the same qualities and weaknesses. For example, most elm trees (Ulmus procera) growing in Britain during the 1960s and 1970s were clones of a small group of plants and these were susceptible to Dutch Elm Disease. If more plants had a greater degree of genetic variation, perhaps some would have possessed an ability to withstand the effects of the disease.

However, all methods of plant propagation involve living material and for success to be achieved the needs of the tissues have to be met.


? Can you note down what these needs might be?

Check your answer at the end of this section.

Seed Propagation

Seed propagation is the production of new plants through the use of seeds.

The production of seeds involves the combination of genetic material from both the plant that contributes the ovule and the plant that contributes the pollen. As a result, seeds are the result of sexual reproduction ∗ . The processes that produce both the ovule and pollen and the process of pollination have been described in lesson 1.

Because seeds result from a combination of genetic information from two sources, for many centuries both gardeners and farmers have manipulated this to their advantage. The original wheat plant has been improved over thousands of years because higheryielding seedlings were selected by astute early farmers. The ability to produce variable offspring from sexually produced seed is a miracle of nature which gives huge benefit to plant adaptation. Plants can evolve to fit into an ever changing natural world.

Figure 2 Selective Breeding Has Produced the Many Cultivars of Rose (Rosa)

As a quick review of lesson 1 material, seeds are the result of meiotic cell division and thence sexual reproduction in flowering plants. A sexually produced seed gives rise to new combinations of the genetic material derived from both the male and female parent plants.

Some plant species have their male and female flowers on different plants (these are

∗ There is a situation, called apomixis, whereby seeds are produced via asexual methods. In some grasses (for instance the annual meadow grass, Poa annua) and a small number of other plants (dandelion, Taraxacum officinale) seed is produced without meiosis and fertilisation.


called dioecious plants) and this ensures that two individuals are involved in seed production. Holly (Ilex spp.) species provide a good example of this type – plants are either female (which produce attractive fruit during the autumn and winter) or male (which do not produce the attractive fruit, but are necessary for fruit formation on nearby female plants).

Having a grasp of what a species is helps in developing your knowledge of seed propagation. The species can be defined as “populations of plants which when they interbreed produce similar offspring”.

Wild populations of plant species do tend to breed true ∗∗ . The variation in the individual seedling may be minimal and may not be observable. However, in some natural populations the variation is considerable both in plant morphology (form) and “productivity”. These natural variations are the starting point for selective breeding. By choosing parent plants with some desirable quality (for example, better fruit or attractive flowers or disease resistance), a plant breeder may magnify the characteristic in offspring. The result of a breeding programme may be plants with more valuable characteristics than the original wild form. Most cultivated plants are the result of breeding programmes that have focused on improvement of wild plant forms.

When to Propagate By Seed

The vast majority of annual plants are seedpropagated. Most commercially available annuals are the result of decades of selection and breeding because they have desirable qualities and are easily propagated from seed.

Seed propagation is the method usually preferred under the following circumstances:

• Seed is readily obtained and inexpensive. • Seed can be sown immediately upon ripening or the seed is easy to store. • Seed has no difficulttobreak dormancy. • Large numbers of inexpensive plants are required (possibly to be used as

root stock). • The plant does not have a prolonged juvenile period (either delaying the

generation of seed or delaying the production of a saleable plant that is flowering).

• Plant breeding. Seed is the only way to combine the genetic material from one plant with the genetic material from another (whether within species or between species).

• Plant material is to be collected and transported large distances. • Plant material is to be saved for conservation purposes. • Maintenance of genetic diversity is desired. • The parent plant has a disease that would be carried forward to any plants

produced vegetatively.

∗∗ A plant “breeds true” when the offspring share the same desirable traits as the parent. Many hybrid plants do not “breed true” because the resulting offspring do not share the same desirable qualities of the parent.


Properties of SeedPropagated Plants

A plant grown from seed has the following qualities:

• The complete plant growth cycle is involved – from a juvenile period, through transition until the mature phase. This may include an undesirable, prolonged juvenile period for some plants.

• The genetic composition of the seedling (and eventually the plant) is usually different to that of the parent plants. The exception is for selfpollinated plants, where the same plant provides both male and female genetic material.

• The entire plant is composed of the same genetic material. Grafted plants (produced by asexual means) have some portion of the plant with one genetic composition and another portion of the plant with another genetic composition.

• The seedling is usually free of any diseases even through the parent plants may have been infected with some diseases (including viruses).

Some of these characteristics will be advantages while others will be a disadvantage.

Seedpropagated plants are the key to breeding programmes. For example, if the seed is the result of a breeding programme that is trying to produce a plant with both disease resistance and an attractive flower (and one parent has an attractive flower but is prone to disease, while the other parent has a lesser flower but disease resistance). Some of the offspring produced via sexual reproduction between these two parents may have all the qualities desired. Some (or perhaps all) of the offspring may not have the desired combination of traits. Only by growing the seeds that were produced via this cross to the flowering stage (or beyond) will these qualities be determined.

Asexual reproduction will produce identical copies of either one parent or the other and a combination of traits of the two plants cannot be produced without sexual production.

Benefits of Seed Propagation

1. Storage and Transport

Seeds are usually quite easy to store and can be transported easily. As a result, some seeds may be kept for a length of time before successful germination. This permits many seeds to be saved from year to year or for even longer for the purposes of plant conservation within seed banks.

2. Genetic Variability

Seedling variability can be an advantage enabling selection of better forms or permit the plant to withstand in a changing environment.

Plants grown by seed exhibit small genetic differences between plants (unlike clones that are vegetatively reproduced and have no genetic variation) and by


propagating by seed, this genetic diversity may be maintained.

The variability of a seed may be controlled through the use of carefullymade crosses.

The F1 hybrids are an example of this. F1 hybrids are the result of crosses between two deliberately established parental lines, each of which has minimal genetic variability within it (that is, the two parents are homozygous). As a result F1 hybrids have predictable, desirable qualities but their offspring (called the F2 generation) may not.

3. Seed Volume

Large numbers of plants may be grown at a very low cost.

Figure 3 Commercial Production of Viola (Viola cornuta 'Sorbet Coconut Duet’)

4. Pests and Diseases

Very few pests and / or disease organisms carry over in seed. As a result, new stock is potentially very healthy.

5. Hybrid Vigour

Many commercially available seeds are F1 hybrids which give healthy, uniform and early crops. They are also “true to type” and exhibit hybrid vigour.

6. Plant Breeding

Breeding programmes require the recombination of genetic material from the male and female plants. The only method to produce this is via seed production.

Limitations of Seed Propagation

1. Genetic Variability

This point was also listed as a benefit of seed propagation. However, there are two sides to variability. Many plants and most trees and shrubs are cross


pollinated, which brings about variable offspring.

Variability in nature allows the species to adapt to changes in the environment. However, for many cultivated plants, the unpredictable results from cross pollination are a disadvantage because offspring may be inferior to the parent plants. Variability may be especially disadvantageous in production of rootstocks for grafting purposes if the rootstock has a specific quality that is being exploited (for example, a dwarfing rootstock).

2. Loss of Desirable Characteristics

Poorer plants may result if seed is not selected from plants with desirable characteristics.

3. Seed Supply

Although the situation is improving, reliability of some seed supply is difficult.

In some plant groups (such as trees and shrubs) seeds may be difficult to obtain. Seed production varies from year to year in a number of plants – in some years, there is an abundant supply in others, a shortage. Many trees and shrubs bear abundant crops of seed every year, some every second or third year and others at longer intervals of up to ten years. During the intermittent years, small sporadic crops may occur.

4. Seed Dormancy

Some seeds have complex dormancy conditions to overcome. While dormancy is a quality exploited during seed storage, it may present a difficulty when it comes time to germinate the seed.

Breaking seed dormancy can only be achieved by having a full understanding of the factors involved. Frequently, dormant seeds require treatments lasting one or several months. Those seeds requiring multiple treatments (for example, a cool period followed by a warm period and then another cool period), may require more than a year before germination is completed.

5. Slower Propagation

Seed propagation may be a slower option for some subjects.

Propagation by seed may be a slow method of increase. This is an important consideration for both rare plants and for plants being propagated for sale. Plants must pass through the juvenile phase and reach maturity before bearing seeds – this may translate into a long wait for initial seed production.

Some plants, for example Wisteria spp. can be slow to mature from seed while plants grown from vegetative propagules may flower the second year after propagation. If the goal is to produce a flowering plant, clearly vegetative production is the better choice in this case.

Some plants, for example Trillium spp., may take several years to reach a saleable size when propagated by seed. Again, when growing commercially, the longer the time spent before the plant is saleable, the more the plant costs to grow. For the home gardener, this may be less of a concern.


Vegetative Propagation

Vegetative propagation involves the reproduction of plants using asexual (or nonsexual) methods. This means that vegetative plant parts (leaves, buds, shoots, and roots) not involved in sexual reproduction are used in the production of new plants.

The key to successful vegetative reproduction is the natural ability of plant tissues to produce adventitious roots or adventitious shoots or both. As a consequence, a portion of a plant may be used to produce an exact copy (genetically) of the original parent plant.

There are four primary means of vegetative propagation:

1. cuttings (including shoot, stem and root cuttings), 2. division 3. layering 4. budding and grafting (whereby portions of different plants are artificially joined

together to form a new plant).

Figure 4 Vegetative Propagation of Garlic (Allium sativum) via Bulblets

Vegetative propagation involves the production of clones. A clone is a genetically identical plant produced via vegetative techniques. Cloning in animals has had bad press but this practice has been used in horticulture for centuries. Most apple cultivars, for example, are clonal in origin.

When to Propagate Vegetatively

Vegetative propagation techniques are preferred in the following situations:

• The plant does not “come true” from seed. Vegetative propagation is widely used in horticulture because one is assured of the progeny being true to type. The colours, form, habit and desirability is maintained. The vegetative propagule develops by mitotic cell division carrying over the characteristics into the developing individual.

• The seed is not viable. • The seed is difficult to acquire or expensive. • The seed is difficult to store and cannot be sown immediately when ripe. • The seed has a dormancy that is very difficult or timeconsuming to break. • Seedproduced plants have an undesirable juvenile period or a long juvenile

period. • When the merits of one plant (for example, the fruiting qualities of a one

cultivar of apple) are to be combined with the attributes of another plant (for example, the dwarfing qualities of certain root stocks) and this cannot be

This is a drawing of a sprouted garlic clove that has been removed from the compost and placed on its side.


done via breeding programmes. In this situation, propagation via grafting is the suitable method.

Whilst all of the desirable features of a plant are perpetuated in vegetatively propagated plants, so too are any defects. The inability of some plants to flower well is carried over in the newly produced plant (this has been the case in some cultivars of Escallonia). Any susceptibility to disease may also be carried forward to the new plant. In addition, if the plant being propagated has a virus, then the offspring produced from this plant most likely has the virus also.

Properties of VegetativelyPropagated Plants

A plant propagated vegetatively has the following qualities:

• The plant is usually an exact copy of the parent, genetically. The newly produced plants will have the same qualities of form, leaf, flower, fruit, and diseaseresistance (to name a few). There are some minor exceptions to this. For example, some chimaeras are not successfully reproduced by all vegetative techniques.

• The plant has a shortened juvenile period, in most cases. The result is flower (and fruit) production earlier than a seedproduced plant, or the undesirable qualities of the juvenile period (for example, thorniness) may be skipped.

Benefits of Vegetative Propagation

The reasons for opting for vegetative propagation include the following:

1. Perpetuate Clone

Vegetative (or asexual) propagation is often the only way to perpetuate a clonal stock. This means that the desirable and recognisable characteristics of the clone will be preserved in the offspring. There will be minimal variation between offspring plants. Cultivars are true to type.

2. Nonviable Seeds

Plants such as figs and grapes that do not produce viable seeds can only have their numbers increased by vegetative propagation.

3. Reduced Juvenile Period

Often plants that are raised from seed go through a juvenile and transitional phase before maturity is reached. Undesirable features such as thorniness and the inability to produce flowers and fruit can be circumvented by the use of cuttings. Although cuttings are often taken using juvenile material from the parent, the duration of the juvenile period is often reduced dramatically when compared to seedpropagated plants. Once again, Wisteria spp. is an example of this.


4. Efficient Use of Material

Some techniques such as budding or leaf bud cuttings ensure efficient use of limited plant material. A large number of plants may be produced from a small amount of parent material. Vegetative micropropagation techniques may be able to use a very small amount of plant material to produce a large number of new plants.

5. Seed Dormancy

Difficulties with seed dormancy no longer pose a barrier to propagating new plants from existing ones.

6. Speed of Plant Production

Some vegetative techniques may produce plants very quickly – for example, division may be used to produce a number of new plants from an established daylilies (Hemerocallis sp.).

Figure 5 Daylily Hemerocallis sp.

Limitations of Vegetative Propagation

1. Diseases

Vegetatively propagated plants may be infected by disease that is present in the parent plant. There is a greater chance of spreading pathogenic organisms compared to seed propagation. These could include viruses, rust and mildew.

2. Root System Weakness

On occasion, the adventitious root system produced from cuttings fails when rapid growth occurs following planting.

3. Plant Limitations

Not all plants may be propagated successfully via vegetative techniques. Some groups of plants do not possess appropriate anatomical tissue. For example, most monocotyledonous plants are not raised from cuttings (although asparagus


can be propagated this way). Some commercially grown plants are very difficult to propagate vegetatively and, because these techniques produce so few viable plants, they are usually seedgrown. For example, Chionanthus virginicus (North American Fringe Tree) is usually propagated by seed – vegetative reproduction produces only small number of rooted cuttings even under the best of conditions.

4. Need to Maintain Stock Plants

When vegetative techniques are used, the propagator must have access to stock plants (the source of root cuttings, stem cuttings, or leaf cuttings) or be able to purchase these propagules. For hardy perennials (both herbaceous and woody), this may mean a separate area either under cover or in the field for the maintenance of plants in a condition suitable for harvesting propagules. For tender plants, the commercial grower must maintain stock plants under glass. For example, for Fuchsia spp. plants may need to be maintained in a heated greenhouse in order that cuttings may be taken from them in the early spring.

? List some disadvantages of vegetative propagation methods.


Micropropagation

The laboratory technique of micropropagation involves the taking of very small pieces of tissue and culturing these in sterilised media.

Very clean healthy stock can be produced using this technique and large numbers of plants may be produced from an individual in a very short period of time.

When this material is taken from a vegetative portion of a plant (for example, a small amount of callus tissue), the plant produced is a clone of the original plant (that is, it has exactly the same genetic makeup as the parent plant).

Micropropagation techniques are also used to help germinate some of the most notoriously difficulttogerminate seed. For example, seeds of orchids and some carnivorous plants (for example pitcher plants, Sarracenia spp.) are raised in a sterile environment. Agar (a polysaccharide gel) supplemented with hormones and fertilisers provides a suitable environment for a much improved rate of germination. Micropropagation permits the precise manipulation of the environment so seeds can be given exactly what nutrients and hormones have been established as necessary. It limits what the seed is exposed to and also what the seed is not exposed to.


Figure 6 Orchid Seedlings Germinated Using Micropropagation Techniques ∗

Figure 7 Orchid Seedlings Ready for Potting Up

Micropropagation techniques are usually not for most home gardeners.

Genetically Modified Crops

Genetically modified crops can be produced. This is achieved by artificially and unnaturally allowing gene implanting. The result is a genome (or total chromosomal content) which could never have occurred in nature. Plants which have been genetically modified have been propagated thereafter by conventional means using seeds.

∗ These photographs of orchid micropropagation were taken at the Eric Young Orchid Foundation in Jersey.


Seed Versus Vegetative Propagation

Characteristics of Seed Propagated Plants

Characteristics of Vegetatively Propagated Plants

Plants are usually genetically different from the parent plants.

The result is that some of the desirable qualities of the parents may not be reflected in the offspring.

In addition, some of the lessdesirable qualities of the parents may also not be present in the offspring.

Plants are usually genetically identical to the parent plant.

All qualities of the parent plant are shared by the offspring.

Plants produced by seed go through all of the plant growth stages (juvenile, transitional, adult) at the normal rate.

The result may be a plant with a longer than desired juvenile (nonflowering) phase.

Plants produced by vegetative means may have shortened juvenile phases. This means that the desirable adult phase (i.e. flowering and fruiting) may be reached much sooner.

As noted previously, there are advantages and disadvantages of each of the different propagation techniques.

Many plants may be propagated by a number of different methods.

Usually only one method is preferred by commercial propagators – this may be because of the availability of material or the effort required to produce a plant using the technique (that is, the convenience of the technique) or the reliability of the technique.

The home gardener, however, may choose to use a method that is not commonly used in commercial propagation because the factors of mass production and costs are usually not as critical a factor for the gardener wishing to produce only a few plants.

Example: Drumstick Primrose

The white flowered form of the drumstick primrose, Primula denticulata var. alba, may be propagated by a number of methods:

• Seed • Root cuttings • Division of offsets

Usually seed is the method preferred by commercial propagators of the drumstick primrose. A large number of plants may be easily grown without any special equipment.

However, if one suspects that pollination has occurred with the more common lilac


flowering form of P. denticulata, then a vegetative propagation technique should be used. If the seeds were sown, the majority of seedlings would ultimately have lilac flowers and not the desired white flowers.

In commercial propagation, the seeds of a truebreeding white form would not have been permitted to crosspollinate with the white flowered form if the seeds were to be used in propagation. As a result, the seeds would be safe to use to propagate the Primula denticulata var. alba form.

However, in the home garden, isolation of plants to prevent crosspollination is difficult. If the propagated plants must be true to type, then a vegetative process is the suitable choice.

Example: Chinese Wisteria

All seedgrown wisteria have prolonged juvenile periods. In the case of Chinese Wisteria (Wisteria sinensis), a plant grown from seed may not produce flowers until the plant is 20 years old (although this is an extreme, a period of 7 years is not uncommon).

Because the plants are variable, a seedgrown plant may also produce an unattractive flower. It is a long time to wait for a seed to produce a flowering plant only to discover that it does not possess the qualities desired. For this reason, commercial propagation of wisteria use vegetative techniques exclusively.

Wisteria may be propagated by stem cuttings, layering, and grafting (using seed grown root stock).

Production methods focus on stem cuttings and grafting – because these techniques are able to produce larger numbers of plants using a few stock plants and the qualities of the new plants will match that of the parent.

The home gardener, who is interested in only producing a few plants, may consider using layering techniques. Layering will result in plants with the same desirable qualities of the parent without the difficulties associated with rooting stem cuttings or producing successful grafts. This process may be slow (taking more than a year) and may occupy more than a little space in the garden, but it is an effective means of vegetative reproduction.

Figure 8 Wisteria sinensis Cultivar


Example: Rhubarb

Rhubarb (Rheum x hybridum) is another plant where there are a number of propagation alternatives, each with advantages and disadvantages.

In general, rhubarb may be propagated by: • Division • Seed.

Rhubarb seed is fairly easily purchased. It is an inexpensive alternative – a packet of 60 seeds is priced at less than £2. However, the plants produced from these seeds will be variable – some may have desirable qualities while some may have less desirable characteristics. Rhubarb plants are usually selected for diseaseresistance (particularly to root rot diseases), flavour, colour, and length of the stalks. Seed grown plants will not always possess these qualities.

Rhubarb plants are usually propagated by division. The crown is divided into pieces (each with at least one good bud) in early spring or late winter. Each crown is capable of producing a new plant with all the same qualities of the parent plant. However there is a difference in price – a single crown of a known cultivar may cost £3.

In general, commercial propagation of rhubarb focuses on division of named cultivars, although there is some seedbased production. The goal is to produce plants with all the desirable qualities the home gardener demands.

A home gardener, however, would almost always choose to propagate by division. In the case of rhubarb, flowers are not desirable and the home gardener often removes any flowers as they start to form (well before they set seed). Seed saving is therefore not possible. Division, however, is a simple operation that is easily done when the plant is dormant (late autumn may be the best time, although the late winter or spring before new growth commences is another possibility). Divisions are easily grown on to produce plants of harvestable size without any special handling, outside of ensuring the new plant receives sufficient moisture during the first growing season.

In this case, the simplest method for propagation is the one with the most desirable outcome.

Example: Petunia

Although treated as halfhardy annuals in most temperate areas, petunias (Petunia spp.) are in fact tender perennials native to Brazil and Argentina. Their spreading form with generous flowering habit has made them popular plants for both bedding displays as well as hanging baskets.

Petunia may be propagated in one of two ways:

• Many cultivars of petunia are grown from seed. The very fine seed of the petunia is sown in late winter (February) to early spring (April) and grown on, under glass, until temperatures are suitable for planting out.


Many petunia cultivars sold are F1 hybrids. Careful breeding has produced parent strains of plants that, when crossed, produce seeds – producing uniform plants with hybrid vigour, consistent flower colour and regular plant size.

Figure 9 SeedPropagated Petunia

• Some petunias do not come true from seed. These hybrids and cultivars must be propagated vegetatively.

Examples of these include the Surfinia petunias.

Surfinias are valued for their vigour, floriferous habit and tolerance of extremes in weather (from heavy rainfall to drought). Surfinia petunias are hybrids, the result of a cross between Petunia hybrida with P. pendula (a wild South American species petunia). The first plants were propagated from seed (this is how the cross was first made by the breeders) but these plants cannot be propagated from the seed they produce. Some of the superior qualities of Surfinias will not be carried forward to the seedproduced offspring. These are propagated by cuttings.

Surfinias are plants protected by plant breeder’s rights and cannot be propagated without approval by the appropriate agent representing the breeder.

For the gardener, there two options available for the propagation of plants. One is to purchase (or save) seed – germinating and growing the seedlings on to plants in time for the summer display. The second is to produce new plants vegetatively. A gardener may dig up a petunia plant before the frosts of autumn, pot it up and overwinter it in a frostfree place. This plant may be a source of cutting material to be grown into new plants the following spring. However, there are some concerns with this approach – one is that some plants are protected by breeder’s rights and propagating these plants (even for one’s own use) may be illegal, and the second is that these plants must be maintained over winter (and the costs associated with this – space in a heated greenhouse or other location and the risk of overwintering pests and diseases with the plant).

Example: Annual Sunflower

A final example of the choice of vegetative techniques involves the annual sunflower (Helianthus annuus). The annual sunflower is a hardy annual.

This plant is easily propagated by seed. Technically, these plants may be propagated vegetatively by the use of cuttings. However, both commercially and in the home


garden, the propagation method chosen is the sowing of seed. The annual sunflower seed is easily handled, germinated and grown. The only choice left to the gardener is to choose where to sow the seeds – they may be started in late winter under glass or may be sown in situ in the garden in spring.

There is a huge choice of cultivars of Helianthus annuus – ranging in both height (from less than 30cm to more than 3 metres), colour (from the more common yellows through white and red and combinations of shades) and flower form (many are singles, some are doubles, some produce seeds while other flowers are sterile) and plant form (some produce single stems, others are freely branching). Some of these cultivars are F1 hybrids, so saved seed will almost certainly not produce offspring with the desired qualities of the parent.

Figure 10 Fruits/Seeds of Annual Sunflower

? Answers to Self Check Questions from page 11

Can you note down what plant needs might be?

Temperature, moisture, relative humidity, oxygen and for leafy plants in daylight – carbon dioxide, light, its wavelength, intensity and duration, nutrition, hormonal states, as well as enough freedom from competitors and poisons.

? Answers to Self Check Questions from page 19

List some disadvantages of vegetative propagation methods.

Disadvantages of vegetative propagation methods include: 1. The carryover of pests and diseases present on the host plant. 2. Specialist facilities are often required. 3. Cost. 4. There is less chance of new forms arising. 5. While some plant material can be stored for short periods, leafy cuttings

in general are more difficult to store and transport than seeds.

These sunflower “seeds” are actually the fruit of the sunflower – the achene. Within the achene lies the true seed and this is easily removed from the hardened case of the fruit. The entire achene is usually sown to produce new sunflowers.


2 SEED PROPAGATION

By the end of this section, you will be able to describe the conditions for successful propagation by seed:

• Define the terms physical and physiological dormancy. • Describe one method of overcoming a named physical

and a named physiological dormancy. • State the conditions for successful germination of viable

seed. • Describe the seed harvesting and collection of a range

of different plants. • Describe the effects of storage on seed. • Describe how conditions for successful germination can

be achieved in a protected environment. • Describe the sowing and aftercare of a range of seed

types sown in containers. • Describe how the conditions for successful germination

can be achieved in the open. • Describe the sowing and aftercare of a range of seed

types sown outdoors.

Introduction

Propagation by seed involves the following steps:

1. preparing seed 2. sowing of seed 3. germination of seed

Subsequent steps may be required, depending on the location of the seed sowing. These may include some or all of:

• growing on of seedling, • pricking out, transplanting, • thinning, • hardening off.

The actual process of seed germination has been covered in lesson 2. In this lesson more practical aspects of seed propagation are covered.

Seed Dormancy

Dormant seeds are those that, although viable and subjected to favourable environmental conditions for germination, will not germinate.

A seed that is viable that will not germinate because the conditions are not suitable for germination is called quiescent.


Dormancy is an essential mechanism in some plants to time germination when the environmental conditions are favourable for further growth.

Seed dormancy has been a concern of plant propagators for a very long time. As a result, there have been numerous studies of dormancy and a number of attempts to classify dormancy.

Seeds can show varying degrees of dormancy that are sometimes referred to as shallow, intermediate and deep dormancy.

Shallow dormancy is very common and disappears after a few days or weeks. Often seeds are light and temperature sensitive and respond well to mechanical abrasions this is common with herbaceous plants.

Intermediate dormancy is common in conifers and other woody plants where short periods of moist chilling stimulate germination.

Deep dormancy is seen in many plants (woody and herbaceous) in the U.K., a temperate zone. These seeds respond well to prolonged, moist chilling. However, there are some species that require a warm period before a cold moist period, which stimulates radicle and hypocotyl growth, e.g. Lilium, Paeonia spp.

Figure 11 Paeonia Flowers

The type of dormancy condition affecting plants is species dependent. It may be uncomplicated when only one factor has to be removed (single dormancy), or more complicated with two or more factors involved (double dormancy and multiple dormancy respectively). In double or multiple dormancy a sequence of treatments are required and this entire process can take over two years to complete.

Unfavourable germination conditions often throw seeds into dormancy. For example strong light and high carbon dioxide are two factors which often inhibit germination. In some seeds, a lack of light prevents germination whilst others germinate equally well in light or darkness.

It is difficult to generalise but there are three types of dormancy that exist: 1. innate dormancy 2. induced dormancy 3. enforced dormancy.

These terms were introduced in the late 1950s to try to categorise dormancy behaviours.


Innate Dormancy

Seeds that are dormant when shed from the parent plant are said to be in a state of innate dormancy. These seeds are “born dormant”. This may be considered as a physiological condition ∗ when a period of afterripening is required before seeds will germinate. In examples such as the ash tree, Fraxinus excelsior, Acer (including the Sycamore) and Sorbus (including the mountain ash) the embryos are not completely differentiated. This is overcome with time and suitable conditions.

Induced Dormancy

An induced dormancy is one in which the seed has achieved dormancy. Seeds (which may have overcome innate dormancy) can enter an induced dormancy when they are exposed to some unfavourable environmental condition.

Examples of unfavourable conditions include low oxygen levels in the sowing medium (perhaps as the result of deep burial). Induced dormancy may also result from conditions brought about by extraction or storage.

Induced dormancy is characterised by the fact that the state of dormancy remains for a time even after the detrimental factor has gone. The normal physiological processes must then be satisfied before germination can occur.

Lettuce seed (Lactuca spp.) may exhibit induced dormancy. Some lettuce cultivars will normally germinate in either light or dark conditions if maintained at 20°C. However, if the seeds are sown in dark, warm conditions (at around 30°C) and the temperature is lowered to 20°C, these seeds will only germinate if they are given light. The pretreatment of warm, dark conditions provided to the imbibed seed induces a requirement for light.

Enforced Dormancy

Enforced dormancy occurs when a seed (that is capable of germinating) is prevented from germinating by an unsuitable environment. This may involve insufficient water or inappropriate temperatures. When optimum conditions return, immediate germination occurs.

These seeds are not truly ‘dormant’ because they will germinate when conditions are right (a truly dormant seed will not germinate even when the immediate conditions are suitable). Sometimes these seeds are called “quiescent” – meaning that they will not germinate because of an unsuitable environment but will once a suitable environment is provided. Seeds in a packet are quiescent.

Any seed that is placed in an unfavourable condition when it is not dormant will exhibit this type of “dormancy”.

∗ Physiology is the science which deals with the functions of life processes of plants and animals.


Dormancy Mechanisms

The RHS Level 2 syllabus identifies only physical and physiological dormancy explicitly. Other dormancy mechanisms will be briefly identified in this section and are included for completeness only.

Although there is no formally recognised naming convention for dormancy, the work of M.G. Nikolaeva (commencing in the 1960s) and, more recently, two seed researchers (Carol and Jerry Baskin) have resulted in a classification scheme. This scheme identifies two broad classes: • endogenous (due to properties of the embryo – “endo” meaning “within”) and • exogenous (due to properties of the endosperm or other tissue of the seed or fruit

– “exo” meaning “outside”).

Exogenous Dormancy

Exogenous dormancy mechanisms are further broken down into: • physical dormancy (the seed or fruit coat is impermeable to water), • chemical dormancy (germination inhibitors occur within the seed coat or fruit), • mechanical dormancy (the seed coat is a physical barrier stopping development

of the embryo).

Physical Dormancy

Physical dormancy has already been covered in some detail in lesson 2.

The cause of physical dormancy is the seed coat (or testa). These hardened seed coats have become impervious to water because the tissue has become suberised (the cells have been impregnated with a substance called suberin). The advantage of these types of seed is that they tend to have a long storage life, once dried to a suitable level – even seeds stored at warm temperatures remain viable for long periods.

Studies of dormancy determine the source of the block to germination by a series of experiments – one of which is the removal of the embryo from the seed and the attempt to grow this isolated embryo using laboratory techniques. If the removed embryo grows successfully, then the embryo is not dormant, it is merely waiting for clues of a suitable growing environment but these clues are blocked by the seed coat barrier.

This type of dormancy may be overcome either through:

• a treatment of the seed coat called scarification

Scarification involves the injury to the seed coat to permit the entry of moisture into the seed’s tissues. These treatments will be outlined later in this lesson. The seeds of sweet pea (Lathyrus odoratus) sometimes need scarification before sowing to ensure germination. Other seeds with this type of dormancy include


Lupinus, Geranium (Cranesbill), and Convolvulus (Bindweed).

Figure 12 Cranesbill (Geranium sp.)

• the sowing of slightly immature seeds (where the seed coats have not yet had a opportunity to harden). This procedure takes advantage of the fact that hard seed coats usually develop during the final stages of seed development. Early sowing of the seeds of Baptisia australis (Wild Indigo) is an example of a seed with a physical dormancy that may be germinated without any other special treatment.

Chemical Dormancy

When the seed coat contains chemical inhibitors, the seed exhibits a chemical dormancy. This occurs in many tropical plants where the pericarp is fleshy. Leaching or absorption of the soil reduces the amount of the chemical, permitting the seed, ultimately, to germinate.

A second type of chemical dormancy occurs when the seed embryo contains inhibitors, but the seed coat prevents these from leaching away. Germination will not occur until these inhibitory chemicals are permitted to leach away.

Plants with fleshy fruits often present this type of dormancy. The seeds of the tomato (Solanum esculentum) exhibit chemical dormancy – when the tissues of the tomato are removed, the chemical inhibitor is removed.

Mechanical Dormancy

In mechanical dormancy, the seed coat acts as a physical restraint on the embryo. Examples of seeds exhibiting this type of dormancy include the hard shells of the walnut (Juglans spp.) and the hardened pericarp of Hawthorn (Crataegus spp.).

Endogenous Dormancy

Endogenous dormancy involves some quality of the internal tissues of the seed that prevent germination. This category is divided into three groups: • physiological dormancy involves a mechanism in the embryo that prevents

germination from commencing, • morphological dormancy involves the incomplete embryo development that

prevents germination, • morphophysiological dormancy (which involves a combination of the first two

categories).


Physiological Dormancy

Physiological dormancy has also already been described in lesson 2.

Seeds with physiological dormancy have some aspect of the embryo itself that prevents germination. The embryo is fully developed, but must complete some kind change before germination may occur. Physiological dormancy has been further broken down into three groups based on the intensity of the dormancy: nondeep, intermediate, deep.

In some instances, seeds with nondeep physiological dormancy may need such a short treatment that they may germinate immediately upon sowing. The short period of dry storage that occurs between harvesting, postharvest preparation, packaging and shipping may be sufficient to overcome any dormancy that may have occurred. During this time, “afterripening” may have occurred. Afterripening is the maturation of the embryo during dry storage that enables it to germinate when sown. The seeds of many flowers sold in packets, most vegetables and grasses exhibit this type of dormancy. For example, the seeds of cucumber (Cucumis spp.) have non deep physiological dormancy as well as such commonly grown garden annuals as Calendula (Pot Marigold) and Helianthus (Sunflower). If these seeds are sown immediately upon harvesting, they may not germinate. One theory is that the seed needs a signal to indicate it has left the parent plant before germination may commence.

In others with nondeep physiological dormancy, a period of light or darkness is necessary to germinate – these seeds are called photodormant. The seeds that exhibit this type of dormancy are most likely sensitive to levels of phytochrome. Lesson 2 describes the mechanism involved with detection of phytochrome in the two forms Pr and Pfr. Many common bedding plants also exhibit photodormancy – for example the tiny seeds of Begonia spp. and the seeds of Busy Lizzy (Impatiens walleriana) need light to germinate. Seeds of Nigella are the opposite and need darkness for germination.

Seeds with intermediate or deep physiological dormancy need a period of storage in a moist state. Sometimes seeds with these types of physiological dormancy are treated with a period of chilling (called stratification). Later in this lesson, stratification is described more fully. Seeds that exhibit this type of dormancy are often classified as obligate (meaning that they require special treatment) or facultative (meaning germination without stratification will occur, but the chilling process increases the rate of germination). The seeds of many temperate woody plants exhibit this type of dormancy – for example, the seeds of most Acer species require moist chilling before germination will occur. There are some annuals and perennials that fall into this classification of dormancy. Penstemon, Primula and Aster require periods of chilling before germination will commence while Antirrhinum and Salvia do not require chilling but will germinate faster following a chilling treatment.

Morphological Dormancy

Morphological dormancy involves those seeds where the embryo is not completely formed or developed at the time the seed completes ripening. Usually, these seeds require warm temperatures to permit the embryo to complete development. This may reflect an adaptation to the climate where the seed dispersal occurs in late


summer and, even if the autumn remains warm, germination will be delayed until the following spring. This type of dormancy may also prevent overcrowding of germinated seedlings. Some examples of the many plants with seeds with morphological dormancy include Anemone, Cyclamen, and Hosta.

Temperature conditioning and hormonal treatment can break this dormancy artificially – the precise requirements varying from species to species. Germination will not occur until the embryo has reached a fully developed stage.

Morphophysiological Dormancy

This form of germination dormancy involves both an underdeveloped embryo (of Morphological dormancy) and a physiological mechanism (of Physiological dormancy). To break this dormancy, two sets of conditions are needed – to complete development of the embryo and then to break its dormancy. The seeds with morphophysiological dormancy are said to have a double or multiple dormancy.

The common ash (Fraxinus excelsior) exhibits this type of dormancy – this seed has an immature embryo. After embryo maturation (provided by warm temperature) there is a requirement for a cold temperature treatment (provided by temperatures less than 5 o C). In practical terms, this requires the seeds to be placed in a stratification pit for the first winter and summer after collection. This is followed by a second winter in the stratification pit before germination will occur. Or the seed may be placed in a cold store for the “winter” treatment and then a warm store for the “summer” treatment. Some seeds require the opposite treatment – first a period of cold, then a period of warm.

Double and Multiple Dormancy

Not all seeds with double dormancy exhibit morphophysiological dormancy. Some have a dormancy of the seed coat and a physiological or morphological dormancy. Any combination of two or more different forms of the exogenous and/or endogenous dormancy are called double (or multiple) dormant.

The seed of the Dove Tree or Handkerchief Tree (Davidia involucrata) is doubly dormant. This seed has both a physical dormancy involving the seed coat and a physiological dormancy involving the embryo. This seed requires storage in a warm, moist medium until the radicle emerges and then storage in a cold, moist medium for about 3 months. Unlike some seeds with a dormancy related to the seed coat, the recommendation for this one is that the fruit (a drupe) be planted without removal of the coating around the seeds.

Figure 13 Davidia involucrata Ready for Warm Storage

The seeds of the Dove Tree (Davidia involucrata) do not need to be removed from the drupe fruit before planting. They should be placed in moist vermiculite and then placed in a warm location (usually about 20°C) until the radicle emerges. A polythene bag with moistened vermiculite will be used. After the radicle emerges, the moistened vermiculite and seeds will be stored at about 5°C for 3 more months. Then the seeds may be sown outdoors.


Seeds in nature tend to germinate the following spring or over a longer period.

TREATMENTS FOR DOUBLE DORMANCY Paeonia suffruticosa (tree peony) Two periods of storage required to address the

morphophysiological dormancy: • first a warm period to allow radicle growth, • then a cool period to allow epicotyl development

The breaking of the epicotyl dormancy is influenced by the stage of growth of the radicle. The greater the radicle growth, the faster and more effective the chilling treatment is for the growth of the epicotyl.

Cercis canadensis (North American Redbud) Two treatments required:

• mechanical scarification or immersion in either boiling water or sulphuric acid to address the physical (seed coat) dormancy,

• then moist chilling (stratification) at about 2 to 5°C for 5 to 8 weeks to address the physiological (embryo) dormancy.

(The treatment with sulphuric acid may only be applicable in commercial horticulture due to the hazard of the acid.)

Viburnum spp. Two periods to address morphophysiological dormancy: • first a period (2 to 6 months) of high temperatures to

stimulate radicle • then 1 to 4 months of low temperature to encourage

epicotyl development

Other examples include Convallaria, Sanguinaria, Trillium and Polygonatum

Treatments to Overcome Dormancy

Scarification

Scarification is the process whereby the seed coat is deliberately damaged prior to sowing the seed. This seed coat, when damaged or etched, has tiny openings through which moisture and gases can cross. As a result, the first stage of germination may commence. The goal of scarification is to address the physical dormancy associated with an impermeable seed coat.

Seed coats are damaged by: • scratching, • cutting (also called chipping) or puncturing, • soaking in water or acid, • alternately freezing and thawing, or • fire (this melts the resins in or around the seed coat).


In nature, seeds with hard seed coats are softened by the actions of chemicals and microorganisms within the soil. In addition, the abrasive nature of some soil particles may also play a role. And natural cycles of freezing and thawing often weaken the seed coat. The acid of digestive systems of animals and birds also can help break down the impervious quality of hard seed coats.

There are a number of methods to scarify seeds:

• Scratching the seeds with sandpaper to remove or thin a portion of the seed coat.

One technique that is useful especially for small seeds (that are difficult to chip with a knife without causing extensive damage to the seed) involves sandpaper and a jar. The sandpaper is placed in the jar so that the abrasive side faces the centre of the jar. The dry seeds are placed into the jar. The cap is replaced and the jar is shaken so that the seeds make contact with the sandpaper. The goal is not to remove the seed coat, but to etch it slightly.

Figure 14 Scarification of Seeds

Commercially, this technique is accomplished by rotating the seed in drums lined with sandpaper or mixed with gravel. Dry tumbling can also aid germination in plants such as Acacia.

• Chipping the seeds with a knife to remove a small portion of the seed coat or puncturing the seeds to provide an opening in the seed coat.

Please refer to lesson 2 for an illustration of chipping with sweet pea seeds. Care must be taken, particularly when handling small seeds, to avoid cutting fingers in place of seed coats.

• Soaking the seeds in water for a short time.

For resolution of physical dormancy, the seeds are dropped into a volume of boiling water – the source of heat is immediately removed (the intention is not to cook the seeds) and the water is permitted to return to room temperature. About 12 to 24 hours later, the seeds are removed. This will help soften the hard seed coat. Examples of these seeds include Beetroot (Beta vulgaris).

For resolution of chemical dormancy, the seeds may be soaked in water between 5 10 o C for 24 to 48 hours. Plants such as Pinus and Ceanothus


seeds may be treated in this way. Soaking the seed can also increase the speed of germination and emergence especially with those seeds, which are slow to germinate.

• Soaking the seeds in concentrated sulphuric acid. An acid bath is sometimes used by the commercial grower (under carefully controlled conditions to prevent injury to workers). Seed should be mixed as 1 part seed to 2 parts acid at 18 21 o C for 1 to 2 hours. The seed coat becomes carbonised and the seed expands. It is of obvious importance that the embryo should not be damaged during this process so close observation is required. Following this treatment, the seeds are washed thoroughly and sown immediately or dried and stored. Examples are rose rootstocks, Hamamelis, Daphne and Tilia.

It is important that scarification be done carefully to ensure that the seed contents (in particular, any parts of the embryo) are not damaged.

Seeds can be stored for periods of time after mechanical scarification. Examples include Wisteria, Cercis, Cytisus, some pines and Cornus. These seeds must be stored carefully, however, because they are more susceptible to invasion and damage by microorganisms that are now free to enter through the damage in the seed coat.

Stratification

Stratification is the process whereby the seeds are subjected to a period of chilling (and sometimes warming) after the seeds have been imbibed. The goal of this procedure is to address seed dormancy. Usually only seeds of plants of the temperate zones with cold winters require this process. The process of stratification is sometimes called “moist chilling”. Low temperatures (usually below 5°C) are involved in this process.

Many woody tree and shrub seeds require this treatment. Examples include Sorbus, Crataegus, Acer, Fraxinus, Berberis, Cotoneaster, Rosa they all have complex dormancy characteristics.

The exposure to low temperatures allows physiological changes to take place within the embryo, as may occur with after ripening. Although some species may not require stratification, their germination may be quicker and more uniform after being subjected to stratification. For the commercial grower, a uniform germination rate is particularly useful because it allows for a production of a uniform product.

The procedure is simple. Seed is mixed with moist sand, peat, vermiculite, or a combination of these ingredients. The ratio used is approximately 3 parts of sand/peat/vermiculite to each part of seed. The seed mixture is held at warm, room temperatures for about 12 to 24 hours to permit the seed to imbibe moisture. Then the mixture is placed in cold conditions.

Seeds in stratification units should be checked each month. Seeds must be put in and taken out at the correct time. Seeds should be sown immediately following removal from stratification units. It is important to examine the containers fairly frequently (particularly after about 2 to 3 months of treatment) because once the seed begins to germinate, it should be sown at once.


Originally, this procedure involved the digging of pits outside. Perfect drainage was ensured in the pit (by adding a layer of coarse stone or sand). The sides of the pit were lined with timber (and a fine wire mesh – perhaps 6mm – to prevent the entry of rodents and to establish the exterior perimeter of the pit. Then layers of a seed/sand mixture were added into the pit. The use of layers is where the term “stratification” comes from. The entire mixture was covered including another wire mesh layer to prevent rodents from entering. The contents of the pit were then subject to natural outdoor temperatures (cold in winter, warm in summer). All of this needed to be protected from damage by animals – particularly mice.

Sometimes this is done using pots. The bottom of the pot has stones for drainage. Above this were layers of sand and seed. The entire pot was protected with mesh (to prevent animals from eating the seed). The pot was placed outside in a relatively protected area – sunk up to the surface level in a pit prepared in a suitable location outside (this pit needed perfect drainage to prevent the seeds from rotting). Again, the contents of the pot were subjected to the natural changes in temperature and were kept moist by precipitation. This technique is still sometimes used today.

Figure 15 Seed Stratification

However, much stratification today is carried out using containers (often polythene bags) to hold the moist seed/sand/peat/vermiculite mixtures. For cold stratification, these are placed in either the refrigerator or cold storage. For warm stratification, these may be kept indoors, in a heated location, or outdoors when temperatures are suitable and the container is kept out of sunlight.

The home gardener may stratify some seeds using the same procedures. Often re sealable polythene bags are the best because they can lie flat, are easily written upon (to record the contents and the date they entered storage), and can be quickly checked to follow the progress of the seed. Some seeds will actually germinate in the cold storage conditions, so the transparent nature of the plastic bags makes this easy to check.

Some people advocate the use of folded, moistened paper towels. This method is outlined in some detail in “Seed Germination: Theory and Practice” by Norman C. Deno. This procedure is particularly useful for home gardeners because seeds undergoing stratification (both cold and warm) may present little mess (since no sand, vermiculite or peat is used) and take up little space in a refrigerator or cabinet. The concept is to use moistened paper towels to act as the source of moisture for the seeds. The seeds are placed on these paper towels. The towels are folded, labelled and stored in polythene bags. Periodically, these packages may be removed from storage and checked for signs of germination. Germinated seeds may be removed

view through the centre of the pot

mesh

stones for drainage

alternating layers of sand and seeds


and planted up for growing in the light. A large number of seeds may be stratified this way and still fit within a single polythene bag.

Figure 16 Seed Stratification for the Home Gardener

The important points are that the seeds must not be kept wet, just moist. When the seed mixture is enclosed in a container or polythene bag and held indoors in a cool location (a refrigerator or cold storage), excess moisture is not an issue. However, seeds being held outside need to be stored in such a way that they will not remain wet.

Seeds also need to respire (although at a reduced rate when temperatures are low) so the containers must permit some exchange of oxygen and carbon dioxide with the outside air. Polythene bags do permit some exchange of air and are suitable for the home gardener to use.

Examples of Seed Treatment to Overcome Dormancy

The following table is a list of some tree species and the conditions for storage of the seed. However, this list is not to be memorised for the RHS Level 2 Certificate in Horticulture examination. The information in this list is being provided to illustrate the scope of seed storage periods only. There are many web sites on the internet that provide germination and storage information. In addition, there are a number of references that list similar information. See the reading list at the end of this lesson for a starting point.

In the table below, a number of woody perennial species are listed along with the treatments to overcome dormancy. The dormancy conditions identified include:

• embryo dormancy (a physiological dormancy) • seed coat dormancy (a physical dormancy).

The first step is to remove the seeds from seed pods or fruits. Then place these seeds onto a moistened paper towel that has been folded in half. This paper towel should already be labelled (using a waterproof marker) with the seed species and date of start of storage.

The second step is to fold the paper towel again (so the seeds are between moistened layers) and place this inside a polythene bag. If more seeds (from different species) are being started with the same treatment, then these may also be added (using different paper towels) into the same bag.


SPECIES DORMANCY TREATMENT Acer macrophyllum Embryo Stratify 2 months at 5 o C. Acer platanoides Embryo Stratify 3 4 months at 5 o C. Acer saccharum Embryo Stratify 2 3 months at 2 5 o C. Alnus incana Embryo Stratify 2 months at 5 o C. Arctostaphylos uvaursi Seed coat and embryo Acid soak for 3 6 hours then stratify at

25 o C. for 2 months and further stratification at 4.5 o C for 2 months.

Berberis spp. Embryo Stratify for 15 40 days at 0 5 o C. Ceanothus thyrsiflorus Embryo and seed coat Hot water treatment for 12 hours at 71 o C.

followed by stratification for 3 months at 2.5 o C.

Ceanothus arboreus Seed coat Hot water treatment for 12 hours at 76 100 o C.

Chamaecyparis spp. Embryo Stratify for up to 3 months at 4.5 o C Clematis spp. Embryo Stratify for up to 3 months at 4.5 o C Cornus nuttallii Seed coat and dormancy Stratify for 4 6 months at 0.5 5 o C. Cornus stolonifera Embryo and seed coat Scarify followed by stratification at 5 o C. Cotoneaster horizontalis Embryo and seed coat Acid soaking for 1.5 hours followed by

stratification for 3 months at 5 o C. Cupressus spp. Embryo Stratify for 2 months at 5 o C. Fagus sylvatica Embryo Stratify for 3 months at 5 o C Fraxinus excelsior Embryo and seed coat Stratify for 2 3 months at 20 o C to break

seed coat dormancy then at 5 o C for further 2 3 months to break embryo dormancy.

Hippophae rhamnoides Embryo Stratify for 3 months at 5 o C Ilex spp. Immature embryo Stratify for up to 3 years at 5 o C. Larix spp. Embryo Stratify for 1 month at 5 o C. Magnolia spp. Embryo Stratify for 6 month at 5 o C. Malus baccata Embryo Stratify for 1 month at 5 o C. Malus pumila Embryo Stratify for 2 3 months at 5 o C. Picea spp. Embryo Stratify for 2 3 months at 5 o C. Pinus spp. Embryo Stratify for 2 3 months at 5 o C. Platanus spp. Embryo Stratify for 1 3 months at 5 o C. Prunus avium Embryo Stratify for 3 4 months at 1 5 o C. Prunus padus Embryo and seed coat Stratify for 1 2 months at minus 1 5 o C Quercus spp. Some embryo dormancy

may be present Stratify for 1 2 months at 1 5 o C.

Rhus spp. Seed coat Acid soak for 1 1.5 hours followed by stratification for 1 2 months at 5 o C.

Robinia pseudoacacia Seed coat Acid soak for 1 1.5 hours and sow immediately

Sorbus aucuparia Embryo Stratify for 3 months at 0 1 o C. Symphoricarpos spp. Seed coat and embryo Stratify at 20 26 o C for 4 months followed

by 4 months at 5 o C. Taxus spp. Seed coat and dormancy Acid soak for 1 2 hours followed by

stratification for 3 4 months at 0 5 o C.


SPECIES DORMANCY TREATMENT Tilia cordata Seed coat and embryo Stratify for 4 5 months at 15 25 o C

followed by 4 5 months at 1 5 o C. Viburnum acerifolium Embryo Stratify for 6 10 months at 20 30 o C to

produce root growth then 2 4 months at 5 o C to promote shoot growth.

Viburnum opulus Embryo 2 3 months at 20 30 o C followed by 1 2 months at 5 o C.

External Environmental Factors Affecting Germination

A note on viability: To be viable, seeds must normally have been fertilised and contain a living embryo. They should also be collected at the correct stage of maturity. Premature harvesting may arrest development and shorten storage life. Delayed harvesting may lead to rapid deterioration or loss by natural dispersal. Conditions of storage also affect the viability and longevity of seeds. Dry seeds remain viable longest under cold, dry storage conditions of low humidity. Other conditions that contribute to maintaining the viability of seeds are artificial drying of the seed, and a reduction of the oxygen supply. Sometimes large seeds produce a better seedling.

? Which of the following would rapidly kill germinating seed, and why? • excess moisture • excess air/oxygen • excess heat

Check your thoughts at the end of this section.

The four main external factors, which affect germination of the viable seed, are:

• water, • gases, • temperature, • light.

The environment should also be free of diseases (for example, the organisms that lead to the development of dampingoff) and free of competition from other crop plants or weed plants. Later, as the seedling develops, the new plant should also be grown in a compost or soil with adequate nutrition to support the plant growth and maturity.

Water

Water is essential for the germinating seed. In the case of many seeds (not recalcitrant seeds that have been maintained moist since they ripened and were harvested), the first step is to rehydrate the seeds.

Water is the most important factor that affects the germination of seed. Absorption of water is the first stage of germination. This water must be present in the compost


or seedbed and available to the plant.

For seeds being sown in containers, peat is added to seed compost because of its capacity for holding moisture. Pots or boxes are watered immediately after sowing (or, in some cases, immediately before sowing). The pots or trays are then usually covered with glass and paper, or polythene. This prevents evaporation and makes further watering before germination unnecessary.

The waterholding capacity of the outdoor seedbed relies largely upon the residue of bulky organic manures. Again, it is important to see that the soil is well supplied with moisture before sowing, to avoid watering again before germination. In dry soil, the open drills can be watered before sowing (on a small scale). Firming after sowing permits the seed to come into close contact with moisture on and in the soil particles.

One technique for watering compost in containers involves the use of a water bath. The compostfilled container is placed in a very shallow bath of clean water – the idea is to submerge only the bottom of the container and not the entire container. Water will be pulled up by capillary attraction through drainage holes in the base of the container. This method does not reduce the quality of the soil structure and does not dislodge the seeds.

Stand the seeded pans in the water for capillary attraction to absorb the water. When the pan is fully moist, remove the container from the water bath and set it where the seeds are to germinate.

Figure 17 Watering from Below

It is essential that moisture remain available to the seed during the entire process of germination. The lack of available water is the most common cause of seed death or seedling death.

Gases

The germinating seed is respiring. As a result, the rate of germination decreases if oxygen levels are decreased.

Carbon dioxide that is produced by the germinating seed (as a consequence of the respiration process) must be permitted to escape from the growing medium. Elevated levels of carbon dioxide also lead to decreased rates of germination. This is one reason why it is essential to maintain the soil structure during germination – the formation of a cap on the soil surface (from vigorous irrigation, for example) will

seeds

water bath


prevent the exchange of oxygen and carbon dioxide gases between the atmosphere above the soil and the soil atmosphere.

The exception to this is seed that germinates and grows in aquatic environments. For example, North American Wild Rice (Zizania sp.) will germinate in anaerobic environments, when the seed is fully emersed.

Temperature

Temperature requirements vary greatly for different kinds of seed. Temperature influences the rate of metabolic processes (one of which is respiration), and this is an important step in germination. This does not mean, however, that all seeds require warm temperatures to germinate. The optimum temperature range varies from seed to seed. Some seeds will even germinate during cold storage.

Germination may be prevented if the temperature is very high or very low. Seeds of pansy (Viola spp.), which have been sown in June, need to be kept below 12 o C.

In controlled conditions under glass, seeds can be supplied with the ideal germinating temperature. The covering of glass and paper or polythene will help to maintain the temperature in a seed tray. The use of newspaper, in particular, is necessary if containers are situated where hot sunshine falls on them – the temperature inside the glass covering would otherwise become excessive.

Outside, little control is possible. Timing of sowing is critical. Ensuring that soil is well drained will help increase soil temperature early in spring.

Some seeds, particularly seeds of wild plants, require fluctuating temperatures. For these seeds to germinate successfully, a regime of temperatures may need to be followed – often these seeds require different daytime temperatures than nighttime temperatures.

Light

The common belief is that seeds will only germinate in darkness. There are some seeds that require darkness to break dormancy, but most seeds either require light or are tolerant of both dark and light.

Examples of seeds requiring light include: • Lamium purpureum (red dead nettle) • Arabidopsis thaliana • Sinapsis arvensis (charlock) • Primrose • Impatiens, Petunia

Seeds whose germination may be inhibited by light include Tomato.

The mechanism involved in the detection of light involves phytochrome and its two interchangeable forms. Please refer to lesson 2 for details about this mechanism. Buried seeds (or those seeds in the shade of other plants) will receive little red light, and more light in the farred wavelength range. The consequence is that phytochrome is converted into the red form (Pr) – this inhibits the germination of light


sensitive seeds. Many small seeds are light sensitive because they have only a small reserve of energy that cannot support extensive growth to the soil surface to commence photosynthesis. In fact, most small seeds would not be able to grow to reach the surface and this may be why this adaptation has occurred.

Seed Harvesting and Collection

The goal of harvesting or collecting seed is to collect viable seed. Through correct treatment and storage conditions, the viability of the seed will be retained. There is little point in saving a seed that no longer has the ability to germinate.

There are different approaches to collection of seed. But some basics apply to every seed:

• Collect seed when it is mature (or, when necessary, just slightly immature). • Do not save diseased tissue; do not save seeds with insect damage.

A quick note about collecting seed from plants in the garden: Some plants produce viable seed that does not breed true. That is, the seed will not produce a plant with the same qualities as the parent plant. In particular, the seeds of the F1 hybrid may not produce plants with the same qualities as the parent. However, the seeds of many other plants (including most varieties termed “heritage” or “heirloom”) will breed true. These “openpollinated” varieties tend to have stable traits from one generation to the next.

Seeds of Woody Perennials

For tree seeds, once mature, carefully pick or collect the fruit (this may be a dry fruit, for example the pods of Cercis, the Judas Tree, or a fleshy fruit, for example the berries of Sorbus spp.). At this point, identify the source of the seed (it may be difficult to tell the difference between seeds later) – try to determine both the genus and specific epithet of the plant whenever possible.

Seeds within fleshy fruit must be removed from the pulp. For larger fruit (for example, the seeds within an apple, Malus sp.), the seeds may be picked out from within the fruit. For smaller fruit (for example, the berries of Sorbus spp.) the berries must be pulped, mixed with warm water and left for several days. After this time, the seeds should have sunk to the bottom of the water. These seeds should be carefully removed (ensuring that the pulp has been removed successfully) and dried.

Figure 18 Collecting Seed from Cotoneaster spp.

After extracting the hard seeds from the pulp, the seeds are washed clean before sowing or drying and storing.


Winged seeds (for example the samara of Acer spp.) or those seeds within a catkin (for example the small samara of birch, Betula spp.) should be collected before the seeds are dispersed. In the case of catkins, the entire catkin can be placed in a paper bag ∗ and left for several days to two weeks – during this time, the seeds should have separated from the catkin and may be saved. In the case of individual samaras (like those of maple, Acer spp.), the wings of samaras may either be kept intact or rubbed off (to make the handling of seeds easier).

Collecting seeds from cones is as simple as placing the cone in a paper bag in a warm, dry location. The cone will open and the seeds will be released.

Seeds of Herbaceous Perennials, Biennials and Annuals

Collecting and saving seeds from annuals, biennials and herbaceous perennials is one way of propagating new plants. Many perennial, annual and biennial species produce capsules or pods, within which the seeds are found. It is important to collect the seed when it has ripened, but before dispersal has occurred – for example, it is usually best to save seed that has not yet come into contact with the soil. The most ideal conditions for collecting seed is a dry day – wet seeds, unless dried sufficiently before storage, are at greater risk of rotting during storage.

Collect pods and capsules when ripe (often a colour change from green to brown or black is a clue that the seeds are ripe). Then, over a piece of paper, crush them carefully (usually using your fingers is the best way to prevent damaging the seeds). Seeds will be released onto the paper – where they may be left to dry before packaging in glassine or paper envelopes. It is critical to label the seeds at this time. Usually the name of the plant (including variety or cultivar name, if known) and the date of collection are adequate.

Some seedpods eject the seeds with considerable force when ripe. For these plants, it is best to enclose the seedpods within paper bags so that the natural ripening process can occur but the seeds will remain within the bag.

The seeds of the annual LoveinaMist (Nigella damascena) often do come true from seed (meaning that the seeds collected from garden plants will often produce new plants with the same qualities as the parents). These seeds are easily collected and removed from the decorative, inflated seed produced.

Figure 19 Seed Capsule of Nigella damascena The seeds of poppies (whether annual, biennial or perennial) are easily collected from the “pepper pot” shaped seed capsules.

∗ The use of paper bags, and not polythene bags, is critical. Paper will permit the seeds to remain dry. While polythene bags will trap moisture and permit the growth of undesirables like different fungus that may lead to the seeds rotting.

Contents within a split capsule


Figure 20 Seeds of Poppy (Papaver sp.)

Case Study of Primula japonica

Primula japonica is a stunning late spring flowering herbaceous perennial for damp soil in dappled shade. The whorls of flowers are produced on sturdy stems. Six or seven whorls develop over several weeks. Here they are seen in midMay with the first and second whorls just starting. These are one year old plants.

Figure 21 Primula japonica Flowers in May

By late June, the seed pods are forming and by late July they are ready to collect.

Figure 22 Seed Pods of Primula japonica

By late July the seed capsules are full of ripening seeds. The flowers are selffertile


and so different coloured forms routinely but not always come true. Because P. japonica are reasonably reliable at selfpollination there is no need to isolate these plants from other species of Primula. Very special cultivars would normally be kept at a distance from other plants (to ensure crosspollination does not occur).

The seed capsules are removed just before the ripe seeds fall to the ground. Timing is critical as the seed is dispersed quite quickly. The seed trays are placed in a cool dry airy shed until the seeds fall readily from the capsules.

Figure 23 Collected Seed Pods of Primula japonica

Please note that each tray is labelled. Within some of these trays, some loose seeds are visible.

When the seeds have ripened and fallen from the capsules it is time to clean the seed before storage. Once the capsules are dry, they are slightly crushed between thumb and finger before being placed in the sieve. They are sieved to remove all extraneous material such as capsule parts and small insects. An ordinary domestic flour sieve is perfect for Primula seed. However, do not use this sieve for cooking because some seeds may be poisonous and it is not worth the risk of contaminating food with seed residues.

Figure 24 Seed Cleaning

Seeds must be stored in packets, which do not let moisture in. These moisture resistance packets are perfect for small quantities of seeds. Clean paper envelopes


can do, if glassine envelopes are not available, athough paper envelopes may absorb moisture more readily than the glassine ones (this is particularly a concern if they are being stored within a refrigerator). It is important that the envelopes be labelled with the name of the species (and perhaps cultivar or variety) and the date of seed collection.

Figure 25 Glassine Seed Packets

Finally the packets of seeds are stored in a domestic refrigerator (with the permission of the person in charge!)

Figure 26 Refrigerated Seed Storage

These seeds are stored within the refrigerator only to ensure that they remain viable until the time they are sowed. It is important that the containers are airtight – if the containers are not airtight, then there is a risk that moisture may condense on the seeds.

These seeds are not undergoing stratification to overcome dormancy. In this case, the seeds are collected in between midJuly to September and are sown the following February (under glass) – refrigeration is used only to ensure the viability of the seed remains as high as possible between collection and sowing.

Be careful these seeds are not inadvertently eaten or come into contact with food.


Seed Storage

Seed storage has two functions. One is to keep seed from one growing season to another. The other is to permit the seed to overcome any dormancy condition.

In lesson 2, an overview of seed storage techniques was described. The basic approaches are:

• temperature Provide conditions that will slow the seed’s natural respiration rate. Often low temperatures result in seed remaining viable for the longest time. Avoid temperature fluctuations.

• moisture Keep desiccanttolerant seeds dry. Because seeds are hygroscopic, even moist air is sufficient to affect the moisture content of seeds. Wet seeds often rot. For this reason, keep the dried seeds in an airtight container and maintain the dryness of the air within the container through the use of silica gel.

Only store recalcitrant seeds in suitable (moist) conditions. These seeds, in general, do not store for long.

• gases Seeds continue to respire even in storage. For seeds stored dry, there is little respiration (this has been limited by both temperature and moisture levels), so exposure to oxygen has little effect on storage.

Recalcitrant seeds (those stored in a moist condition) will require oxygen in storage.

Storage of seeds may influence: • viability (the number of seeds that will germinate when ideal conditions are

provided), • vitality (the rate that the seeds germinate – that is, the speed of the

germination and the vitality of the seedling that results) • dormancy

Some seeds overcome dormancy during storage. Other seeds will develop dormancy during storage. The seeds of Baptisia australis (Wild Indigo) develop seed coat dormancy when the seed coat dries.

For the home gardener, avoid keeping seeds in the kitchen drawer (the temperature fluctuations will cause premature aging of the seeds), garden shed or greenhouse (the seeds may become damp in these conditions).

Commercial seed companies often seal their seeds in foil packets to keep the moisture away from the seeds and to reduce the amount of oxygen that the seeds are exposed to. When only some of these seeds have been sown, use sticky tape to reseal the remainder in the foil packet in which they were purchased.

Some seeds require a period of storage before they will germinate. Usually these seeds are exhibiting a type dormancy of within the seed, involving the embryo. The embryo may be dormant or may not be completely formed. Warm, dry storage may be the only step required to overcome this dormancy (for example, the seeds of


Calendula) or may be the first step required to overcome this dormancy.

The two main points of seed storage are:

• When saving dry seeds, use glassine envelopes, paper bags or envelopes, or cloth bags. Avoid using polythene bags, because these trap moisture (should the seeds not be completely dry) and the seeds may rot.

• Know what conditions are necessary for the specific species of seed is being collected – some tolerate or require dry storage to remain viable, others are not tolerant of drying (these seeds are often called recalcitrant seeds) and must be collected when moist and stored in moist conditions.

Treatments

Many of the seeds sold in packets have undergone some treatment by the grower. These include priming, pelleting, coating and dusting.

An additional treatment is chitting. Seeds that have been chitted have been pre germinated. Although commercial growers may be able to purchase this type of seed, it is unlikely that a home gardener would have access to seeds with this pre treatment. Usually, these seeds are sold in plastic containers (to protect the emerged radicle). However, the home gardener may pregerminate seeds at home – effectively, producing chitted seeds themselves.

Figure 27 Chitted Seeds

Seed Priming

A primed seed is one that has been pretreated so that it germinates quickly and uniformly. Primed seed is of particular value to the commercial grower, since the irregularity of germination in many seed species (for example Phlox drummondii and Verbena) cause problems in nursery growing programmes. This irregular germination results in increased production costs (both in terms of space and heating). Priming is also common practice with some vegetable seeds – including carrot, leek, celery and parsnip.

The principle of 'seed priming' is based on the fact that seeds must imbibe water prior to germination. If imbibition is controlled throughout a sample of seed, a state of preparedness is possible. All seed should subsequently germinate and develop at

These sweet pea (Lathyrus odoratus) seeds were chitted by first soaking in water overnight and then by storing in a rolledup, moistened paper towel for several hours (in a warm location). Remember, seeds need both oxygen and moisture to germinate. When sowing chitted seeds, some care must be taken to ensure the radicle does not become injured.


the same rate. The actual process used commercially uses the chemical polythylene glycol (PEG). This rehydrates the seed but it does not permit the seed to completely germinate. The seeds become metabolically active and are prepared for germination. PEG acts as an osmoticum and, because of its large molecular structure, allows only sufficient water into the seed to permit limited germination. The radicle is just ready to protrude. Following priming, seeds can be dried and stored for many months in this primed state.

The technique used is:

1. Temperature should be constant and appropriate to the species 2. Dissolve polythylene glycol crystals (creamy white) in distilled water overnight 3. Treatment lasts for about 14 days in an airtight container to prevent

evaporation 4. Bottom of container lined with capillary matting 5. Moisten with polythylene glycol 6. Sprinkle seeds on to surface of matting 7. Test samples for percentage germination. When this reaches 80% priming is

complete. 8. Rinse primed seeds in cold running water and dry at room temperature.

Pelleting Seed

Some seeds are sold with a clay coating so that the seed appears like a uniform sized ball. The idea behind pelleting is that tiny seeds may be handled accurately (particularly by seed sowing machinery) and that irregularshaped seeds may be rounded sufficiently that they may be handled accurately by machinery.

Figure 28 Pelleted Seed of Begonia sp.

Often the contents of the pelleting material are proprietary, but the pellet is usually composed of clay, along with fungicide or insecticide and even some fertiliser.

Because of this coating, pelleted seeds often require moister conditions to germinate. The pellet coating must be fully imbibed before it breaks down – and it must break down before the seed within it may germinate.

Often commercial growers find that the germination percentage of pelleted seeds is slightly lower than that of unpelleted seed. However, the ability to accurately sow seeds at the desired density (particularly the very fine seed of Begonia spp.) more than compensates for the increased cost of the seed and the lower potential for germination.

There are limitations to the seed – for example, stratification of pelleted seed is not possible.

The British one penny coin used to give some idea of the size of the pelleted seed is 2cm in diameter.

Pelleted seeds of Begonia are available in packets for the home gardener. As small as these pellets appear, the seed is smaller still.


Seed Dusting and Coating

Seeds are often coated or dusted with treatments to prevent attack by disease organisms. Seeds that are sown in the cold, damp soils of early spring are particularly susceptible to rotting. In addition, the environment suitable for germinating seeds (warm, moist conditions) is also ideal growing conditions for some fungi. One of the major problems can be control of disease, especially 'Damping off'. Dampingoff may be due to Pythium spp., Phytophthora spp. and Rhizoctonia spp. – all are fungal diseasecausing organisms.

Any disease can have a devastating effect on the emerging seedling, as they are so weak and vulnerable. Dampingoff may occur at the preemergent stage, at the postemergent stage or in larger plants where it is termed root rot. Dampingoff will be covered in more detail later in this section.

Organic gardeners and growers may wish to avoid coated or dusted seeds. Some seed companies sell untreated seed that may be more vulnerable to rotting in cold, wet soils than treated seeds.

? Can you give an example of a seed dressing used on vegetable seeds?


Other Seed Treatments

The following table is not to be memorised for the RHS Level 2 Certificate in Horticulture examination. The information in this list is being provided to illustrate the scope of seed pretreatments only.

There are a myriad of treatments that may be used to encourage seeds to germinate. The following table is just a small sample.

Pregermination Treatment Seed Genus

Sown in Autumn Adonis Chill if no seedlings appear in 3 months Adonis Prechill sow in Spring Androsace Presoak Alstroemeria Seeds take 30 to 90 days to germinate Actaea Seeds take more than 90 days Betula Leave seeds uncovered when sown Allium Barely cover seeds Anemone May need two chilling periods to break dormancy Alnus Keep moist and dark Cyclamen


Pregermination Treatment Seed Genus

Use limefree compost Erica May take over a year to germinate Acer Chilling may improve germination Chaenomeles May take two winters to germinate Euonymus Sow shallowly Colchicum Sow outside Colchicum Hot water treatment pour boiling water over the seed to promote germination

Glycyrrhiza

Cold stratify the seed: Place in the coldest part of the fridge – length of time in weeks (4 weeks)

Leucojum

Warm stratify the seed: Place seed in a reasonably warm position e.g. Airing cupboard. – length of time in weeks (4 weeks)

Sorbus

(In the case of Sorbus the warm treatment must precede a 12 week cold stratification.)

Dampingoff

Dampingoff is the single term used to describe underground, soil line, or crown rots of seedlings due to unknown causes. The term actually covers several soil borne diseases of plants and seed borne fungi.

Rhizoctonia root rot (Rhizoctonia solani) is a fungal disease, which causes damping off of seedlings and foot rot of cuttings. Infection occurs in warm to hot temperatures and moderate moisture levels. The fungus is found in all natural soils and can survive indefinitely. Infected plants often have slightly sunken lesions on the stem at or below the soil/compost line. Transfer of the fungi to the germination room or glasshouse is should be eliminated.

Pythium Root Rot (Pythium spp.) is similar to Rhizoctonia in that it causes damping off of seedlings and foot rot of cuttings. However, infection occurs in cool, wet, poorly drained soils and composts, and by overwatering. Infection results in wet odourless rots. When severe, the lower portion of the stem can become slimy and black. Usually, the soft to slimy rotted outer portion of the root can be easily separated from the inner core. Species of Pythium can survive for several years in soil and plant refuse.

Phytophthora root rot (Phytophthora spp.) is usually associated with root rots of established plants but are also involved in dampingoff. These species enter the root tips and cause a watersoaked brown to black rot similar to Pythium. These fungi survive indefinitely in soil and plant debris.

Black root rot (Thielaviopsis basicola) is a problem of established plants. It does not occur in strongly acid soils with a pH of 4.5 to 5.5. It usually infects the lateral roots where they just emerge from the taproot. The diseased area turns dark brown, and is quite dry. The fungi survive for 10 years or more in soil.


Symptoms of Dampingoff

Seeds may be infected as soon as moisture penetrates the seed coat or as the radicle begins to extend. The radicle or seed may rot immediately under the compost/soil surface (preemergence dampingoff). It results in a poor, uneven stand of seedlings that is often confused with low seed viability.

Cotyledons may break the soil surface only to whither and die or healthy looking seedlings may suddenly fall over (postemergence dampingoff). Infection results in lesions at or below the soil/compost line. The seedling will discolour or wilt suddenly, or simply collapse and die. Weak seedlings are especially susceptible to attack by one or more fungi when growing conditions are only slightly unfavourable. Dampingoff is easily confused with plant injury caused by insect feeding, excessive fertilisation, high levels of soluble salts, excessive heat or cold, excessive or insufficient soil moisture, or chemical toxicity in air or soil.

Figure 29 Damping Off

Control of Dampingoff Diseases

The best control of dampingoff is prevention. The following steps outline some preventative procedures used by professional growers:

1. Purchase disease free plants and seeds. 2. Use of fungicidal coatings on seeds, which will be direct sown out doors in cold

soils, such as corn and peas. The organic gardener will not usually consider treated seeds, but should consider other cultural procedures to prevent seed rotting. Later, in the section on sowing seeds in the open, these will be briefly covered.

3. Seed borne disease can also be avoided by soaking the seeds for 15 minutes in a dilute sodium hypochlorite solution (1:20 water) prior to sowing.

4. Use sterile, well drained soil media. 5. Maintain a pH at the low end of the average scale, i.e. 6.4 pH is less susceptible

to root rot than a pH of 7.5. 6. Seeds must not be covered more than 4 times the thickness of the seed. 7. Do not allow pots to stand in water as excess water cannot drain and the roots

will be starved for oxygen bringing all growth to a halt. 8. Avoid overcrowding and overfeeding of plants. It is important to maintain

constant levels of growth through proper lighting and complete control of the growing environment.

9. Disinfect tools and containers. 10. Provide constant air movement. Ideally, air should move freely 24 hours per

day, but not directly aimed at the plants. This helps the seedlings to aspirate.

This seedling has been removed from the soil and placed on its side. Note the thin section where the soil level would have been – this is one sign of damping off. The seedling has collapsed. The cotyledons and true leaf are wilted.


Fungicides may be applied as a soil drench after sowing. They may be incorporated into the soil before sowing as a dust. They can be sprayed in mist form on all seedlings as a precaution until they have been transplanted into individual pots. Once transplanted, only those seedlings known to be especially sensitive to dampingoff need be misted with fungicide daily until the first or second seed leaves have emerged. An organic gardener cannot use most fungicides, but there are cultural practices that may be used and these are outlined below. A home gardener may control dampingoff diseases by:

• the use of strict hygiene. All containers, trays and tools must be sterilised. • the use of only clean, sterilised compost • avoid sowing seeds too thickly • ensure adequate air circulation around seedlings • ensure composts do not become waterlogged.

Successful Seed Germination in a Protected Environment

Sowing of seeds within a protected environment gives much more control of the conditions under which the seed germinated. These protected environments include: within a greenhouse, on a windowsill inside the house, under lights inside the house.

A home gardener may maintain keep a close watch on the seedlings and control the levels of:

• light (critical for the germination of some seeds, essential for the healthy growth of seedlings),

• moisture (often watering the compost before sowing or immediately after sowing may be supply sufficient moisture until the seeds have germinated),

• heat (depending on the seeds being started, use of a heated propagator may help improve the germination rate – though the use of a warm location within the house or greenhouse is an alternative).

The basic steps involved are: • Choose an appropriate compost and container • Sow the seeds • Provide appropriate conditions for germination (warm, cool, light, or dark) • Prickout seedlings • Grow on • Harden off

SeedStarting Media

Seeds started under glass or indoors require a compost that will provide the basic germination environment. The compost must retain moisture while still providing adequate aeration to the germinating seed. The compost must be loose enough that the seed’s radicle may easily penetrate and that the plumule may emerge without damage or delay. The compost must be sterile so that diseasecausing organisms are not present (these include those organisms that cause Dampingoff).

Often seed starting composts are very fine in texture and have a higher organic material composition. This ensures good contact between the compost and the seed and adequate moisture retention for the imbibing seed.


There are a number of alternatives available to the home gardener: • Seed composts (either loambased or loamless, with or without peat), • Peat pellets (for example Jiffy 7s), • Peatless pellets for the organic gardener (for example, Coir7s).

Composts

There are advantages and disadvantages to using loambased composts. Make a point of finding out about these and make a note of them.

Lesson 7 covers growing composts, both loambased and loamless.

The home gardener may consider either purchasing a readymade seed starting compost or may consider making the compost from its components. Usually, on a small scale, it is easier to purchase a readymade mixture, because this will ensure consistency and appropriate qualities of the compost. On a commercial scale, where the equipment for sterilisation, screening and mixing are costjustified, a grower may consider the value of preparing the compost on site.

In general, the composition of a seed starting compost may include any of the following ingredients:

• Loam The loam selected is usually medium to heavy turf loam that was stacked with strawy manure for six months. Any nutrient deficiencies would have been corrected by adding the appropriate amendments. The loam will have been sterilised (often by steam). The pH is usually slightly acidic (often around 6.3) and the loam is screened through a 9mm sieve to ensure large particles are removed. Loam contributes a source of nutrients, an ability to retain nutrients against the forces of leaching and the ability to buffer sudden changes in soil pH.

• Peat or peatsubstitutes Both peat and coir permit the retention of moisture within the compost. When peat is used, it is usually a granulated moss peat with a pH of between 4.0 and 4.5 and sifted as identified for loam. Substitutes of peat for seed composts include coir, leaf mould and composted garden waste. As the peat free initiative gains momentum, more proprietary peatfree seed mixes will become readily available.

• Sand or grit Sand must have been washed to ensure it is free from lime or chalk. Usually the sand selected is sharp and coarse with between 60 and 70% of the particles between 1.5 and 3mm in size. Sand adds to aeration drainage (preventing waterlogging and ensuring the seed receives the appropriate balance of moisture and oxygen).


• Perlite Perlite is an aluminosilicate of volcanic origin. It is the product of a process that involves crushing and rapidly heating (1000 o C) of the mineral material. Perlite is a white, lightweight, stable aggregate. In a seed compost, it provides good aeration, some moisture retention but contributes little nutrition. It is available in several grades: from supercoarse to superfine. Perlite has a wide range of uses outside of seed starting composts, and these will be outlined in lesson 7.

Figure 30 A Small Sample of Perlite

• Vermiculite Although less frequently used in seed composts, vermiculite provides many of the same qualities as perlite. Vermiculute is an aluminium, iron, magnesium silicate that has also been treated at high temperature to produce flakes of material (each containing thousands of tiny air cells). It is sterile, light and improves drainage and aeration. Unlike stable perlite, the platelike scales can break down in two years or less. This limits its use to shorterterm composts. Again, this product is used in a wide range of horticultural situations and will be described in more detail in lesson 7.

Figure 31 A Small Sample of Vermiculite

Loam Composts

Loam composts are composed of loam, peat and sand (or grit) – the relative proportion may be slightly different in different proprietary mixes.


One available premixed seed starting compost is called the John Innes ∗ Seed Compost (JIS) which is composed of:

• by volume: o 2 parts loam o 1 part peat o 1 part sand or grit

• plus the following amendments (per cubic metre of mix): o 1.10 kg superphosphate o 550 g chalk or ground limestone

Loamless Compost

Because quality loam is scarce, a number of composts that do not contain loam have been developed. These have become more widely used.

? Can you think of other reasons why this is?


Loamless compostsmay be "peat and sand" based or may include other materials.

The Glasshouse Crops Research Institute has formulated a number of composts. One recommended for seed starting has the following ingredients:

• by volume: o 50% peat o 50% sand

• amendments, at kg/m 3 : o potassium nitrate 0.4 o normal superphosphate 0.75 o ground limestone or chalk 3.0

The resulting composts are relatively low in soluble nitrogen (when compared to other formulations for other uses). Because of the length of time a growing seedling will reside in the compost, this lower nitrogen is quite acceptable.

Peatless Composts

Because both of the above composts contain peat as a main ingredient, the organic gardener would have to find another seed starting compost mixture. A number of larger manufacturers are now producing peatfree alternatives for seed starting. Although at the time of writing (January 2005), these may be difficult to find at a garden centre.

The HDRA (Henry Doubleday Research Association) has some peatfree compost recipes on their web site www.hdra.org.uk.

∗ As a result of research carried out commencing in the 1930s, the John Innes Horticultural Institute has produced a number of loambased composts. This is covered in more detail in lesson 7.


Seed Starting Pellets

An alternative to using loose composts in containers is to use pellets. One common pellet is the peatbased Jiffy 7. These pellets consist of a compressed peat disc surrounded by a degradable mesh cover.

When moistened with water, the peat disc expands and remains enclosed within the mesh cover. These pellets may then be placed into a tray and the seeds inserted into the opening in the mesh (that indicates the “top” of the pellet). The seedlings may grow on in this pellet until ready for planting out.

Figure 32 PeatBased Jiffy 7

Because of the growing concern of some gardeners and growers about the use of peat, a peatfree alternative has been produced. These Coir7smay not be widely available, although it is anticipated that they will become more readily available as demand for them increases.

Containers for Seed Sowing

Under glass or indoors, seeds may be sown in a number of different containers.

The most commonly used include:

• trays The traditional approach to seed sowing has been to fill a tray to the rim with compost, firm the compost (so that there are no large cavities within the compost to prevent the movement of water and to encourage root dryness), and then sow the seeds (covering the seeds if necessary). After the seeds have germinated and reached some size, they are pricked out and grown on in separate containers.

Trays may be stacked after sowing (this permits the more economical use of space), as long as each tray has a glass cover. This may only occur before the seeds have commenced germination – at that time they must be removed from the stack so that the seedlings develop in full light.

• pots or pans Pots are frequently used for seed starting. The most common today are plastic pots, although clay pots may also be used. Pots come in different sizes and depths. Standard pots are as wide as they are deep. Half pots are between one half to twothirds the depth of a standard pot. Pans are about one third the depth of a standard pot. All of these containers are suitable for starting seed and for growing seedlings on. However one consideration for the home gardener is the depth of compost these containers require and the amount of

A dry Jiffy7 in the compressed state.

A moist Jiffy7 in the expanded state.

Note the mesh surrounding the peat and the opening at the top of the pellet.


compost the seedling requires. Clearly, containers used for large seeds or seeds producing a deep root system quickly will need a considerable depth of compost to germinate in. However, smaller seeds with shallower root systems being germinated only in the pot (and transplanted elsewhere for growing on) may not require such a deep pot.

• peat pots or peatfree pots Peat pots and peatfree pots may be used for either sowing of seed or for potting on transplants. The advantage of these pots is that they may be planted directly into the garden, once the time for planting out has arrived. This may avoid some root disturbance that may occur if reusable containers are involved.

Traditionally, these pots have been made of peat. However, new coir pots may be found that may be used when peat is not desirable.

• paper pots and paper grow tubes Paper containers provide the same advantages and disadvantages as peat. These pots are made of some combination of degradable fibres (the precise content is proprietary) and are slightly less expensive than peat pots.

Paper tubes do not have a bottom. They are intended for taprooted seedlings – particularly sweet pea seedlings (and these are sometimes called sweet pea tubes). Unlike other containers, these tubes are used primarily for the direct sowing of seed in a suitable compost. The tubes take up relatively little space in a tray for germination and growing on.

Figure 33 Degradable Containers For Seed Starting

• module trays Module trays are used more frequently for commercial growing operations. Module trays come in a wide range of sizes – from more than 500 “cells” per tray to only a dozen or so cells.

Figure 34 Module Tray

From left to right: • Jiffy Pot made of peat • Paper fibre Grow Pot • Paper fibre Grow Tube


The smaller modules are intended for growing of seedlings for only a short time – the contents of the entire cell may be potted up (this permits automation of the potting up process as well as presenting little root disturbance during potting up). Larger cells are used when the seedling will remain in the tray for a longer period of time or when large seeds are sown.

• specialised modules (like root trainers) Root trainers are plastic cells, each of which is hinged at the base. These containers encourage deep root growth through the grooves within the cell that direct developing roots downwards. The hinged feature permits the seedling to be removed with reduced disturbance.

• containers from recycled household material Some home gardeners may find that they may be able to recycle some household waste for use as containers for seed starting. One example is the plastic milk jug – once thoroughly cleaned, the top may be cut away and holes bored into the base (to permit drainage) and these containers may be used to start seeds.

The main points to remember about container selection are the following: • the container must be sterile (if reusing containers from previous years, a good

washing with a dilute horticultural disinfectant, followed by a thorough rinsing in clean water and drying is necessary to prevent contamination of the new compost with diseases from previous years),

• the container must be of adequate depth to support the seedling for the length of time the seedling will grow in it before transplanting up,

• the container must have adequate drainage holes to permit excess water to drain from the compost – if the compost remains waterlogged, seeds will rot,

• the container is of a suitable size for the propagating environment (for example, it fits within the heated propagator, on the window sill, within the shelves of the airing cupboard) and for the number of seeds to be sown.

Sowing and Aftercare of Seeds Sown In Containers

When to Sow

The first step in sowing seeds is to decide when is the most suitable time. Sowing indoors too early may lead to spindly seedlings that have languished indoors too long. Sowing indoors too late may lead to delayed planting in the garden. In general, it is best to be too late than too early. Often the seed packets or gardening books will provide a range of seeding dates (for example, Begonia seeds should be started between the start of January to the middle of March). In a home gardening situation, with or without a heated greenhouse, the better time to start these seeds might be from the middle of February to middle of March or even later.

If you maintain a garden or seeding journal, you may consider writing the dates of seed sowing and transplanting in this journal. Then, as the season progresses, you may wish to make comments about your choice of dates. This will be a guideline to help refine the timing for your seed sowing next year.

The dates for sowing seeds will be staggered – some species require longer times before planting out and others require shorter times. It might be possible that you will start some seeds indoors in the middle of February, while others will be started indoors


in the middle of April. It is important to carefully plan how many seeds to sow – taking into account how much space they will require once potted on.

How to Sow Seeds

Although the goal is the same (to sow seeds sufficiently thinly that the seeds may develop successfully and are able to be transplanted without excessive disturbance), the techniques vary depending on the sizes of the seed:

First, prepare the container by filling with compost: • Overfill a suitable container with compost, firm slightly with the fingers (and ensure

that the corners of the container are filled adequately, in the case of a square tray). Tap the container to remove any large air pockets.

• Scrape off any excess compost with a board or straight edge. • Firm (slightly) the compost in the container – use a presser board or the bottom of a

similarsized container. This should leave the top of the compost about ½ to 1½ cm below the top of the container.

The container may be watered at this point. One technique was illustrated and described on page 40. The other alternative is to water from above using a watering can with a fine watering rose. Once the compost is moist, permit the container to drain.

Then prepare the seeds for sowing.

For very large seeds, consider sowing into individual pots or peat pellets.

For large seeds (and pelleted seeds), space each seed individually on the top of the compost. Space the seeds evenly over the surface of the compost. Use the spacing identified on the packet. When in doubt, seeds are often spaced in proportion to their size – leaving sufficient room for the seedling to develop without interference from neighbouring seedlings and enabling the prickingout process to proceed without too much disturbance of the roots. Larger seeds (like those of Dahlia) might be spaced at 1 to 2 cm apart.

For medium seeds, scatter the seeds over the surface of the compost. Ensure that the seeds are not sown too thickly. Seeds may be sown directly from the packet, your palm or from the fold of a piece of paper. Usually, sowing from the packet takes more practice than the other techniques to distribute the seeds evenly.

For small seeds, mix the seeds with a small amount of silver sand (that is, sand with the iron oxides washed out that is low in lime and salts). Then scatter the entire mixture thinly over the compost surface.

In general, do not cover pelleted seeds or very fine seeds. Other seeds may be covered with a layer of compost about ½ cm deep (again, it is usually better to err on the side of too little compost than too much). Another choice is to cover the seeds with a thin layer of fine vermiculite – this permits air and light to reach the seeds and also reduces the risk of dampingoff (about ½ cm of vermiculite is sufficient).

The compost has to provide a suitable resting place. The ideal depth of sowing is important because at this position the seed is held adequately so that the thrust of the radicle is contained without dislodging the seed. Also the energy of the germinating


seed is not dissipated in the etiolation of the epicotyl (or hypocotyl in some seeds) as it grows through too great a depth of "earth" cover.

To ensure adequate contact between the seeds and the compost, the surface may be pressed down slightly with an empty container. In general, do not do this for pelleted seed. Never press moist compost too firmly – seeds desire a fairly loose medium but one without large air cavities.

Prepare a label – identify the date and cultivar sown. There is a technique used for writing labels that is used by professional propagators:

• The information is written on the tag so that the start of the species name and cultivar will appear above the compost level once the label is inserted.

Figure 35 Label Writing

• If the label is written the other way around, then once inserted into the compost, all that might be seen is “Gems” and this might not be enough to identify the seedlings at a glance (as a result, removing the label might be necessary to read it – and this might cause disturbances to the seedlings).

After sowing the seeds, water them if the compost was not watered before sowing. If the covering compost is dry and container has already been watered, moisten the covering compost using a mistsprayer.

Then cover the container to maintain humidity levels in the compost. The traditional way is to cover the pot or tray with a sheet of clean glass. Another alternative is to place the container in a covered propagator or cover with a plastic dome. A final option is to enclose the container within a polythene bag or cover with cling film.

Figure 36 Methods of Seed Sowing Sowing in Pans or Pots

Place the container in a suitable location – in light or darkness, in warmth or cool conditions. In general, seed packets are the best source of information about germination temperatures. Do not place the covered container in very bright light or direct sun – this may cause the seedlings to overheat and die.

label date and cultivar

glass, paper or polythene cover

thin compost covering seeds

a suitable compost, e.g. organic multipurpose compost

no need for crocks in plastic pots with ample drainage holes

Begonia ‘Devon Gems‛ February 20, 2005


Sowing Seeds of Hardy Plants

The technique described above is suitable for starting many annuals, biennials and perennial seeds. However, some seeds will remain a long time in the seed starting compost before germination begins. For example, the seeds of many woody plants, alpines and some perennials require a long exposure to appropriate conditions before germination will commence.

These seeds require slightly different treatments. All the steps up to and including seed sowing remain the same (prepare clean equipment, fill with compost, press the compost down and sow the seeds). However some differences do exist:

• The compost usually has a higher percentage of grit or sand to provide better drainage.

• The seeds are covered with a thin layer of horticultural sand or grit. This is preferred because it helps prevent the growth of mosses and liverworts, helps preserve the compost moisture and does not break down with time. It also will not blow away when exposed to the elements. This covering also prevents the seeds and compost below from being washed out by heavy rains.

• The seeded containers are not covered with plastic or glass. They are placed outside, in a shaded location. Often a cold frame is a good location.

For example, most Mediterranean species germinate in the autumn after the first rain. This works well with the mild winters but for the UK climate, sowing hardy species in the very early part of the year and standing them outside to take the chill of winter has much to commend it. Glass frame lights with their increased warmth could go on in early April.

A useful system is to use 90mm plastic half pots of good quality (not every seed pan will germinate in the first spring).

Figure 37 Methods of Sowing – Hardy Perennial seed

This system provides the essential conditions for germination for the viable seed. The main ones are adequate warmth (for hardy plants), moisture, oxygen, light for lightrequiring species and dark for those with a dark requirement.

Light for the seedlings after emergence, a suitable restingplace, relative freedom from pests, diseases and weeds plus a relatively low competition for water from the soluble salt concentration in the compost are the others.

label and date

12mm layer of pea grit (sized approx. 6mm to 9.5mm) over seed layer

plastic pot (special crocks unnecessary)

Mypex or capillary matting


Pricking Out and Potting Up

Once the seedlings start to appear, any covering should be removed from the container – this includes the glass or plastic cover or the lid from the propagating unit.

At this point, the ideal location would be to place the seedlings in a heated greenhouse, but using lights indoors or a bright windowsill is often an adequate substitute. The seedlings need strong light, but should not yet receive full sunlight. The moisture levels of the container should be checked frequently to ensure that the compost has not dried. Any reduction in compost moisture at this point may “check” (that is, delay) or kill the seedlings. However, the compost should never be so wet that the roots do not receive sufficient oxygen. The key is to keep the compost moist but not wet.

After a time, the seedlings will be large enough to prick out and transfer to other containers for growing on. The seedlings must be removed from their original containers before they become so crowed that there is little room to develop adequate but after they have reached sufficient size that transferring them is possible.

Figure 38 Seedlings of Primula reidii var. williamsii Grown in Modular Tray

These seedlings of Primula reidii var. williamsii are the result of seeds that were sown directly into the modular or cellular tray in February. The seeded trays were then placed into a cold glasshouse, because Primula seeds prefer to germinate in cold conditions. Germination took about 4 weeks. This photograph of the seedlings was taken in July.

Potting Composts

This step requires a potting compost to act as the growing media for the seedlings. A potting compost may be loambased or loamfree, it may contain peat or peat substitutes.

Potting composts usually have a slightly coarser texture than seeding composts. They usually also contain some fertiliser.


The John Innes loambased compost (called J.I. Potting No. 1) consists of: • 7 parts screened sterilised loam • 3 parts peat • 2 parts grit • to each cubic metre of this mixture, the following amendments are added:

o 1 kg hoof and horn (which supplies nitrogen) o 1 kg superphosphate (which supplies phosphorus) o 0.5 kg potassium sulphate (which supplies potassium) o 0.5 kg calcium carbonate (to neutralise the acidity of the peat).

Loamless composts are also formulated for potting up of seedlings. The Glasshouse Crops Research Institute has developed a number of composts including:

GCRI Potting Composts General Use Winter Summer High P (for

longer term use)

Peat:sand ratio 75:25 (by volume) Amendments at kg/m 3 :

Ammonium nitrate 0.4 0.2 Urea formaldehyde 0.5 1.0 Magnesium ammonium phosphate

1.5

Potassium nitrate 0.75 0.75 0.75 0.4 Normal superphosphate 1.5 1.5 1.5 Ground chalk or limestone 2.25 2.25 2.25 2.25. Ground magnesium limestone 2.25 2.25 2.25 2.25 Fritted trace elements (WM 225)

0.4 0.4 0.4 0.4

Peatfree alternatives also exist. Proprietary ones may be purchased through some garden centres (although availability may be limited). The HRDA web site (www.hdra.org.uk) identifies a number of different recipes that the home gardener may wish to consider.

As with all composts used for potting on, the compost must provide a suitable root environment (adequate moisture retention and adequate drainage) and a source of nutrients for the growing seedling.

More details about composts may be found in lesson 7.

Pricking Out and Potting Up Procedure

The procedure for pricking out involves the following basic steps:

1. prepare the containers for planting up

If using reusable containers, these should be sterilized (or new). Containers should be filled with a potting compost (again, sterilized) and firmed down so that the top of the compost is about ½ cm below the surface of the container.


2. moisten the compost of the container with the seedlings, permit the water to drain

3. tap the seedling container so that the compost is loosened a little from the edges (this makes lifting the seedling with the compost “ball” around its roots a little easier)

4. by gently holding the seedling by a leaf (or expanded cotyledon) and carefully inserting a widger or small dibber underneath the root system, lift the seedling – trying to retain as much of the seedling’s root as possible

Figure 39 Widgers and Dibbers

Never hold the seedling by the stem. As gentle as you might be, the stem is easily damaged while the seed leaves or true leaves tolerate handling much better.

Figure 40 Seedling Ready to Transplant

5. in the potting compost, make a small hole or depression with the widger or dibber (of sufficient size to house the root of the seedling)

6. carefully “drop” the seedling root ball into this hole and gently firm the compost around the roots

7. water the seedlings carefully – this helps remove large air cavities that may have been created by the insertion of the seedling and ensures adequate contact between the roots and the compost

Continue with all the seedlings. Space them sufficiently that they have room to grow (perhaps 4 to 5 cm apart) if transplanting to a tray. Place them in an appropriatesized

dibber metal and plastic widgers


container if transplanting them to individual containers.

More experienced gardeners grade their seedlings – transplanting similarsized seedlings together so that smaller seedlings are placed together. This permits smaller seedlings to grow unaffected by the competition that the greater vigour of the larger seedlings tends to produce. Unless growing a species where the weaker seedlings produce the more desirable plants, transplant up the healthier seedlings and discard the weaker seedlings. An example of an exception to this rule is for certain strains of Stock, Matthiola incana. The yellowishgreen coloured seedlings (which produce the desirable double flowered forms) are potted up while the darkgreen coloured seedlings (which produce less desirable single flowered forms) are discarded.

Ideally, seedlings are only potted on once before they are placed in their final growing location (whether that is within a bed or a container). However, if the transplanted seedlings require further potting on to prevent crowding, then there is nothing wrong with transplanting up again. The balance between container size and space must be determined by each gardener. Often space is in short supply during the late winter and early spring months, so smaller containers are used to permit the growing on of more seedlings. However, these seedlings may start to become crowded later in the spring and may require potting up again. It is usually better for the seedling to be potted up into a container that is not excessively big. The compost conditions in smaller containers is often more suited to the needs of the smaller root systems of the seedlings.

The containers of potted up seedlings should be placed in a location where they can grow on. Light levels should normally be as high as possible without being so high that they scorch or damage the transplant. Initially slightly higher temperatures may help the transplant reestablish. Ultimately, lower growing temperatures (although not freezing temperatures) may help produce sturdier plants.

Depending on how long the seedlings will grow on before they are planted out, it might be necessary to fertilise the seedlings. Usually, a generalpurpose fertiliser or organic feed is applied (often at weak concentration – to ensure that the young roots are not burned and that the salt concentration in the compost remains low).

Hardening Off

Before planting into the garden, seedlings require a period of adjustment to the higher light levels, effects of the wind, and varying moisture levels of the soil. This process is called “hardening off”.

This process must occur gradually – generally over a period of up to six weeks or so before planting out.

Slowly the temperatures that the seedlings are enjoying must be lowered. Watering will also become less frequent – never letting the seedlings wilt, but waiting until the moisture levels in the compost are lower than they have been previously. And seedlings must gradually be introduced to higher light levels – this is especially true of seedlings being grown indoors.

A cold frame is an ideal site for hardening off – gradually opening the lights a little each day so that the inside temperatures become cooler and the seedlings experience a little more wind disturbance.


A gradual process of hardening off prevents or limits the growth check that would occur if seedlings were subjected to the harsher environment outdoors suddenly.

Germinating Seeds in the Open

Sowing seed directly in the garden is an option for many hardy annuals, biennials, perennials and vegetable seed. Hardy annuals are usually sown where they are to flower, root vegetables are sown where they will grow to maturity and biennials and perennials are often sown in nursery beds where they will grow before being planted out into the beds and borders of the garden.

There are two main methods of sowing seed directly in the garden broadcast seeding and sowing seeds in drills.

In both cases, prepare the soil well. It is best to wait until soil has dried before starting to prepare the soil – this minimizes the risk of damaging the soil structure.

If the soil is lacking in nutrients (often a soil test is the only way of knowing this), add amendments at this time. For example, a preplant incorporation of a balance fertiliser (for example Growmore 777) or the organic alternative (Fish, blood and bone) would be appropriate at this time, if these nutrient deficiencies were not addressed the previous autumn. Lightly rake or fork the fertiliser into the top few centimetres of the bed. Organic gardeners tend to look after their soil – its depth, structure and water holding capacity by using manures and composts. These tend to maintain nutrient levels.

The environment for successfully starting seeds in the open does not vary greatly from that in a protected environment. Seeds need warmth, light, oxygen and moisture. However, what is different between the open and a protected environment is the degree of control that the gardener has on these conditions.

The question of temperature can be dealt with by ensuring that seeds are started at the right time. If the soil is to be warm, a gardener may speed this process by using a black plastic mulch. Placed on the ground a few weeks before sowing seed (or planting seedlings grown elsewhere), the soil may be warmed early.

Moisture levels may also be controlled somewhat by the gardener. For small locations in a dry year, periodic watering with a watering can may be sufficient. There is a wide range of irrigation equipment that may be used in larger situations – from sprinklers to seeping hoses.

Light levels should be adequate in the site chosen. Plants requiring full sun should probably not be sown in a shady location. Plants requiring some shade should not be sown in an exposed, sunny location.


Broadcast Seeding

Broadcast seeding is occasionally the most appropriate for direct sowing of annuals (and sometimes biennials and perennials). This is the best method for sowing between existing plants – for example, within an established border.

Weeding may be more difficult, because the seeds and weed seeds will both germinate but using a hoe to eliminate the weeds without affecting the desired seedlings is difficult. When the seedlings are not in rows, hand weeding may be necessary.

The basic steps are:

1. Bring the soil up to field capacity – if it is at all dry – then let the sticky wet condition dry.

2. Prepare the beds to a fine tilth – on the last pass, rake the entire bed in one direction.

3. Scatter the seeds as thinly and evenly as possible – there are a number of techniques possible and equipment that might help (for example, a seed sower)

Mixing the seeds with silver sand before broadcasting the entire mixture is one alternative that helps distribute fine seed evenly.

4. Ensure that there is adequate seed/soil contact by raking the area in a direction at right angles to the last pass of the rake before sowing. Seeds sown in drills can be firmed by treading down the row before the final rake over.

5. Label the seeds (and water in well, if the step 1 was not possible).

Sowing Seed in Drills

A drill is a narrow furrow that is made in the soil for the purpose of sowing seeds.

Sowing seeds in drills is appropriate for sowing: • vegetable seed (i.e. turnips and onions – or for brassicas and leek seed beds), • annual seed – for example, in cut flower beds, • biennial seed and perennial seed – for nursery beds.

The advantage of sowing seed in a drill is that the seeds are easier to weed (particularly, they are easier to distinguish because weeds seldom germinate in straight rows).

The basic steps are:

1. establish where the rows of plants are to be – the spacing between rows is critical since it must be large enough to permit the plants to grow adequately and to permit cultivation between rows, but it should not be so large that space is wasted in the garden

At this time, determine how much seed is to be sown. There are two approaches – calculate the number of plants that may be grown in the area


allocated (using the plant size and seed packet information to determine how much room each mature plant requires), or calculate the number of plants desired, determine the amount of space this requires. Seed more than the desired number of plants because there will be some losses between sowing and harvesting.

2. use a garden line to establish a straight line

If rows are short, a faster alternative is to use the straight handle of a rake or hoe or even a straight cane. Pressing this lightly into the soil surface will establish a straight row as well as prepare a shallow drill.

3. using the corner of a hoe or a trowel, draw down the line established by the garden line

This process produced a “v” shaped trench in the soil – the drill.

Figure 41 Drill For Sowing Seeds

The depth of this drill is determined by the planting depth of the seed. Larger seed is usually sown deeper than smaller seed. Usually drills are not deeper than 2 to 3 cm. The most important point is that the drill should be of uniform depth for the entire row – this ensures that the seeds are sown at equal depth, so germination will be uniform.

Drills in heavy (clay) soils are usually shallower. Drills in light (sandy) soils are usually deeper.

If the soil is very dry, water the drill before sowing the seed. If the soil is very wet (although this is not an ideal time for working the soil, sometimes the schedule dictates that this happen), put a shallow layer of dry sand in the bottom of the drill before sowing the seed this will help keep the seed from rotting in the cool, wet soil.

4. sow the seed in the drill – space the seed as evenly as possible

5. fill in the drill to cover the seed, firm the soil and water if necessary

At this stage, it might be necessary to determine if the seedbed requires protection from rabbits and birds. If so, now is the time to put down deterrents –

A hoe being used to draw down a garden line to establish a “V” shaped drill.

Garden line acting as a guide for the hoe.


this may simply be the use of a wire mesh over the seedbed area that will keep diggers at bay until the seeds emerge. Then the mesh should be removed to avoid causing problems for the seedling growth.

6. monitor the seeded area to ensure that sufficient moisture remains in the seed bed – water when necessary

Thinning Seedlings

Once the seeds have started to germinate, it may become clear that the seedlings need to be thinned. Thinning helps ensure that the seedlings are spaced adequately that the ones remaining have room to grow and develop normally. If seedlings are left growing in crowded conditions, then they will compete with each other for space, moisture and nutrients. The result will be weak, spindly growth. There are two methods used to thin the seedlings:

• carefully transplant the seedling from an area of too many seedlings to an area of too few seedlings (a widger is helpful in doing this) – try to avoid disturbing the existing seedlings when doing this

• for seedlings that are very thickly sown, it is often best to pinch off or snip out the undesired seedling at the soil surface – this will prevent disturbance of the remaining seedlings (if using this method, be sure to remove and compost any undesired seedlings – leaving them on the soil’s surface may entice pests to the crop plants).

Always try and grow a few spare to swap but to try and grow all that may come up could be a selfinflicted disaster.

Check your understanding so far …

What is meant by 'seed dormancy'?

What is the first stage of seed germination?

What is the importance of oxygen for seeds, and how do we ensure their oxygen needs are met?

Why is the correct sowing depth important?

What is stratification?

What are the seed's main competitors?

Check your responses against the lesson text.


? Answer to Self Check Question from page 39

Which of the following would rapidly kill germinating seed, and why? • excess moisture • excess air/oxygen • excess heat

Excess water would cut off the oxygen supply. Air that is too dry will quickly desiccate the seeds, and too high a temperature will scorch leaves and stop photosynthesis because of damage to the leaf cells and excessive water loss.


Can you give an example of a seed dressing used on vegetable seeds?

Examples of seed dressings used on vegetable seeds are hard to find currently because of the pesticide regulations:

1. Deltamethrin Is a pyrethroid insecticide with contact and residual activity and is available to professional growers as a micropearl for control of flea beetle in broccoli, Brussels sprouts, cabbages, cauliflower, swedes and turnips.

2. Pea seed can be treated with thiram against foot rot diseases, although this seed may not be available to amateur gardeners.


Can you identify why loamless composts have become more widely used?

Loamless composts have become more widely used because they have the following qualities:

• they are lighter to handle • they may be cleaner (fewer pest and disease problems). • Gardeners and growers can generally be assured they are of a

standard quality. JI composts have become very variable.

Because the loam ingredient has become scarce, the cost of producing these composts has increased.


3 FACTORS INFLUENCING PROPAGATION BY CUTTINGS

By the end of this section, you will be able to demonstrate an understanding of the factors which influence successful propagation by cuttings:

• State the role of physiological factors upon the speed and success of rooting of cuttings.

Introduction

Vegetative plant propagation includes all plant production techniques that utilise any part of a plant not associated with flowering, i.e. roots, stems, and leaves.

One group of vegetative propagation techniques involves the use of cuttings to produce new plants. Cuttings may be taken from the stem, the leaf or the root.

The use of stem cuttings is the most popular method of vegetative propagation – used by both commercial growers and by home gardeners. However, some home gardeners may already be familiar with the use of leaf cuttings to establish new houseplants (for example, African violets, Saintpaulia spp., are frequently propagated by leaf petiole cuttings). And gardeners who have battled with dandelion weeds (Taraxacum officinalis) may already be familiar with propagation by root cuttings – since leaving even the smallest piece of root in the soil often results in the growth of a new dandelion plant.

Of all the aspects of propagation by cuttings, the most difficult one is how to keep the cutting alive until new roots and shoots are formed, and the cutting has developed into a new, independent plant. There are steps that a gardener/grower may take to speed up these natural processes.

The basic steps (and sequence) in the propagation process are:

Choice of appropriate plant material ê

Treatment of plant material ê

Manipulation of conditions for regeneration ê

Secure subsistence of plant material (stay alive) ê

Establishment of new plant


The Physiology of Propagation by Cuttings

Before we discuss the factors that influence the successful propagation via cuttings, a review of the physiology behind the use of cuttings is essential.

Propagation through cuttings exploits the plant’s natural ability to produce roots and shoots from pieces of a plant to permit, eventually, the generation an entirely new plant (this is called totipotency). Not all plants are capable of being propagated by cuttings. Even those plants that are capable of being propagated by cuttings may only be propagated using stem cuttings or leaf cuttings or root cuttings. It is a rare plant that may be propagated by all of these methods.

Some plant material has the greater capacity for regeneration – and the choice of cutting material uses this difference in ability to speed the process. For example, the juvenility of the cutting material may affect the speed (of even likelihood) of rooting. (The concept of juvenility was introduced in lesson 2.) The time of year and the type of material used are just some of the different issues involved.

For a cutting to develop into a new plant, the cutting has to do the following: • Stay alive (this means, absorb moisture and oxygen to permit respiration

processes to continue). • Heal the wound to prevent the entry of undesirables into the plant tissue and

to reduce the loss of water through the cut. • Produce adventitious roots to absorb water and minerals. • Produce adventitious shoots to develop new leaf material to increase

photosynthesis.

Cutting Anatomy

Anatomically, plant parts used in propagation must have the cellular potential to dedifferentiate ∗ and become meristematic.

The first priority of any cutting is to reestablish a structure to absorb water and minerals. Water is needed to replace any moisture lost via transpiration. Water and minerals will ultimately be required to fuel photosynthesis and respiration to permit growth.

The roots formed from a cutting are adventitious roots. They form from root initials that either already exist in a dormant state near the vascular tissue (near the cambium in woody plants or near the vascular bundles in the cortex of herbaceous plants) or form near this tissue. Preformed root initials can be found in easily rooted plants such as willow and poplar. Advantage is taken of preformed root initials in these species when the technique of hardwood cuttings is used. These preformed root initials develop naturally and may appear as aerial roots in humid environments.

Root initials can develop into root buds and eventually break through the epidermis to emerge from the cutting. When the new root emerges, it is fully formed – with root cap and vascular tissue that connects with the vascular tissue of the cutting.

∗ The process of dedifferentiation involves the ability of mature cells to return to a meristematic state – that is, to lose specific function and return to the simple cells that can develop into new cells.


In some plants, a ring of tough sclerenchyma cells may present a barrier to the root bud – in this case, wounding of the cutting may break up the sclerenchyma barrier to permit the root to emerge.

HERBACEOUS PLANT

ROSE CHRYSANTH' CARNATION

Days for root initiation

8 to 12 days 7 days 3 days 5 days

Days for root emergence

21 to 28 days 21 days 10 days 21 days

Origin of root initials

Outside of but between vascular bundles

Young secondary phloem

Interfascicular region

Inside a fibre sheath roots emerge from cutting base

Callus

When a cutting is placed in a suitable environment for rooting to occur, callus tissue develops at the cut end. This callus is a mass of parenchyma cells

The growth of callus at the cut base of a cutting is often independent of root formation but both require similar environmental circumstances. Callus is therefore seen as an appropriate activity of a healthy cutting and is likely to produce a good root system. The point of origin of callus growth is from vascular cambium.

Root emergence is influenced by the sort of callus growth develops. This, in turn, is influenced by pH of the rooting medium. When the rooting medium pH is around 6.0, callus is easily penetrated because the cells are large and not compact.

In order to heal the wound, the cambium cells have to divide and produce additional cells, which become the callus tissue. Callus tissue is the plant’s natural reaction to a wound – the intention is to prevent the entry of insects or disease into the exposed tissue and to prevent loss of moisture. To encourage this cell division, various steps can help:

1. Suitable cutting size, condition and selection A large surface area of the wound requires more effort to cover with callus than a slender cutting. But too thin a cutting means fewer stored food to provide the resources to enable the callus tissue to form.

2. Dunking in fungicide to reduce the "load" of disease inoculum. A reduction in the number of disease organisms present on the cutting tissue means fewer disease organisms may be present to penetrate into the cutting before the callus tissue has formed. This is not a suitable task for the organic gardener.

3. An ideal rooting mix compost very low in salt concentration and yet supplying ample water film and oxygen in the "soil" air. This is a suitable environment for cell growth – ensuring an adequate supply of moisture to the cutting.

4. Suitable basal and air temperatures it is the base of the cutting which needs the stimulation for cell division at this stage. Warmer temperatures mean cellular processes occur faster – this includes cell


division involved with the creation of callus tissue. Temperatures that are too warm will delay cellular division.

Figure 42 Cross Section of Young Deadnettle Stem

Physiology of Root Initiation

Plant hormones are naturally occurring organic chemical compounds which in very low concentrations coordinate physiological processes. They are used for communication between one part of the plant and another to bring about growth regulation. Unlike animal hormones that act on distant cells, plant hormones can act on adjacent cells as well as distant ones. Hormones are chemicals, which are released from one cell that affects growth and development of other cells and tissues.

strengthening cells

phloem cortex

When exposed as in cutting preparation the cambium may divide to form callus tissue of parenchyma cells – which heal the wound and may enable root initials to arise.

A new cell wall arises as the new cells are produced.

cambium cells dividing

cambium

vascular bundle

xylem vessel

parenchyma thin walled storage cells

phloem

cambium

xylem chloroplasts

epidermis


It is best to think of hormones as 'plant growth regulators'. Not all growth regulators are hormones.

Within the plant, the following naturallyoccurring plant growth regulators influence rooting:

• Auxins, • Cytokinins, • Gibberellins, • Abscisic acid, • Ethylene (This in minute concentrations acts as a plant hormone).

All of these substances were briefly introduced in lesson 2. Of these, however, it is auxin that plays the greatest role in rooting of cuttings.

Auxin

Auxin is produced in the shoot apical meristem tissue. Within the plant, auxin plays the following roles: 1. promotes cell elongation in stems i.e. stem growth. 2. promotes development of lateral roots, even at very low concentrations 3. may also participate in stem / root growth responses to light and gravity 4. inhibits lateral bud sprouting and therefore enhance apical dominance.

Indole acetic acid (IAA) is a naturally occurring auxin. This form of auxin is unstable and breaks down easily with exposure to sunlight and plant debris.

Auxin is involved in the very first step in the creation of adventitious roots. During this stage, auxin must be continually present. This auxin would naturally be supplied from the terminal bud. However, since the mid1930s, synthetic auxins have been available. Two of the most common are:

• indole butyric acid (IBA) and • naphthalene acetic acid (NAA).

IBA is the more commonly used synthetic auxin. It is widely applied in general use because it is stable and nontoxic to most plants over a wide concentration range and promotes root growth in a large number of plant species. Some softwood cuttings may have toxic reactions to IBA, which will lead to poor or no growth and mortality.

NAA is less widely used as a pure hormone. Usually mixtures of IBA and NAA promote root initiation better than either one alone. There is a synergistic effect. Both of these chemicals are available in talc or in liquid formulations.

The solubility of IBA in water is very slow and when applied to the basal end of a cutting a lot is lost as the cutting is inserted into the compost. The use of liquid hormones is becoming more widely accepted in the U.K.

Hormone rooting powders are not usually considered suitable to be used in an organic garden. There are now some commercially available organic substitutes (some are based on extracts from seaweed) and these may be effective. In additional, a second approach is to use a “rooting enhancer” sometimes called


“willow water” ∗ .

Auxins help with the rooting of cuttings in the following ways:

• Synthetic auxins help reduce the length of time required for adventitious roots to form. This is an important factor in the success of rooting cuttings, because the longer the cutting has to survive without the ability to absorb water and nutrients efficiently, the less chance the cutting has of surviving to produce roots and shoots.

• The percentage of rooted cuttings increases when synthetic auxins are applied. In fact, synthetic auxins help difficulttoroot cutting material form adventitious roots. In these cases, without the application of synthetic auxin to the cutting, the cutting would probably not produce roots before it deteriorated and died.

• Auxins also help improve the quantity and quality of roots produced.

The amount of auxin applied to the cutting is important, however. At too high a concentration, synthetic auxin applied can inhibit subsequent shoot growth.

Synthetic auxins can also be used in herbicides (an example is 2,4D), but not for the organic grower.

Figure 43 Rooting Hormone Visible on Bottom of Cutting

Cytokinin

Cytokinins are plant growth hormones that play a role in cell growth.

1. stimulates cell division in root meristems where they are abundant. 2. promotes sprouting of buds, in the correct balance. This is of obvious

importance in root cutting regeneration. 3. can promote leaf expansion and retard leaf ageing.

However, plant tissues with too much natural cytokinin may be more difficult to root than tissues with a lower cytokinin level.

∗ “Willow water” is an extract produced by soaking, in warm water, small greenwood cuttings taken from any willow (Salix spp.). Willows are one of the easiest woody plants to root (they readily form adventitious roots) and this is why the water containing extracts from the willow cuttings may help promote rooting in other species.

This cutting has an organic rooting stimulant, not a synthetic auxin.

These cuttings have been dipped in a synthetic auxin powder.


Gibberellins

Gibberellins are naturallyoccurring group of substances that play a role in the synthesis of proteins. In general, gibberellins can retard root formation when at too high a concentration. But they have a positive effect at low concentrations. Other roles of gibberellins in the plant include:

1. promote cell elongation and urge buds and seeds to break dormancy and resume growth in the spring.

2. stimulate the breakdown of starch and may influence flowering in some species.

Abscissic Acid (ABA)

Abscissic acid often acts as an inhibitor within plants. The role in root formation is not clearly understood. However abscissic acid, amongst others, reduces gibberellin activity and therefore promotes rooting.

Ethylene

Ethylene is a gas that is produced by plants and is often grouped with plant growth regulators even though it is not a hormone. Ethylene can promote root formation on stem and leaf tissues, at concentrations of about 10 parts per million.

In addition, ethylene plays a role in:

1. stimulation ripening of fruit and is used commercially for this purpose. 2. promotion "abscission" of leaves, fruit and flowers thereby causing them to drop

from plants at appropriate times of the year.

Selection of Cutting Material

The first step in the successful propagation from cuttings is to select appropriate plant material and the most suitable stage of growth from which to take the cutting.

Some cutting material has better potential to form adventitious roots and shoots. The important considerations in this choice are:

1. Select material with the genetic potential to regenerate (that is, produce adventitious roots and shoots). It should be true to type (the same variety).

2. Select material with the most suitable phase of growth (juvenile growth is usually best).

3. Select material with the most suitable nutritional state.

4. Select sturdy, healthy material – free from pests and diseases.

5. Take cuttings at the most appropriate time of year.

It is important that commercial growers use only the best forms and selections (that is, uptodate clones) and avoid propagating inferior stock. A home gardener,


however, is usually limited to which plants may be propagated by the availability of “stock” plants – these may be plants within the gardener’s own garden, the gardens of friends and neighbours or other sources.

Always select material that exhibits “normal” growth. Take cuttings from material with closely spaced nodes (not from material with abnormally widelyspaced nodes).

Figure 44 Spacing of Nodes

The goal is to choose the appropriate cutting material, of the appropriate age and condition, at the correct time of year that the rooting process or new shoot development will be the fastest. The sooner the cutting has established new roots and leaf area, the faster the new plant will be able to survive independently and the greater chance the new plant has of surviving.

Some conditioning of the stock plant prior to the taking of cuttings may help increase the rooting success rate. Many of these are suitable for the commercial grower, but some may be performed by the home gardener. These treatments include:

• etioliation • temperature manipulation

Genetic Potential

Some plants are not suitable for propagation by cuttings.

For example, a number of woody plants are not propagated by cuttings because these cuttings are unlikely to form adventitious roots. For example, the Dove tree, Davidia involucrata, (whose fruits were illustrated earlier in this lesson) are not propagated by cuttings.

Other plants root easily from cuttings, and no special care need to be taken when handling these cuttings. Some cuttings may be taken from the stock plants and then immediately planted outside. Willow (Salix spp.) are often within this second group.

Many plants fall between these two extremes. In these cases, some care will be required. The extra treatments that help root cuttings will be described in more detail later in this lesson.

Tightly spaced nodes Widely spaced

nodes


Juvenility

The phenomenon of juvenility is well known but the mechanism for influencing rooting in cuttings is still not well understood. In lesson 2, the concept of juvenility was introduced.

Usually juvenile cutting material is more likely to root faster than more mature cutting material. Cuttings taken from the most mature (and older) portions of a plant may be slow to develop adventitious roots. In some plants, mature growth will not form adventitious roots. However, cuttings taken from the juvenile phase may root quickly. Because it is important to develop roots quickly to ensure that the cutting remains alive to permit the formation of new shoots, speed of rooting is critical.

The ability of cuttings to produce adventitious roots declines as plant material ages. This is believed to be the result of the production of rooting inhibitors in more mature wood or the lowering of the amount of hormones that work with auxin to promote rooting in mature material. Propagules from juvenile growth will often root well while mature growth from the same plant will root less readily or not at all.

Growth in the juvenile condition is found in tissues:

1. Originating from young seedlings. 2. Arising from adventitious buds on stems. 3. Grafted onto young wood.

One of the qualities of juvenile tissue is that it does not produce flowers. Flower buds themselves may play a role in the reduction of rooting of cuttings.

In many plants, cuttings will root equally well when flowering or vegetative wood is used. However in plants that are difficult to root (such as some Vaccinium species), the use of wood entirely in the vegetative state is necessary. It is thought that flowering and the production of adventitious roots are antagonistic with regard to concentration of natural auxin levels. Removal of flower buds appears to accelerate rooting; this is probably related to auxin levels.

Apart from these effects it is normal practice to remove flower buds, as they are attractive sites for disease producing fungi such as Botrytis and can utilise stored carbohydrates if they continue to develop.

Stock plants may be kept in a juvenile state by regular pruning. This is often what commercial growers must do to maintain their plants in a condition that will permit the annual removal of cutting material for propagation. A home gardener, selecting cuttings from plants he or she wishes to propagate will usually not maintain stock plants but take cuttings when and where available.

Nutritional Status of Cutting

The nutritional balance of the stock plant plays a role in the success or failure of the cuttings taken from it. In particular it is the ratio of carbohydrate to nitrogen content of the stock plants that influences the rootability of the cuttings. Carbohydrates are present in starches – food reserves. Nitrogen is present in proteins – and is in abundance in soft, succulent, young growth.


In general, low nitrogen to carbohydrate ratio is desirable in this respect. The cutting taken from a stock plant with this nutritional balance will have a large reservoir of food resources but not a great deal of succulent growth that decays rapidly. An appropriate manurial programme for stock plants will ensure adequate, but not excessive, nitrogen supplies. It is generally thought that high levels of nitrogen are not conducive to rapid rooting.

Tissues with a high nitrogen content also have low carbohydrate storage capacity. This situation is considered to have a negative impact on rootability.

Ostensibly carbohydrate content can be determined by stem firmness. There is a low carbohydrate content when stems are soft and flexible. Carbohydrate is high when the stem is rigid and snaps effortlessly.

A reduction in nitrogen supply will reduce elongation growth but result in good carbohydrate storage. Soft growing tips are not generally used as carbohydrate storage is poor in such regions of stems.

In poor soils, fertiliser should be applied to permit the growth of healthy growth suitable for cuttings. High nitrogen fertilisers are often not suitable.

Health of Cutting Material

Use only healthy stock – free from viral infections. Unlike seed propagation where diseases of the parent are rarely transferred to the seed to infect the new plant, vegetative propagation may also propagate any diseases that the parent plant may have. In the case of some plants infected with viral diseases, it is possible that the soft growth of shoot tips may not be infected, and may be considered for use as cutting material.

Avoid any material where diseases or pests are obviously present, or where the material is damaged (this may be an entry point for diseases).

The health status of both stock plants and propagules (cuttings) is important at all stages of the propagation process.

Timing

Timing of preparation and insertion of cuttings can be critical with some species. For example lilac can be rooted when new shoots are 6 to 8 cm long and in active growth. This is only feasible for a few weeks. Some other plants will root at any time of year e.g. Ligustrum spp.

It is the physiological and anatomical condition of plant material that is significant and not just the time of year. These can be manipulated by the use of bottom heat and mist or fog systems.

Select cuttings of the appropriate age and at the appropriate time of year. There are specific criteria for each type of cutting:

• For stem cuttings, use juvenile (immature) portions of plant material, which cannot produce flowers or fruit.


Plant group Detail Timing Deciduous species Softwood and semiripe Growing season Deciduous species Hardwood After leaf fall Narrow leaved evergreens Growth flushes, twice per

year Late autumn early winter

Broadleaved evergreens Just after growth flush From spring to autumn Many plants Softwood cuttings Spring or if forced under

glass at any time

• For root cuttings, select roots of adequate maturity that there is sufficient food resources to keep the cutting alive until photosynthesis occurs again. Choose a time of year when this food supply is at its greatest – this is often during the dormant period.

• For leaf cuttings, select those leaves that have only recently fully expanded. These have the most leaf area for photosynthesising. In addition, a fully mature leaf will not undergo any delay associated with completing development that an immature leaf will require.

Figure 45 Leaves Suitable for Leaf Cuttings

Etioliation

Etioliation is the exclusion of light from a growing shoot. In some difficult to root species, etioliated shoots have a greater chance of forming adventitious roots.

Although the mechanism to explain why this occurs is not completely understood, it is believed to be some inhibition of auxin development that is associated with light. In the absence of light, auxin levels may naturally be higher and this results in greater success with rooting of the cuttings. The etioliated tissue also has:

1. Smaller content of starch. 2. Less mechanical strengthening tissues. 3. Thinner cell walls. 4. Less cell wall deposits. 5. Fewer vascular tissues. 6. Larger amount of parenchyma cells. 7. A good supply of undifferentiated tissue.

This African Violet (Saintpaulia cultivar) has some leaves suitable for use as a leaf cutting and many leaves not yet mature enough for use for leaf cuttings.

These leaves are ideal for use as leaf cuttings.

These leaves are too immature for use at this time.


A home gardener is unlikely to keep stock plants within trenches so that cutting material remains below ground, as commercial growers may do. But in the home garden there are alternatives that may be fairly simple to do (for example, tape up stems of the plants where cutting will be taken later, or cover the entire plant in a black plastic cover for a period of time, for example 7 to 10 days, prior to taking cuttings).

Even following insertion of stem cuttings in the rooting compost, they become etiolated to some extent.

Temperature Manipulation of Stock Plant

Sometimes the best cutting material is that taken from a plant that has been initially subjected to a period of cold (for example, temperatures of about 2°C for 2 weeks or so), then a period of warm temperatures (for example, 15°C).

This forcing of young shoots rapidly produces growth that may be the best source of easily rooted cuttings.

However, some planning for this must take place – for example, it may be best to use a containergrown plant as the stock plant since this plant may be easily moved from cool location to warm location.

Treatment of Cutting Material

Now that the fundamentals of stock selection have been described, there are some treatments of the cutting material that will aid speedy rooting.

Cutting material must be handled carefully to ensure the best success in rooting.

• Moisture content When dealing with leafy cuttings (either softwood, greenwood or semiripe cuttings), it is important that moisture content of the cutting remains as high as possible. These cuttings are usually best taken early in the morning before moisture is lost. Cuttings should be kept in cool, moist conditions while they are being collected and should be held in these conditions until they are planted. This helps slow down transpirational losses and helps keep the material turgid.

• Bruising Cuttings should be handled carefully to prevent bruising of the tissue. This is particularly important in handling of cuttings with leaves. Bruising may be the entry point for fungal diseases and start early deterioration of the cutting material.

• Wounding In contrast to the above point, there are times when wounding of the base of a cutting may help stimulate rooting.

For example, Rhododendron and those with older wood at the base benefit from wounding to encourage root formation. The callus produced appears to


stimulate cell division and the production of root primordia. Injured tissue produces ethylene, which is known to promote the formation of adventitious roots. It is also thought that wounded cuttings absorb more water, which helps in the production of roots.

The technique of wounding a cutting by removing a longitudinal sliver of tissue from its base is sufficient to remove a continuous sclerenchyma ring. This may have prevented roots from emerging (as in many species such as olive).

Figure 46 Wounding of Cuttings

• Polarity It is important to remember the polarity of the cuttings. That is, it is essential that the distal portion of the cutting be readily identified from the proximal portion of the cutting.

For stem cuttings, the distal end is the end furthest away from the roots. The proximal end is the end closest to the roots.

For root cuttings, the distal end is the end furthest away from the shoot. The proximal end is the end closest to the shoot.

The translocation and activity of rootpromoting hormones – such as auxin – takes place according to the powers of polarity. This manifests in the production of roots at the proximal end of a stem cutting and shoots being produced at the distal end. Roots and shoots form at different ends in this case.

For many leafy cuttings, and some hardwood cuttings, the orientation of the petioles and buds may easily indicate the “top” of the cutting from the “bottom”. However, for some hardwood cuttings and root cuttings, this is not always obvious. Usually it is best to cut the distal end of the cutting with a sloped cut and the proximal end of the cutting with a straight cut.

By following some standard, it will be easy to ensure that the cuttings are inserted with the top above the bottom when it comes time to insert the cuttings in a compost for rooting.

• Fungicide treatments Protective fungicides used as a dip during cutting preparation can give some protection and result in better survival and improved root quality.

However, organic gardeners usually should not consider these treatments.

Thin section of bark tissue removed.


Although sulphur compounds may be permitted under the organic definitions, they should not be used as a regular, preventative treatment. This leads the organic gardener to using basic hygiene to try to avoid problems with fungal diseases during propagation – ensure only healthy, clean cuttings are used, sterilise all propagation equipment and use a sterilised compost.

Environmental Factors Which Affect Rooting of Cuttings

A number of environmental factors if not adequately controlled can contribute to propagule stress. Alleviation of stress factors is essential for successful propagation. Excessively high or low temperatures, excessive water loss and light levels out of the desired range can limit the rate of root development and can result in death of the propagule. The factors that are most often modified include:

1. Air and soil temperature 2. Relative humidity at the leaf surface 3. Light duration and intensity 4. Nutrition.

Temperature

The most favourable temperature is species dependent and dependent on the type of cutting involved. Species of temperate zones have generally performed well with soil temperatures of 18 to 20°C and air temperatures somewhat cooler than the soil temperatures.

The optimum may be slightly higher for some tropical plants and lower for plants commonly grown in colder climates.

Air temperature in enclosed structures must be controlled. This may be within a greenhouse structure, a cold frame or cloche or a propagation unit within the house or potting shed. Soil temperatures may also be manipulated through the use of soil heating cables.

• Ideally the tops of cuttings should be kept fairly cool, to reduce the opportunity for bud expansion in the case of hardwood cuttings and to reduce transpirational losses for any leafy cuttings.

Reduction of excessive or damaging temperatures can be achieved by appropriate ventilation. This is most needed during the summer but also when high light intensity occurs during winter. There are many ways to ventilate a structure, including passive and active means, but the description of these is beyond the scope of this lesson – this lesson focuses only on the propagation techniques that may be used by home gardeners.

• The use of artificial heat may be advantageous. Early in the season, hardwood cuttings may be encouraged to produce callus tissue faster if placed into a propagation bed that is kept warm through the use of soil warming cables. But the concept is usually “warm bottoms and cool tops”.

Other source of heat, however, may not be necessary and may be detrimental if it encourages transpiration or bud expansion.


Commercial growers use heated structures to speed propagation. Often these growers have purchased cuttings in an advanced state (for example, by importing or purchasing forced leafy cuttings prior to when they are available naturally) or may have forced stock plants into early growth and this dictates a need to maintain the plants in warm temperatures throughout the rooting process.

A home gardener, however, is usually propagating plants from a garden source and, may be using garden beds to propagate plants from cuttings. As a result, the ambient temperatures may be suitable. In these conditions, no artificial manipulation may be possible outside the use of mulches that help warm the soil before planting (for example, black plastic mulches). If a more controlled environment is desired, then using a heated propagation unit is one alternative.

Moisture

The degree of water stress in plants or cuttings is influenced by relative humidity (please refer to the section on transpiration in lesson 2).

In the propagation phase, plant material without roots (cuttings) are particularly vulnerable to water stress. Water loss continues but the lack of root systems prevents water replacement.

The higher the water content of air adjacent to the leaves, the lower the amount of water loss.

Techniques have evolved to address this problem.

• In commercial operations, intermittent mist and fog systems are the primary ways to maintain moisture content on the leaf surface approaching 95 percent relative humidity during the day, when potential transpiration is highest.

• Another technique used by the commercial growers is to keep a layer of polythene film in direct contact with the moistened leaves. This reduces moisture loss from the leaf by transpiration.

• The home gardener may use something as simple as a polythene bag, misted by a hand mister and then sealed to keep the moisture levels around the leaf as high as possible. This is comparable to a humid chamber technique.

This procedure involves confining the crop to a smaller volume of air in which the humidity can be more easily controlled. Disadvantages of this technique include the possible encouragement of disease development by reduced air circulation.


• Plastic propagation units or clear plastic domes may also help keep the moisture levels up around the plant – but these require careful monitoring to ensure that the moisture level does remain high. An inexpensive plastic dome may be created using the bottom of a clear plastic drinks bottle (a 2 litre bottle is a good size to use).

Figure 47 An Inexpensive Home Propagation Unit

It is important to remember that any technique to keep humidity levels up may reduce the amount of light reaching the plant material. This will reduce any photosynthesis that is occurring – the result is slower growth of roots and new shoots. However, desiccated cuttings will not photosynthesise at all, so the loss of some photosynthetic potential is more than offset by the increased turgidity of the plant material.

Some commercial operations use a porous material that is kept moist – a structure called a wet tent is the result. This could allow some air circulation while adding moisture to the environment around the plants during propagation.

The quality of the water applied during propagation is important. The soluble salt levels should be well within the acceptable range. Higher concentration of calcium and/or iron in the water applied through a mist system result in deposits on the leaves. These deposits may not be obvious while the leaves are wet, but a white calcium deposit or a reddish iron deposit is seen when leaves dry.

Light

Both the quality and quantity of light need to be optimum for growth and development of propagules. This is important when rooting leafy cuttings. For example, hardwood cuttings with no need to photosynthesise are not sensitive to day length.

Propagation “unit” for a single African Violet leaf


Some plants are sensitive to day length. During rooting, vegetative growth is desired and an appropriate day length should be provided. For short day plants (like chrysanthemums), cuttings respond to long days (usually between 14 and 16 hours of light per day). For long day plants (like sedum), short days may be best so that vegetative growth is encouraged. For most woody plants, the longer the day length, the greater the opportunity for growth (and root development).

In general, only commercial growers would consider manipulating day length. These growers may extend the day length artificially through the use of lighting equipment or use night break lighting (as described in lesson 2).

An appropriate light intensity is species dependent. Matching the light requirement of any given species may be desirable. Insufficient light intensity will result in etiolated plants with weak stems that are sparsely foliated. Excessive light will stress the plant, resulting in a short, stubby, weakened plant with light green or yellowish foliage.

It is important to maximise photosynthesis during propagation, since the products of photosynthesis are used for growth and development. The light level may have to be a compromise between optimum light for photosynthesis and reduction of water stress and transpiration, depending upon air temperatures and the ventilation capabilities.

In the home garden, maintaining moisture levels in the cuttings is usually a priority and cuttings (within polythene bags or other propagation structures) must be kept out of direct sunlight. Bright but indirect light is often best and some shading may be desirable – for example, beneath the laths of a shade house, or in the shade of a deciduous tree or large shrub.

Fertilisation

When roots of developing cuttings emerge, they can absorb nutrients. However, excessive nutrients in the compost result in high levels of soluble salts that can injure tender roots.

Controlledrelease fertilisers can be used in the propagation medium, but the rate of nutrient release and the period of release must be carefully considered. A controlledrelease fertiliser must be predictable over the range of temperatures and moisture conditions possible in a particular propagation system. Controlledrelease fertilisers may be incorporated in the medium during mixing or applied to the surface after cuttings have been stuck.

Soluble fertilisers applied at moderate rates give more control of nutrient levels in the medium but require more intense management. Soluble fertiliser should not be incorporated in the propagation media.

Organic growers and gardeners may use naturally slowrelease organic fertilisers – for example by incorporating fish, blood and bone meal into the compost before potting on the rooted cutting. A liquid feed of seaweed extract may also provide a boost of nutrients to the rooted cutting.


Establishment of a New Plant

Following rooting, the plant must be weaned from the carefully controlled conditions in the propagation unit or bed. The cutting must be gradually introduced to “natural” conditions. The high humidity levels that may have been maintained around the cutting must be gradually lowered so that the cutting slowly adjusts to ambient humidity levels. If soil warming was used, this also must be removed – although there is usually little need to reduce this slowly.

Over a period of a few days, gradually lower the amount of misting applied, or open the propagation unit (or polythene bag) to permit the entry of lower humidity air into the area around the cuttings. Eventually, the cutting will be able to tolerate normal humidity levels.

Cuttings that have been rooted indoors will also need a gradual adjustment to the light levels outside. This hardeningoff procedure should be gradual, as described for the hardening off of seedlings in the previous section of this lesson.

Some cuttings require some additional time to grow on before they may be planted out into their final location. In a commercial operation, this process is often called “lining out”. The rooted cuttings (or, depending on the method of propagation used, layers) are planted out into a nursery bed in rows (“lines”).

Figure 48 Lining Out of Rooted Cuttings or Layers

A home gardener may also do something similar using a portion of a garden bed set aside to nurse along the tender growth of young plants.


4 VEGETATIVE PROPAGATION TECHNIQUES

By the end of this section, you will be able to describe the production of plants by vegetative techniques in a garden situation:

• Name the types of stem cuttings. • Describe the propagation of plants using a range of

stem cuttings. • Describe the propagation of plants using a range of leaf

cuttings. • Describe the propagation of one plant using root

cuttings. • State the environmental requirements for successful

rooting of each of the types of cuttings defined above (stem cuttings, leaf cuttings, root cuttings).

• Describe the equipment required to propagate plants by cuttings.

• Describe the aftercare required for plants raised by cuttings.

• State the physiological factors to be fulfilled for successful propagation by layering.

• Describe a range of different types of layering. • Describe the aftercare required for plants raised by

layering. • State the conditions which have to be met to ensure

successful propagation by division. • Describe the propagation of plants by division. • Describe the aftercare of plants propagated by division.

Introduction

This section focuses on the specific techniques involved in the vegetative propagation of plants via the following processes:

• cuttings – including different types of stem cuttings, leaf cuttings and root cuttings,

• layering – including simple layering, tip layering, serpentine layering and air layering,

• division.

Budding and grafting techniques will be covered in the next section of this lesson.

Cuttings

The use of cuttings is the most common form of vegetative propagation. Cuttings used in propagation involve stems, leaves or roots. The process is relatively simple and a single mother or stock plant can yield many cuttings. Large numbers of


ornamental plants are propagated in this way. This technique is usually used to vegetatively propagate dicotyledonous plants.

There are a number of types of cuttings: stem cuttings, leaf cuttings including petiole cuttings and bud cuttings, and root cuttings.

In the propagation of plants from cuttings it is essential to produce root growth before shoot growth begins. In most cases the base of the cutting should be warmer then the top. Frequently in the descriptions that follow, it is often stated that bottom heat is desirable (commercial growers use mist benches and electric propagators). Home gardeners, however, may not have the equipment necessary to provide bottom heat and they may still be able to produce plants from cuttings.

Living tissues need:

1. Oxygen 2. Warmth 3. Water and a suitable relative humidity 4. Freedom from poisons 5. Freedom from competition 6. Freedom from excessive osmotic demands. 7. Green, leafy tissues need light and CO2 in the daylight period.

It is important to remember these points when attempting to propagate a plant, particularly when using cuttings.

All cuttings carry the risk of a carryover of pests and diseases. As a result, it is important that the commercial grower avoid cuttings with pests (such as scale insects and stem eelworm) or diseases (like canker). A commercial grower must also ensure that the cutting is from material that is true to type. A home gardener will also try to avoid material with pests and diseases, however there is usually less need to ensure that cuttings are taken from plants that are true to type.

Advantages of Propagation By Cuttings

There are a number of advantages to the home gardener to production of new plants through the use of cuttings. These include:

• Cutting material is frequently available for use (from the gardener’s own plants, from the plants of friends and neighbours) and, given suitable conditions, may be easily transported from one location to another.

• Propagation by cuttings does not require the use of expensive equipment. Although commercial operations use mist propagating units, the home gardener may use easytoconstruct substitutes to keep the humidity levels in the air around the rooting cuttings high.

• A small area may be used to produce a fairly large number of new plants.

Disadvantages of Propagation By Cuttings

Not all plants may be propagated successfully through the use of cuttings. Many monocotyledons are not propagated this way (because the anatomical and physiological basis for regeneration – the lack of vascular cambium in these is the primary barrier to successful propagation by cuttings of monocotyledons).


Some cuttings are so slow to develop adventitious roots that they may perish before these roots are formed. Some plant parts may be capable of producing adventitious roots but cannot form adventitious shoots, thus preventing the creation of a complete plant from the cutting.

Stem Cuttings

The use of stem cuttings is still one of the most common methods of vegetative plant propagation.

All cuttings must survive without roots until these form when the new plant can exist independently. Speed of handling and placing of prepared material into an environment that will enhance root development is fundamental to success. The rooting environment must maintain the cutting until it is selfsupporting.

The appropriate environment will ensure: 1. Appropriate temperatures both above and below cuttings. 2. The maintenance of a suitable relative humidity of the air around the cuttings. 3. Adequate water content of the compost to meet the demands of the developing

propagules.

Taking cuttings is always a challenge because there are variables like the time of year, the quality of the cutting material and the techniques available.

Stem cuttings are the most variable in that they could usually be divided into:

• Softwood (leafy) These include apical meristem cuttings and the surface sterilised larger propagules (for example, single rose eyes) that are now frequently used for roses in “microprop”.

• Greenwood • Semi ripe (also called semihardwood – again leafy) and • Hardwood cuttings (leafy only if evergreen).

The size of the cutting matters. Very small cuttings may need more care than can be provided and too large a cutting may become desiccated due to lack of water. Virtually all the water has to enter through the cut base. If one gains a good root and a good shoot from a smaller cutting, a fine plant can be formed. On the other hand, a cutting just that bit too large may make a scrubby root system lacking vigour and a very poor sparse branch framework of sad shape which may never pick up to make the 100% standard.

The plant is made up of cells. The cells, which divide, are said to be meristematic and are most common in the cambium and at the apical meristems (in the growth buds and shoot tips).

The cut cells at the base of the stem of the cutting have several jobs – one of which is to absorb water. In order to stay alive, the cells need a suitable temperature, water and oxygen, i.e. from the well aerated and drained rooting compost. They must resist organisms of decay like the fungi.

The absorption of water is not quite so easy to get right because the supply of water


needs to be as a thin water film. Standing cuttings in water somehow tends to cause the cells at the bottom to die even though ample water may be absorbed to support the cutting for the time being.

There are more methods than may be described here, but the principles are the same. Attention to detail does matter and not every species roots easily from cuttings. Alternative methods of propagation are usually used for "difficult" species they are usually seed raised, or grafted (or divided or layered).

Figure 49 Longitudinal Section of Nodal Cutting Base

There are no absolutely hard and fast general rules for the time to take cuttings. However it may be said that leafy softwood stem cuttings benefit from the good light of spring and summer. Cuttings of deciduous material rooted in the late summer and autumn may be difficult to overwinter if they shed their leaves. Some evergreen shrubs and tree material will root in the early autumn much better than later in the year (e.g. Garrya), and some deciduous hardwood stem cutting material will root very well at the very end of the winter and just before the spring upward sap flow commences. (Once this starts there is little chance of rooting hardwood stem cuttings.) Many books on plant propagation offer times for rooting species and cultivars.


PLANT TYPE OF CUTTING SEASON/MONTHS FOR PREPARATION

Begonia rex leaf cutting Spring, summer and autumn. Geranium softwood stem August to October. March to

May. Viburnum davidii (evergreen)

softwood semi ripe evergreen hardwood

June, July July, August October to late January.

Buddleja davidii Buddleja (deciduous) Buddleja

softwood stem semi hardwood hardwood

June, July. July, August. October November. December, January, February

Softwood Cuttings

Although softwood cuttings have the greatest potential for forming roots quickly, the nature of the material in the cutting (usually very young, soft tissue) means that the cutting is very susceptible to desiccation. As a result, these cuttings need special care to ensure that it remains viable.

These cuttings are also the most susceptible to bruising (and the resulting fungal infections that may follow this damage).

Softwood cuttings are taken from lateral shoots (of about 7.5 to 12.5 cm long). These cuttings should not be in bud, seed or flower. Avoid taking cuttings from below 45 cm above the soil surface to reduce the number of rain splashed soilborne disease problems.

Cut the cutting off below a node or at a stem junction. This has the advantage of a solid cross section and more naturally present plant hormones.

Internodal cuttings are useful for some plants like Hydrangea. They may root easily enough and from internodal cuttings where the preparation work is a little simpler.

Figure 50 Internodal cutting of Hydrangea macrophylla

100 mm

The cut is made in the internode – between the nodes.

node


Figure 51 Softwood Stem Cuttings (e.g. Weigela Bristol Ruby)

Cut below a node. This “flat cut” for examination purposes is best cut square as shown. But in practice most cut through at a slant cutting “with the grain” is easier and quicker.

These have leaves and are made from the first flush of growth in spring. These cuttings are taken before lignification, which can include young soft growing shoots during periods of continuous growth or a flush of growth at other times.

New spring growth of Forsythia, Magnolia, Weigelia and Spiraea and even some maples root particularly well under the right circumstances.

Their stems are normally very soft because they have grown extremely rapidly; and they require sophisticated environmental controls to minimise water loss and so ensure their survival until they become established. Whenever possible, try to keep the temperature at the basal end warm (perhaps between 23 and 27 o C) to encourage root formation and the temperature around the foliage cooler to reduce transpiration.

Sometimes the term herbaceous cutting is reserved for leafy cuttings of herbaceous plants which are broadly similar to softwood stem cuttings and need the same degree of care and environmental control.

Time of collection: • Cuttings should not be taken by calendar time alone, but at a particular

growth stage of a plant usually during midApril to July period. • Collection is best undertaken early in the morning, before transpiration has

reached its peak, thus helping to prevent any loss of turgidity. • Collection of material with high nitrogen to carbohydrate ratio, high water

content and low dry matter. • Some species must be taken at a particular stage of growth, which may last

for only a week or two e.g. Syringa.

At least two good leaves should be included on each cutting. Lower leaves are removed.

To reduce the number of cells cut (and the resulting water loss), cut straight across the stem and not on an angle.


Selection of material: • The best propagation material is obtained from growth exposed to full light but

is not excessively vigorous. • All shoots used must be from healthy stock; in many cases stock plants are

specially grown for the production of young vigorous growths. • Hard pruning of stock plants results in lateral side growth, which often yields

good material.

Preparation and size of cutting: • Remove all flower buds and depending on species the soft tip. • The lower leaves are normally removed although sometimes are not. • If these are not removed they can rot off and especially in species like

Cotinus coggygria may lead to Botrytis infections. • Retaining leaves does however increase the photosynthetic area of the

cutting and can reduce rooting time. But retained leaves also mean increased transpirational losses. A home gardener may reduce the number of leaves (or reduce their leaf size) to reduce transpiration even if this means an increase in the length of time it takes for roots to form. Commercial growers, with specialised misting or fogging systems do not need to make this compromise.

• Shoots selected should have a terminal bud and at least two nodes. • Cuttings may be nodal or internodal, depending on species and the size

ranges from 5 12 cm long.

Preplanting treatment: • Softwood cuttings respond very well to hormone treatments. Just the lowest

portion of the cutting should be inserted into the hormone (or organic substitute) – extra hormone should be knocked off.

• Apart from hormone treatment, no special treatment is required. • Handle cuttings quickly after taking and ensure they are kept turgid.

Insertion and care during rooting: • A suitable compost may be any of:

o Equal parts peat and grit or sand. o Equal parts peat and perlite. o Equal parts peat and terragreen ∗

o Equal parts grit and terragreen. The compost must have very low soluble salt levels. It must hold moisture but remain well aerated. It must have a texture which is comfortable for roots and root hairs.

• A dibber should be used to make a small hole in the cutting compost. Then the cutting should be inserted, the compost firmed against the cutting. Once all cuttings have been inserted, the compost should be watered and the container labelled.

• Ideally, a relative humidity of 100% should be provided around the leaves to reduce transpiration losses while the cutting is not able to replenish the lost moisture through roots. In a commercial setting, softwood cuttings are usually inserted under mist. A home gardener may use a mist system (there are ones designed especially for small greenhouses) or may just use other

∗ Terragreen is a gritty, granular, claylike material.


methods to increase the relative humidity in the air surrounding the leaves. However, some plants (for example woolly plants) do not like mist. One of the simplest methods is to place the pot with the cuttings within a polythene bag. This sealed bag, placed out of direct light, will provide a suitable environment for rooting a few cuttings. Another involves the use of bell jars. The cuttings must remain turgid to keep photosynthesising – the more food produced, the faster the root development.

• The cuttings should be in setting with the level of illumination equivalent to that of a bright, cloudy day. Some open opaque shade helps. The cuttings must never be exposed to bright, direct sunlight while they are still developing roots. Too much light may cause excessive tension within the leaves, resulting in closing stomata. The goal is to keep the cutting photosynthesising steadily. Closed stomata reduce photosynthesis, as do excessively dark conditions. Some commercial growing operations also use night break lighting to ensure that the plants are exposed to long days (or short nights).

• A home gardener may consider some soil warming, if the cuttings are being rooted inside a greenhouse. Ideally temperatures of between 23 and 25°C will help speed rooting and many commercial propagators do provide some soil warming to speed rooting. This helps the cells at the base of the cutting to divide and heal the wound. Later it will assist in cell division at the new root tips and stimulate water and soluble salt absorption by the root hairs. However, ambient soil temperatures from during the late spring and summer months may be suitable for the home gardener.

• Rooting can be expected in 2 to 6 weeks depending on species.

Figure 52 A Rooted Greenwood Cutting of Daphne cneorum (Garland flower)

Many woody shrubs and trees may be propagated using this technique – both deciduous and broadleaf evergreen. Some species commonly propagated using softwood cuttings include Syringa, Cotinus, Magnolia, Clematis, Hamamelis, Azalea and many herbaceous plants.

After cuttings have formed roots, the cuttings have to be potted up or lined out into a nursery bed. Those cuttings rooted under mist will require some period of adjustment to


ensure they are weaned off the very high moisture levels. In addition, some species need to experience a period of drying off from the very wet state in order that development of root hairs occurs.

Often a loamless compost/bark mix (with ample feed for immediate growth and sustained nutritional resources) is used for potting up. The ideal compost is stable, well aerated, holds lots of water and nutrients, and is free from pathogens. John Innes mixes were often short on the capacity for aeration and moisture holding if compared with the peat and forest bark and controlled release ∗ fertiliser mixes and FTE (the fritted trace elements which provide the micro nutrients for the life of the compost).

Greenwood Cuttings

Greenwood is the term used to describe that transition from soft wood (fresh growth) and the more mature wood of semiripe wood. Greenwood is that which has started to firm up – secondary thickening has commenced. Usually there is a distinct colour change occurring, both in the colour of the stem and also in the colour of the leaves.

This type of cutting often requires as much attention as the softwood cutting. These cuttings are also prone to excessive moisture loss by transpiration.

A wide range of trees and shrubs are propagated by greenwood cuttings. For example, gooseberries are frequently propagated this way. However, those plants that are very difficult to propagate should use softwood cuttings rather than greenwood cuttings. Greenwood cuttings require more time for roots to successfully develop.

Greenwood cuttings are taken when the spring growth of the plant has started to slow – often near the beginning of June. Cuttings must be protected from desiccation – they should be taken in the early morning, placed in either a moistened polythene bag, or in a container of cool water. Discard lower leaves. Dip the base of the cutting in a rooting hormone (usually the grade of hormone identified for “softwood” strength). Make a hole in the surface of some welldrained, moisture retaining compost, place the cutting in the hole, firm the compost, label and water in. The container should be placed within a polythene bag or under mist to ensure that excessive moisture loss does not occur. Some light should be provided because the cutting also needs to photosynthesise. These cuttings do not have sufficient stored food to fuel root growth without photosynthesising.

Once roots have formed, gradually wean the cutting from the high humidity environment it has enjoyed. Repot or plant out into a nursery bed to grow on.

SemiRipe Wood Cuttings

Semiripe wood (or semihardwood) is that which occurs later in the growing season. As the summer progresses, lignification intensifies and, as a result, these cuttings are both thicker and firmer than greenwood cuttings. Although deciduous plants are propagated as semiripe wood cuttings, many broadleaf evergreens and conifers are

∗ Controlled release fertilisers identified include Ficote and Osmocote products. These are not suitable for use by an organic gardener but there are slow release organic substitutes. These are covered in more detail within lesson 7.


propagated at this stage.

Semiripe wood has an advantage over both softwood and greenwood in that the cutting has been able to store some food resources. These cuttings are capable of producing roots without the urgent need to photosynthesise.

There are a number of different types of cuttings classified as semiripe wood cuttings. These include: leaf bud cuttings, nodal tip cuttings, nodal stem sections and heel cuttings.

Figure 53 Leaf Bud Cutting (Ficus elastica)

These need treatment in virtually the same way as greenwood cuttings. They root more slowly and more reliably perhaps for the amateur with less than ideal facilities. The snag with deciduous material in particular is that if the plant fails to make adequate food storage within itself before winter and leaf fall, it may fail to grow out in the spring. This is the reason why the majority of material propagated by this method is evergreen or semievergreen.

The main season for such cuttings is in July and August. The simple tented system below provides for all the principles and works well for the common species.

These are made in late summer from stem growth that has slowed and hardened but is still actively growing. Although these leafy stems are subject to water loss, they can survive under less rigorous environmental controls than softwood cuttings.

These cuttings may be collected any time during the growing season when shoots are at the correct stage of development – that is, the wood is no longer “greenwood”. Normal collection time is July to September, when there is a slowing down of growth, buds set, stem colour change, high carbohydrate to nitrogen ratio, a lower water content than softwood cuttings, and higher dry matter. Cuttings should be selected from plants of moderate vigour and that are free from insect (e.g. aphids) and disease attack.

A semiripe cutting is one, which has not yet reached seasonal maturity, but is beyond the stage where it could be used as a softwood cutting. The base of the cutting should be lignifying (becoming woody) whereas the tip should still be soft.

The preparation and size of cutting used: • Cuttings may be taken, internodal, nodal (especially for hollow stems), or with a

heel. • Size relates to species but range from 7 12 cm long. • Lower leaves should be removed.

high relative humidity

O2 provided by open rooting media

T o C to suit the species

low salt levels in the soil solution


• Heel cuttings should have excess heel trimmed off. • Mallet cuttings are advantaged, as all of the meristematic tissue is intact.

However as there will be two cut surfaces there is an argument that there is a larger surface area to heal.

Preplanting treatments include: • Handle immediately after preparation. • May be wounded and / or treated with hormones.

Cutting insertion and aftercare include: • Rooting is obtained under glass. • Depending on the size of the cutting, insert 5 15 cm apart, and 10 12 cm

between rows. • Good light, high humidity and bottom heat are required for satisfactory results. • Bottom heat, if used, should be around 21° C. • Depending on the species being propagated, the compost may vary from pure

sand to peat / sand (50 / 50 ), or perlite / sand (25 / 75 ). • May be rooted in cold frames.

A suitable setup for the home gardener may be: North side of bush in the shade

Water the tray once thoroughly and drain before putting into the poly wrap.

Loosely wrapped clear polythene bag.

60mm deep tray well filled with cuttings.

Good garden earth no fertilisers and no obvious slugs, snails, woodlice or millipedes.

Figure 54 A System for the Amateur

Alternatively, trays of cuttings may be placed in a cold frame, cloche or cold greenhouse as long as conditions are moderately shaded.

The species commonly propagated using this technique include Ribes, Camellia, Cotoneaster, Escallonia, Deutzia, Philadelphus, Vinca, Clematis, Ceanothus and Berberis.

Hardwood Cuttings

Hardwood cuttings are frequently made from leafless dormant stems of deciduous plants. They require minimal environmental control for survival. Evergreen


hardwood cuttings are also taken but are treated differently.

For the commercial grower, propagation by hardwood cuttings is one of the cheapest methods of vegetative propagation. A home gardener may also take advantage of the fact that little ancillary equipment is required for the simpler methods. Some hardwood cuttings, however, are best made within the protection of an outdoor frame or under mist.

Plant material used for hardwood cutting preparation is taken from mature, ripened wood of the most recent growing season's growth. Depending on species hardwood cuttings are prepared and inserted between November and February. The most important aspect of a hardwood cutting is that it has an adequate store of starch that will be used to fuel the growth of adventitious roots and the growth of a shoot. Once the shoot starts to photosynthesise, the new plant may start to manufacture new food.

Sometimes the bottom of the cutting is “wounded”. As a technique, wounding is definitely an advantage for those with good facilities because it may "let the roots out" more quickly. Apart from roots, which may arise at the base of the cut and from the callus, many roots could arise from the central vascular cylinder within the bottom few inches of the cutting. The problem for such root primordia may be the physical constraint of the cortex. A thin slice into the bark and down to the xylem may permit the roots to come out more quickly and reliably. However, care must be taken to ensure that these wounds are not additional sites for infection entry.

Deciduous Hardwoods

These cuttings have their store of starch. They are best taken from juvenile wood as would be produced by a hedge. Indeed many major propagators keep their stock plants in hedge forms because the system tends to produce large numbers of fairly uniform cuttings. These are low in nitrogen and high in carbon as against the very dominant shoots perhaps at the top of a young plant which may have a higher nitrogen to carbon ratio and which root less readily.

Figure 55 Stock Plants Used to Supply Cutting Material

The season for rooting ends when the sap begins to rise in the early spring. Traditionally November is a very good time. For some species it may be better in October or even in early March just before the breaking of spring. It pays to keep a record of the treatments so that improvements may be aimed for as each season and crop of results is likely to vary and even tantalisingly good results may be difficult to

discard cutting material below 450mm due to rain splashed spores of diseases from the soil

avoid ultra vigorous shoots


repeat.

The ideal hardwood cutting material – “Fairly thin and hungry to grow”.

The steps involved in propagating a plant through the use of hardwood cuttings are:

1. Take cuttings of suitable plant material while the plant is dormant – well before bud break occurs.

2. Place these cuttings in a suitable location to permit wound healing and callus formation.

Two different activities must occur – the formation of callus tissue that heals the wound (the ends of the cutting are effectively wounds) and the creation of adventitious roots. Both of these activities usually occur best when the base of the cutting is kept warm. Even temperatures of 10 o C are much more stimulating than the outdoor winter temperatures.

Cuttings taken in midNovember may not callus before midMarch a long period for an open wound which provides an opportunity for pathogens (like stem rotting fungi) to enter. Often reduced rooting percentages also occur when a cutting has been slow to develop callus to seal the wound.

Figure 56 The Traditional Deciduous Hardwood Stem Cuttings of Ribus nigrum, Black Currant

To encourage both callus and root formation, cuttings may be placed in a bed

Open sunny site, well drained soil. Rows spaced 1 m apart. Cuttings spaced 300 mm within row. Season – October to March.

soil level

depth of insertion approximately 200 mm.

flat cut below a node

base of rooted cutting

roots may start

The cuttings take 2 to 3 weeks to callus under ideal conditions. The cambium tissue produces the woundhealing callus tissue cambium

callus


with bottom heat. Commercial growers often use something called a Garner Bin – more about this later in this section. A home grower may place the cuttings into a propagation unit with bottom heat.

It is essential that the top portion of the cutting not receive heat. Bud development and bud break must not occur before the cutting has formed an adequate root system.

3. Once the cutting has developed an adequate root system, the top growth may be encouraged.

Once the cuttings are callused, they can be put into "waiting" beds or frames to await the spring when the nursery site may be prepared to receive them. Callused cuttings are quite fragile, and so for most soils it would not be ideal to push them into the rotovated earth (as is quite reasonable for a standard cutting) and then firmed. It is better to insert the cutting into a prepared hole and then firm it. A hazel stick "dibber" might do just fine. (Commercially fine grooves are cut in the soil with discs.)

If this occurs before the root system forms, the stress of supporting leafy growth (and the increased transpiration associated with this) may cause the cutting to die. A root system is needed to provide the moisture requirements of the growing shoot.

A home gardener may not differentiate between the second and third step – and place cuttings directly into a nursery bed in the garden. Although this delays the formation of callus and roots (through cold soil temperatures), cuttings will still root and develop shoots. The nursery bed should be in a sheltered location, with welldrained but moist soil. Root development requires the same conditions as other plant growth – a balance of oxygen and moisture.

A number of ornamentals (both trees and shrubs) may be raised in this way. Many dogwoods (Cornus spp.), willows (Salix spp.), grape vines (Vitis spp.), and Forsythia, just to name a few.

The pattern of taking the cutting follows the practices before of cutting below a node or at the junction with older wood.

Traditionally hardwood cuttings are inserted in a shallow trench, one side being vertical with the bottom lined with sand if the soil is heavy. Recent experiments confirm that if cuttings are pushed through black polythene laid flat and secured, the results are much improved. The warmer conditions underneath encourage callus formation and rooting, no weed competition can occur and more moisture retention, but with less chance of waterlogging.

One method suited to propagation by a home gardener is to root hardwood cuttings in a roll. A strip of black polythene (about 5 cm wider than the longest cutting, and a metre or 2 in length) may be used as the propagating environment. Place the polythene flat on a surface, and cover it with about 1 cm of a mixture of peat and fine bark. On top of this mixture, place the individual cuttings – each about 3 cm apart – with the base of each cutting about a third of the way up the polythene strip (this will leave the top portions of the cuttings sitting above the top edge of the polythene strip). Make sure you label it and tie it securely with jute or raffia. Water well and place these bundles into a sheltered location in the garden or a cold frame. In spring, check to see if they have


rooted, and line them out into a nursery bed to develop fully.

Some plants propagated by hardwood cuttings tend to produce suckers. To limit the production of suckers, the lower buds are removed from the hardwood cutting before being placed to form roots (leaving only the top two or three buds on each cutting). This is often performed for gooseberry and red currants. The wounds created from cutting out the lower buds are often treated with a fungicide to prevent disease organisms from penetrating through these sites. This procedure is called growing on a leg.

Figure 57 Cutting for a Bush Grown on a "Leg"

Other types of hardwood cuttings include: • Mallet cuttings

Figure 58 A Mallet Cutting of Berberis stenophylla

A mallet cutting really does work better for Berberis.

• Vine eye cutting

Figure 59 Vine Eye Cutting Vine eye cuttings are traditionally used to propagate vines, however they

older wood

Top buds retained – 4 in this sample

Lower buds removed to prevent sucker growth later

Sometimes the cuttings are cut in the centre lengthwise before placing on the rooting compost


may also work for any woody plant that produces a solid stem. The length of stem is cut so that only one bud occurs in the centre of the cutting. Then this cutting is placed into the compost, so that half of the wood is buried and the bud remains above the compost level. Sometimes the stem portion of the vine eye cutting is sliced in half.

• Willow sets A set is the word used to describe a cutting of length between 1½ to 2 metres in length. This wood is from the last season’s growth (the youngest wood on the tree). The technique is used to propagate plants to provide a windbreak, Because willow produce such easy to root cuttings, these sets are placed where they are to grow on, and are staked, just like a young tree would be.

Evergreen Hardwoods

A commercial nursery may root small hardwood cuttings of evergreen shrubs under double polythene but without heat.

Figure 60 Professional Environment for Rooting Evergreen Hardwood Cuttings

In a commercial operation, large numbers of cuttings need to be rooted and grown on quickly. However, in a home garden, only a few cuttings may be started and these may be allowed to root more slowly – in a sheltered location in the garden or in a cold frame. However, any additional protection that will permit the cutting to receive additional humidity will assist in the speed of rooting. A small polythene tent (either within a greenhouse or under a tunnel cloche) will help keep these humidity levels up. The reason why evergreen cuttings require addition care to humidity levels is that the leaves continue to lose moisture through transpiration (deciduous hardwood cuttings do not have these moisture losses).

Weed control by hand is desirable, weeds depress crop growth and quality enormously.

Evergreen cuttings may be collected between late autumn and late winter – the exact time varies from species to species. Cuttings should be taken when plants are "completely dormant". Each cutting should be between 5 and 25 cm long. The lower leaves are usually removed and a hormone treatment or basal wounding is often carried out.

Mature terminal shoots of previous year's growth are normally selected although in some cases (for example Taxus and Juniperus) older and heavier wood may be used. In some species side growths give better results than tip growths. In

equal parts peat/grit /loam

floating polythene cover


Juniperus species, many of the juvenile foliage forms root more readily than the adult foliage types.

Usually cuttings are inserted between 5 and 15 cm apart, with 10 to 15 cm between rows.

Species that are commonly propagated by hardwood cuttings include the following conifers: Thuja, Chamaecyparis, Juniperus, Taxus, Picea, Tsuga, Pinus, Cryptomeria, Cupressus and x Cuprocyparis.

Although broadleaf evergreens are less likely to be propagated by hardwood cuttings, many may be done using this method. Some examples include Prunus lusitanica and Olearia macrodonta. In the case of broadleaf evergreen hardwood cuttings, each cutting is usually 50 cm long and placed into pots for rooting and growing on. Because of the increased moisture losses through transpiration occurring at the large leaves, these are often decreased in size.

Figure 61 Broadleaf Evergreen Hardwood Cutting

Leaf Cuttings

Some plants may be propagated from single leaves. Although the leaves of a number of different plants are capable of rooting (for example the leaves of Clematis may produce adventitious roots), not all are also capable of producing adventitious shoots. The new plant will need both roots and shoots to be a fully functioning new plant.

A surprising number of plants have this ability. A number of monocotyledonous plants will reproduce from leaf cuttings. Some dicotyledonous plant families in particular have the ability to be reproduced from leaves – Begoniaceae (Begonias), Crassulaceae (a family of succulent plans) and Gesneriaceae (the family that includes the African Violet, Saintpaulia spp., and Cape Primrose, Streptocarpus spp.).

Leaf cuttings consist of:

• Leaf petiole cuttings

Leaf petiole cuttings are those where both the leaf blade and the leaf petiole are removed from the plant. The petiole is inserted into a suitable rooting medium.

The lines mark the location where the leaf reduction cuts may be made.


After adventitious roots develop, plantlets form from the tissue of the petiole.

Perhaps the most common example of plants propagated this way is the African Violet (Saintpaulia spp.).

Figure 62 African Violet Leaf Petiole Cutting

• Leaf squares

One technique for propagation of plants with large leaves is to cut the leaf into postagestamp sized pieces. This technique is used to propagate Begonia rex. Healthy leaves are removed from the parent plant and the petiole is removed. Then, this leaf is cut into pieces about 2.5 cm square using a very sharp knife. It is important that each leaf piece have a section of a main vein running somewhere through it (these are the sites where the new plantlets form) and that the leaf section not have any bruising or damage on any part (these will be sites of decay).

There are two techniques used for rooting these cuttings. One is to put each of these squares flat on the surface of the cutting compost (pinning each main vein portion of the square to the compost). The alternative is to place these leaf squares into the compost vertically, just as the sections are inserted for lateral vein leaf cuttings (see below). This option requires a little more care because it is important that the section of the leaf closest to the petiole (and parent plant) is inserted into the soil.

• Lateral vein leaf cuttings

A number of plants with long, narrow leaves may be propagated by lateral vein leaf cuttings. Many monocotyledons may be propagated this way. Streptocarpus (Cape Primrose) are also propagated using this technique. Once again, healthy, mature leaves are removed from the parent plant and cut into pieces across the midrib. These pieces are then placed vertically into a suitable cutting compost ensuring that the proximal end (the end closest to the parent plant) is inserted into the compost leaving the distal end (the end closest to the leaf tip) out of the compost. Some monocotyledonous plants are not sensitive to the polarity of the leaf cutting being maintained.

• Midrib leaf cuttings

Some plants develop new plants at the point where their leaf veins intersected with the midrib. An example is Streptocarpus. A healthy, fullyexpanded leaf is removed from the parent plant, it is placed upside down on a clean surface (often a clean piece of glass is used) and then the midrib is carefully cut away.

Plantlet will arise from the base of the petiole


The two sides of the leaf may be potted up in a suitable rooting medium (for example, moistened vermiculite or a cutting compost).

Figure 63 Cuttings That May be Taken From a Streptocarpus Leaf

• Leaf slashing

Leaf slashing is often used to propagate some large, fleshy leaved plants like Begonia rex. A healthy, mature leaf is removed from the parent plant. First, the petiole is removed carefully where it connects with the lamina (blade). Then, the lamina is placed upside down on a clean surface and, using a sharp knife, cuts are made across the large veins (about 1 cm long). Cuts may be made every 3 cm or so. This cut leaf is placed on a suitable compost with the cut side facing up (that is, the top side against the compost). It is secured to the compost – often by using small wire loops over each vein cutting. After a period of time, small plantlets will form at each cut location.

• Foliar embryos

Some plants produce plantlets at different places on the leaf. The Thousand Mothers plant (Tolmiea menziesii) produces plantlets where the leaf petiole joins with the lamina. Some Kalanchoe species produce plantlets at the sites of indentations in the edge of the leaf.

• Bulb scaling

Leaf scales are also considered a leaf cutting. Many bulbs may be propagated through the use of bulb scales. The scales of the lily bulb are particularly obvious and may be removed carefully from a bulb (this is made simpler by using a sharp knife to make a small cut into the basal plate). At this point, there are two options that may be taken:

o Each of these healthy scales may be potted in moist sand or vermiculite – inserting the base of the scale into the mixture leaving only the tip of each scale showing.

o Placing the scales into a polythene bag containing moistened vermiculite, or peat.

The lines illustrate the cuts that may be made to produce midrib leaf cuttings.

These lines illustrate the cuts required to make transverse cuttings.

New plants will form along the basal edges.


Usually about 4 to 8 weeks later, small bulblets will appear at the base of each scale. Each bulblet may be grown on to, eventually, form a flowering bulb.

Figure 64 Scaling Lily Bulbs

Root Cuttings

The theory behind using root cuttings is that a plant should be able to produce adventitious shoots from a root cutting just as easily as a cutting from a shoot may produce adventitious roots.

Unfortunately, few plants are easily propagated through the use of root cuttings. Those woody plants that have a tendency to produce suckers may be propagated by root cuttings – for example Bottlebrush Buckeye (Aesculus parviflora) and Lilac (Syringa spp.). Some perennials and alpines that produce somewhat fleshy roots may also be propagated by cuttings – for example, Primula denticulata, oriental poppy (Papaver orientalis) and garden phlox (Phlox paniculata) may be successfully grown from root cuttings.

This form of propagation is used for species and cultivars difficult to root in other ways. For example, Phlox paniculata cultivars (but not the variegated leaf forms like Phlox 'Norah Leigh') may be produced through root cuttings while other methods of propagation are difficult.

The main disadvantage is that the 'donor' plant has to be disturbed.

The technique cannot be used to propagate plants originating as chimeras. Plants, such as the variegated Aralia and Pelargonium, will revert to the normal green (un variegated) form following growth of adventitious shoots.

One advantage of this mode of propagation is that some pest problems may not be passed on to the new plants. For example, Phlox root cuttings are free from the stem eelworm.

It is important that the root cutting contain as much food as possible to fuel the developing adventitious root and shoot. Unlike leafy cuttings, the root is unable to manufacture food through photosynthesis until the shoot has been formed – and this new shoot is sometimes formed after the creation of adventitious roots. As a result, the best time to take root cuttings is when the plant is dormant. At this time, the carbohydrate stored within the root is the highest level.

The general advice is to select root cuttings that are about as thick as a pencil (about ¾ cm) and between 5 and 10 cm long. However, smaller roots may be successfully propagated (and in some cases, the plant does not possess roots as thick as a pencil to select). However, keeping in mind the idea of food storage, if the roots are thin, then the cutting should be longer.

bulblets forming at the base of a scale


The basic steps involved in propagation by root cuttings are:

1. dig the parent plant while it is dormant

For many plants, this is between midautumn and late winter, before the start of new growth for the new season. However, for the oriental poppy, this is usually midsummer.

2. carefully wash the soil off the roots

3. select some of the strongestlooking roots, sever them from the parent by cutting as close to the crown of the plant as possible.

Do not take more than about one third of the roots from the parent plant, if the parent plant is to be replanted and grown again.

Roots may be placed vertically in the compost or horizontally on the surface of the compost.

Usually thicker roots are placed vertically so it is important remember which end of the root came from the portion nearest the plant crown (the proximal end) and that portion that was most distant from the crown (the distal end). This maintains the polarity of the cutting. Usually the distal end is cut with a sloping cut and the proximal end is cut with a flat cut.

Thin roots will be placed flat on the compost surface, so it is not necessary to make distinctive cuts to identify the ends.

Cuttings may be treated with a fungicide, but they are not treated with rooting hormones.

4. Place the root cuttings in a location for to develop.

There are two choices for starting root cuttings.

Thick roots may be grown outdoors or in a welldrained compost in a greenhouse.

o Outdoor propagation usually involves the bundling of these thick root pieces. These bundles are kept in damp sand or peat moss at about 4°C for about 2 to 3 weeks while the callus develops. Then the roots are inserted into a suitable nursery bed or pots (with welldrained, moist soil) so that the proximal end is just at or just below the surface of the soil.


Figure 65 Root Cutting

o Indoor or under glass propagation does not involve a separate period for callus formation. The cuttings are inserted immediately into pots, pans or trays (filled with an open, freely draining compost that has already been watered). Again, the roots are inserted with the proximal end at or just below the surface of the compost. A dibber is used to make holes into the compost as deep as the root cutting is long. Once the roots are placed into the compost, and the container is labelled and the surface of the compost is covered with a 1 cm layer of grit or coarse sand. These pots should be placed in a cold frame or propagator. The compost should only be watered to keep it from drying out – the grit mulch will help retain moisture in the compost.

Thin roots are usually only started under glass. The roots are placed on the surface of a moistened, freelydraining compost and are then covered with about 5 mm of compost. A top dressing of grit or sand is then added onto the compost and the labelled containers are placed into a propagator.

In all cases, when new top growth occurs (this may take place a year later), the cuttings should be carefully lifted to confirm if adventitious roots have also developed. When root growth has occurred, these are ready to pot on to larger containers. These rooted cuttings must be grown on, with careful management of temperature extremes, until they are large enough to be planted out.

? How would you propagate perennial Phlox to obtain a stock free from eelworm (nematodes)?


Equipment for Propagation by Cuttings

Heated Propagation Units

Professional propagators have extensive systems to support the cutting during the rooting process. Within a glasshouse environment, special heated benches provide

sloping cut at distal end

flat cut at the top

cover with 1cm of sand or grit


bottom heat.

Figure 66 A Heated Bench for Propagation of Cuttings

Usually these heated benches use the heat produced by running hot water or steam through pipes that lie beneath the bench. Home gardeners may create a smaller version of these through the use of electrically heated propagators or soil heating cables.

Figure 67 Heated Propagation Unit

Cold frames may be used to root cuttings that are too soft or weak for the outdoor methods. Each cutting is carefully inserted at 5 to 8 cm centres in a frame with light soil or made up compost used as a rooting medium with 1cm of sand covering.

polythene film cover

mobile benching for economy of glasshouse space

pathway pathway

flats or rooting trays

Polythene film cover touching foliage

Frame support

Heating cables are looped within a bed of sand – the cable loops are carefully arranged to ensure they do not touch other loops.

Above the cables is another bed of sand – with a thermometer in it to ensure the temperature is suitable.


Garner Bins are used to speed the callus formation and root development on hardwood cuttings in commercial propagation operations. In essence a soil warmed compost where the base of the cuttings are kept at around 20 o C.

Figure 68 A Modified Garner Bin

There is much to be said for bundling the cuttings and inserting them in a protected site like a frame surrounded by straw bales. The compost they are stood in should be of such a quality that it is never sticky wet a very open gritty earth and some granulated peat might work well.

Mist

To maintain relative humidity around leafy cuttings, commercial propagators use automated misting systems or fogging systems. Mist systems keep the leaf surface wet (thereby reducing transpiration losses while permitting photosynthesis to occur). After rooting has occurred, the cuttings are removed from the mist environment. Most plants suffer during the move, as under conditions of mist few root hairs are produced, hence a weaning period is necessary. At least one firm produces a "weaner" which automatically reduces the amount of water falling on the rooted plants, thus allowing the change in regime to be carried out in controlled stages. If a "weaner" is not used and the plants are struck in the bed itself, the change can be to some extent offset by placing the cuttings, when potted off, into a closed frame for a few days, after which they can be placed on the open benches.

A dedicated home gardener may be able to purchase or construct a small mist unit to be used in a home glasshouse.

Some passive systems may be used to help maintain relative humidity around leafy cuttings. These systems work by confining a volume of air around the cutting – once this air becomes moist, it remains moist for a long period of time. Some choices that may be used by a home gardener include plastic propagation units, cloches, polythene film, or even plastic bags supported over the cutting and plastic bottles (as described in the previous section).

Compost of peat and grit, free from lime

rainproof cover

Cuttings best singly or conveniently in small bundles

Soil warming cables Thermostat

Tops of the cuttings cool at the ambient outdoor temperature

Base of cuttings at 20°C


Rooting Media

Experiments have been carried out at various centres and by individual growers, and there are different opinions as to what is the best. Whatever is used, it must be a free draining material or the bed will become soaked and remain so. A suitable medium seems to consist of four parts coarse perlite or sand to one part compost. Some compost seems necessary, partly perhaps to create a more acid rooting medium, e.g. for such plants as Rhododendrons and Ericas.

Whilst it is the common practice to root the cuttings into the bed, some commercial growers are now using the bed as a plunging medium and are striking the cuttings directly into pots or boxes. This eliminates the problem of having to move them when the cuttings have rooted.

Aftercare For Plants Produced By Cuttings

Once rooting has occurred and the plant has both a fully functioning root and shoot, the new plant must be prepared for survival outside of the propagation environment. This process should occur gradually so that the new plant is not overly stressed at any one time. The amount of care that a cutting requires depends on the type of cutting, the time of year and the environment under which this plant was propagated.

Those cuttings that were propagated under mist (or other protected environments with high humidity levels) need to be gradually acclimated to lower humidity levels (the conditions that they will grow under in the future). This is best done over a 2 to 3 week period.

If bottom heat was used, it is often turned off first. Then the humidity level is gradually lowered to natural levels – plants grown within plastic domes or polythene bags must be gradually exposed to the air outside their protective chambers. The length of time that the cuttings are exposed to “normal” conditions should become longer each day. Once weaned of heat and humidity, they should be acclimated to higher light levels.

The cuttings should be monitored to ensure that excessive shoot growth does not occur – this may be too much for the new root system to support. Usually this is done by a reduction in watering. Watering is reduced gradually so that the root system begins to tolerate slightly drier compost conditions – water is not withheld to the point of wilting, but the frequency of watering is slowly reduced.

New plants may need additional protection from winter temperatures. For those more tender plants, winter in a heated glasshouse may be needed. For less tender new plants, winter in a protected area of the garden or in a cold frame may be adequate.

Layering

Layering of plants in reality is the preparation of a plant for subsequent division. Only after adventitious root formation is the layer detached and planted as a separated plant. The advantage to layering is that the stem that will eventually become an independent plant remains attached to the parent plant (receiving water, nutrition and hormones from the parent plant) during the formation of adventitious roots.


In some species, layering occurs naturally. Climbing plants often exhibit this ability (for example, Ivy, Hedera helix, often develops roots when permitted to trail across the ground). Strawberry plants (Fragaria sp.) naturally produce plantlets on runners and these often root where they touch the soil surface.

Layering is often used in species that may be particularly difficult to root from cuttings. The home gardener may use layering as a fairly certain method for producing a small number of plants. Commercial growers, however, do not routinely use this method because it is not the most efficient use of plant material or space.

In a commercial environment, layering beds are established to grow stock plants. Because these beds are frequently used for many years, utmost hygiene has to be practiced to prevent the spreading of pests and diseases, especially nematodes and viruses.

The formation of roots is stimulated by treatments of the stem that interrupt the downward movement of carbohydrate, auxin and other rooting factors from leaves. These treatments stimulate root formation in the area of the treatment. These materials accumulate in the region of the stem to be layered and encourage roots to develop.

Rooting requires sufficient moisture, good aeration and reasonable temperature, which are provided by a light sandy soil. Irrigate in drought and prevent frost damage in winter by mounding the soil.

Various techniques have been devised some of which are based on natural regeneration (e.g. tip layering) and others are unnatural. In a home garden, layering is usually performed to produce a few additional shrubs, perennials and occasionally herbs. Houseplants may be propagated by air layering, although this technique is not confined solely for this use.

There are a number of different layering techniques used: tip layering, simple layering, serpentine layering, mound or stool layering, and air layering.

The advantages of layering include:

1. A wide range of plants may be propagated by layering – including some very difficult to root cuttings, e.g. Corylus (Hazel).

2. Not much skill or equipment is required – this permits the propagation of some plants where other techniques require specialised equipment.

3. A large plant may be produced in a fairly short time.

The disadvantages include:

1. Layering is an expensive method, because much land and labour is required and there is no mechanisation method available. Not issues for the home gardener, but these are issues for commercial growers.

2. Inefficient use of propagation material. A single stock plant may only produce a very limited number of new plants – limited by the number of suitable branches available on the stock plant and the area around the stock plant.

3. The commercial grower, with established stock beds may find them difficult to maintain and cultivate.


Tip Layering

Tip layering is the technique used to propagate some members of the Rubus genus (including blackberries and loganberries). This method takes advantage of the plants within this genus to root from stem tips that touch the soil. Brilliant in its simplicity, blackberries (will do it with no encouragement at all. Other members of the Rubus genus that are propagated this way include Rubus biflorus, R. cockburnianus, R. coreanus, R. phoenicolasius, R. ulmifolius, R. linkianus and R. thibetinus.

Late in the summer, a vigorous, healthy shoot of the current season’s growth is bent downward. At the point where the shoot tip will touch the soil, prepare a slanted trench about 15 cm deep. This trench should be shaped so that there is a sloping side at the edge closest to the parent and a vertical side at the edge furthest away from the parent plant. This configuration is recommended because it not only permits the shoot to be buried without breaking but it also encourages the formation of new growth upwards. Bury the tip of the shoot (about 10 to 15 cm of the growth) into this trench and, if necessary, pin down the shoot so that it has good contact with the soil. Fill in the trench and keep the soil moist. The tip will grow down a little and then recurve to form a sharp angle and this is the site where roots develop.

The tips should develop roots within a few weeks. At this point, the new plant may be lifted, severed from the parent plant (usually leaving about a 15 to 25 cm “handle”) and either moved to a new location or potted up to grow on. The new plant consists of a terminal bud, a mass of adventitious roots and the “handle”. New plants require some special attention while they adjust to independence from the parent plant – the compost or soil should be moist (but not wet) and they should be given protection from the extremes of both temperature and light. For those layers produced with weak root systems, some overwinter protection may be desirable (for example, being grown in the protected environment of a cold frame).

In a commercial setting, stock plants are spaced about 3.5 metres apart. The mother plants are cut back to 20 cm when planted. The resulting new growth is trimmed back (when a “rattail” phase occurs) to encourage even more shoots (each of which is a potential tip layer. After harvesting of the new plants, the stock plant is cut back to about 20 cm to initiate new shoots to be used the next season. Using this technique, a stock plant may be productive for about 10 years.

Figure 69 Tip Layers

new plant in 3 4 months

branch of parent plant

soil level

shape of trench

side towards parent plant


Simple Layering

Simple layering is often practiced to produce new plants from a wide range of shrubs (particularly those that produce multiple shoot systems such as Corylus) and some prostrate herbaceous perennials (for example, border carnations Dianthus cultivars).

This form of layering is often considered to be the most common form of layering. Vigorous, one year old shoots should be encouraged to develop near to the soil’s surface – this may be the result of such practices as coppicing or other hard pruning activities.

Like tip layering, the stems of the shrubs (or herbaceous perennials) are bent down to the soil and pinned down into a shallow trench. The steps involved are:

1. at the location where the shoot will touch the ground, dig a trench about 10 to 15 cm deep

2. trim away the leaves from the shoot that occur between about 10 to 40 cm behind the shoot tip

3. bend the shoot and pin it down into the bottom of the trench – ensuring that the top of the shoot will be well above ground (perhaps 8cm or so above the surface when the trench is refilled)

4. fill the trench, and firm and water the soil 5. keep the soil moist but not saturated

Although the described technique uses a trench and either wire staples or wooden pegs to pin down the shoot, another technique pins the shoot to the top of the soil with a weight (like a brick).

Unlike tip layering, in simple layering the shoot tip is led up as near to vertical as possible. After bending, the shoot is covered but leaving the tip of the shoot exposed above the soil’s surface.

Figure 70 Simple Layering

In simple layering, the end portion of the shoot should have a sharp bend about 15 to 22 cm back from the tip. This acute angle created is often sufficient to encourage root formation.

However, sometimes other treatments are performed at this bend to encourage rooting – these include:

1. Removal of a ring of bark at the lowest end.


2. Cutting inward and upward to form a projecting tongue. 3. Binding copper wire around the stem to form a constriction point. 4. Cut and twist to girdle stem.

Figure 71 Cutting to Form a Tongue

Both the bending of the stem and these wounding techniques may help encourage root formation by restricting the flow of sugars and hormones, created at the leaf (through photosynthesis), back down the stem to the rest of the parent plant. In many cases, these wounding techniques are not necessary, and may provide an entry point for diseases.

Dormant, oneyearold shoots are best (at this time, these shoots should still be flexible enough to be bent and manipulated successfully). Suckers produced near the crown root more readily. Whenever possible, anticipate the need for growth near the surface of the soil and prune back a low branch so that young shoots will be produced in the desired location.

Ideally, the soil around the parent plant should be well drained (with the addition of some grit) but with good waterholding properties (through the addition of organic matter, for example peat or wellrotted garden compost or coir). These two amendments would ensure that the rooting area has both good moisture retention and good aeration – both essential for the growth and development of roots.

In late winter or early spring, as soon as the soil may be worked, the process may be started. For subjects like Rhododendron and Magnolia, it is best to use the growth later in the growing season when it becomes more pliable.

Perennials may be layered in the spring, just before new growth begins, or may be layered in autumn after new growth has ended for the year. Nonflowering shoots should be used. Perennial herbs (like trailing forms of Rosemary, Rosmarinus officinalis and thyme, Thymus sp.) may also be propagated by layering.

With spring layering, rooting may well be enough advanced for severing the new plant from the parent plant during the autumn. Shortly after the new plant is severed from the parent (often about three to four weeks later), the shoot tip may be removed to encourage more growth of the roots. If sufficient root has developed at this time, then it may be lifted at this point – either to be potted up or to transplant into a new location. Those plants without sufficient root in the autumn may be lifted in the following spring or autumn, once additional roots have formed successfully.

Usually evergreen plants should be potted and kept humid and cool for several weeks. Deciduous species can be planted in nursery rows. Although some defoliation may occur, recovery in spring usually occurs.

Commercial operations that maintain stock plants should locate them far enough


apart so all shoots can be layered (completely encircling the parent plant). The longevity of stock beds, if adequately maintained, is around 15 years.

Serpentine or Compound Layering

Serpentine layering is nothing more than a series of simple layers being produced using the same stem. It is an especially useful technique for propagating plants that produce long shoots in a single year. Many vines are examples where serpentine layering is a suitable propagation technique – including Wisteria, Vitis, and Clematis. The advantage of serpentine layering is it permits several new plants (or layers) to be produced from a single shoot.

This technique is suited to a home gardener with ample space to permit the trailing of long shoots over the soil’s surface. Serpentine layering is not used commercially.

The steps are simple: 1. A long growth is pegged down to the soil and the stem is arched behind the

bud. 2. The shoot is alternately exposed and covered along its length. Each

exposed part should have as a minimum one bud and each buried section will form adventitious roots. The buried portions may be wounded prior to being pegged and then covered in soil. Rooting hormone may be applied to the wounded areas to encourage root formation.

3. The soil must be kept moist to encourage root formation. Energy from the parent plant is used to assist in the formation of the roots.

4. After root formation has occurred (usually by autumn of the same year), cut the shoot into sections – each with a rooted portion and a shoot portion and grow on just as those produced by simple layering.

Figure 72 Serpentine Layering

Stooling or Mound Layering

Stooling or mound layering is a technique used by commercial growers. It is used particularly for the production of rootstocks for the use in grafting.

The principle exploited by this technique is the production of roots from stems as a result of etioliation and blanching (the elimination of light from the growing shoot – please see earlier in this lesson for an explanation of etioliation as it applies to the development of adventitious roots).

This technique uses stock plants. A stock bed is carefully prepared of loose, fertile

site of future shoot

one plant one plant

shoot tip


soil. Healthy stock plants are selected and set into this bed. These stock plants are permitted to grow for about a year – establishing an adequate root system. Spacing in the bed is critical because soil between plants may be used to create mounds over the plants (although sometimes additional soil is brought into the bed to achieve this). Individual plants growing in containers can be also be stooled. Stool beds are productive for up to 15 years.

In late winter or early spring, the plants are severely pruned back (to about 2½ to 5 cm above the soil level) and, as a result, produce many strong coppice shoots. The new shoots are permitted to develop to about 10 cm and then are covered with moist soil (or other light substrate, like coir, sawdust or a combination of soil with these ingredients) to about half their height. This operation continues throughout the first half of the growing season – as the growth continues, so does periodic mounding so that half of the new shoot is above the soil and half below the soil’s surface. This process stops in midsummer (at this time, the shoots have been covered in about 15 to 20 cm of soil).

During the remainder of the summer, adventitious roots form at the base of the new shoots. At the end of the season, the rooted shoots may be cut away from the parent plant and potted on. At this time, the parent plant may be discarded or used to produce new stools next year. The new shoots will be grown on in precisely the same way as those produced by other layering techniques – receiving adequate moisture and some protection from extremes of the weather.

Figure 73 Mound Layering

In the home garden, this technique may be used to propagate quinces (Chaenomeles cultivars), Smoke bush, Cotinus coggygria and some herbs are also propagated this way – including lavender, Lavandula spp., and sage, Salvia officinalis.

original soil level

layers of soil are mounded up over the stock plant

during the growing season

roots develop at the base of the new shoots

soil levels at different times of the growing

season

the additional soil is carefully removed to reveal the rooted

shoots which may be severed at the base of the shoot and potted on or lined

out (planted in rows) in a nursery bed


Air Layering

Air layering is also called Pot layerage, Chinese layering, Circumposition, Marcottage and Gootee. This technique is one of the oldest forms of vegetative propagation still used today. However, today this technique is not used very frequently.

When it is not possible to bring the stem to ground level, air layering is one method that may be used. It can be a useful technique when only small numbers of plants are required and where the special care required by this technique may be managed. It is a method that is most appropriate for humid environments but if appropriate care is taken, it can also be successful in drier climates.

This system is often used for subtropical trees and shrubs (for example, some house plants) but is also a valuable method for the propagation of smooth barked Rhododendrons. Some plants that are commonly propagated by air layering include mango, Ficus spp., Citrus and avocado. Other plants propagated by air layering include: Ilex, Syringa, Azalea and Magnolia but these are best left for two seasons to ensure adequate root formation.

The basic steps involved are:

1. Select a suitable shoot – remove any leaves from this shoot that occur about 15 to 30 cm behind the tip.

Carry out air layering in spring with previous seasons' shoots, especially those with just a few leaves developed.

2. At the point where rooting is desired wound the stem – at the site about 15 to 30 cm behind the shoot tip.

This may be done by girdling – by removing a strip of bark 1 to 2½ cm wide around the stem. Or slit at an upward angle – usually a cut about 5cm long is made and kept apart through the use of a small wedge, like a wooden matchstick or by inserting moistened sphagnum moss.

3. Dust the point of injury with a rooting medium – this is particularly necessary when dealing with difficult to root plants (for example Rhododendron).

4. Prepare some handfuls of sphagnum moss by moistening and knead it into a ball shape, then stretch it into a shape that will cup around the stem.

5. Place this moistened (but not wet) sphagnum around the wound in the stem and hold this in place with a square sheet of black polythene (about 25 cm square) – secure with tape.

The polythene must have a high permeability to gases including carbon dioxide and oxygen. It should also have low transmission of water vapour and be long lasting.

Place 'fold' on lower side. The polythene should be sealed by tying firmly with insulating tape. Ingress of water must be prevented; otherwise fungal rots may occur. Support the layered shoot with a cane or other shoot.


Although rooting can be viewed through the transparent film, light entering the sphagnum may deter rooting of the shoot. I may be necessary to renew the polythene after 2 to 3 months.

6. If any growth occurs on the shoot being rooted, trim it back at the end of the dormant period. Eventually, when rooting has occurred successful, it is time to remove the shoot from the parent plant. It is best to leave the shoot on the parent plant until the dormant period. Cut below the point of layering, remove the polythene, loosen the sphagnum, and pot up using a potting compost. It is usually best to grow these new plants under humid conditions for 2 to 3 weeks.

Figure 74 Air Layering of Scindapsus aureus

? For you to find out …

1. When would you divide herbaceous peonies (Paeonia spp.)?

2. How would you propagate Ginkgo biloba?

3. How are named cultivars of lilac (Syringa spp.) propagated?


Plant Division

Plant division is the technique of separating one plant into many smaller plants – each of which has its own root and shoot system. Many plants are easily divided because their natural growth pattern is to produce a mass of shoots (forming what is called a crown) – each with its own root system.

Not all plants may be propagated by division. For example, many taprooted perennials (for example, lupines, Lupinus spp.) are not suitable for propagation by division.

leaf stalk

stem

polythene wrapping

sphagnum moss within the wrapping


However, many herbaceous perennials may be propagated by division – and in the home garden, this is a fairly simple method of increasing the number of plants. Most commercial operations do not routinely use this method because the number of plants produced from each parent plant is relatively small.

Usually herbaceous plants are divided when they are not actively growing – this reduces the stress on the new divisions (since they may not have an adequate root system to support growth or a large amount of foliage at this time). In general, springflowering herbaceous perennials are divided in the late summer or autumn while summer or autumn flowering perennials are divided in the spring.

Special care must be taken when dividing evergreen perennials (such as Liriope and Carex). The leaf area must be trimmed to reduce moisture losses through transpiration because the initial root system may not be large enough to support the leaf area.

The key to producing viable divisions is to ensure that there is more root to each section than shoot.

Following division, the new plant will require a period of adjustment – to repair damaged roots and reestablish shoots. During this time, the plant may require some protection from intense light (that is, some shade) and additional water may be beneficial in assisting the new division to establish itself.

There are a few different methods used to divide plants:

1. The separation of offsets is a technique of division used for:

• the removal of offsets of bulbs, • removal of pseudobulbs, • removal of small plantlets that develop at the base of parent plants

2. Herbaceous perennials with fibrous root systems may be dug up and either pulled apart or cut apart. Herbaceous perennials with fleshy roots (for example, Hosta and Helleborus) may require a little more attention but may still be propagated by division of the parent plant crown.

3. Some woody shrubs and small trees (for example Aesculus parviflora, Kerria japonica) produce clumps of growth from suckers produced below the soil from the parent plant. With care, these may be severed from the parent plant and removed to make new plants.

4. Many bulbs, rhizomes or tuberous roots may be separated – each piece producing a new plant. Iris, Bergenia and Dahlia are examples of the plants that may be propagated this way.

Division of Offsets

Many plants produce offsets, including many herbaceous perennials (for example, Sempervivums and auriculas, Primula auricula) and some semiwoody perennials (for example Yucca filamentosa). An offset is a small plantlet or side shoot that develops from the parent’s main root. When ready to be separated from the parent plant, they have already developed their own root and shoot system.


Case Study of Offset Division: Primula auricula

Primula auricula produce offsets throughout the growing season. Some cultivars start producing these offsets starting in the first or second year of independent growth (that is, from the time they were removed from their parent plant). Some cultivars produce many offsets, but others produce perhaps only 2 or 3 per year.

The separation of offsets of auriculas is performed in early to midsummer (this is after the plants have flowered) – these pictures were taken in midJuly. Offsets taken at this time may be ready for sale, in a commercial operation, from October onwards. This parent plant has four offsets (only 2 are clearly visible in this photograph).

Figure 75 Parent Auricula With Offsets

The steps taken to remove these offsets include:

1. knock the plant out of the pot, or carefully dig up the parent plant from the garden bed – try to avoid damaging the root system as much as possible (choose a day when the soil is lightly moist but not wet to do this)

2. shake the compost or soil from the root system 3. separate or remove the offsets – trying to preserve the root system as much

as possible

parent plant offsets


Figure 76 Separated Offsets and Parent Plant

4. pot the offsets and parent plant into a gritty compost (a multipurpose compost with added washed grit, in the ratio of 2 parts compost to 1 part grit, is usually ideal)

Figure 77 Pottedup Offset

These pots have been given a mulch of washed grit – this preserves soil moisture, prevent the growth of weeds (that may result in undesirable competition for the young plant) and is aesthetically pleasing (sometimes a valuable sellingpoint).

In this case, a controlled release fertiliser (Osmocote Plus) was incorporated into the compost before potting up. This fertiliser was included because these offsets are being grown by a commercial operation and it is essential that these plants grow quickly to reach saleable size. A home gardener may choose to add a controlled release fertiliser, may choose to water with a fertiliser solution later as the offset grows or may, instead, choose to select a compost with a higher nutrient composition – particularly phosphorus which is essential for development of root systems.

Offsets need not be potted up into containers. They may be relocated directly into a garden bed or may be placed into a nursery bed to grow on.

parent plant offsets 1

2 3

4 2 3


In all cases, it is essential that the offsets be watered in (to settle the compost or soil around the roots). These new plants must be kept moist (not wet) initially while the root system adjusts to its new, independent status.

5. place the newly potted offset into a cool, shaded location (a shaded greenhouse is one option).

Figure 78 Growing on Auriculas

Ensure that the offsets receive adequate moisture, nutrients, and may grow free from the competition of weeds and pests or diseases. Ensure light levels are lower than that of the parent plant initially – gradually, the offsets may tolerate greater light intensities and may endure more environmental stresses.

In the case of offsets being grown on directly in garden beds or nursery beds, some protection from weather extremes is desirable. For example, some shade will reduce the light intensity that these young plants are subjected to and less exposure to drying winds. A temporary lath structure or shadecloth suspended over the plants (in a tunnel arrangement perhaps) may be two alternatives.

The key is to avoid stressing the newly independent plants. Excess light and heat will mean that the leaves will transpire rapidly – this leads to a loss of moisture that the small root system may not be able to supply. The result may be temporary wilting of the offset – although the plant will recover from this wilt, the time spent wilted is time the plant cannot photosynthesise to produce the food to fuel new root and shoot growth.

In periods of cold, additional protection may be required – this may come in the form of a cold frame or the use of cloches or horticultural fleece. Offsets, with their reduced root system, need to be kept moist during the growing season. Protection from the competition of weeds is essential if the offset plants are to produce maximum amounts of food, by photosynthesis, for growth.

This greenhouse has been shaded with 50% shade cloth.


If growing the offsets in containers, these may require some protection from temperature extremes – wintering in cold frames and sinking the pots into the soil to prevent overheating during the summer. Especially tender divisions may require a heated greenhouse for overwintering.

Division of Crowns

Many herbaceous perennials, as a consequence of their natural growth patterns, produce crowns of short or buds – each with an independent, functioning root system. Examples include Lilyofthe Valley, Hosta, chrysanthemum and aster.

Plants that produce fibrous root systems are the ones most easily propagated by division. The parent plants are lifted, damaged and dead portions are removed, surplus soil is removed, and the remaining crown is washed (this permits the gardener to view where the best locations for divisions naturally occur). Only wash roots if this is essential as the recovery of the plant may be hindered by the loss of many of the fine roots.

Some plants are suited to being separated by hand (the roots and shoots are loosely intertwined), some require the use of knives or border forks or even machetes to divide.

After cutting, the cut areas may be dusted with a fungicide to prevent the entry of diseases into the exposed areas of the root.

The most important point is that each section must have an adequate root system to support the top growth. Each division must contain at least one shoot or bud and that adequate roots support each piece. Stronger divisions produce plants that re establish fastest. Weaker divisions may require some additional care and protection to ensure that the division survives.

The time of dividing varies. The goal is to divide the plant’s crown just as active shoot growth commences – this will permit the vigorous portions to be identified. For some springflowering species, this time may be immediately after flowering has finished. For some summer and autumn flowering species, this may be in late winter or early spring – just as new growth commences.

The divisions must be potted up or planted in the garden beds quickly after the division has occurred. This will result in the least amount of drying to the exposed, tender roots. Once offsets have been planted, they must be watered in to ensure adequate contact between the compost or soil and the roots. If a division includes a tall stem, this should be cut back to reduce the amount of moisture that will be lost by the new plant. The after care of these divisions is identical to that of the divisions produced from offsets.

Division of Suckers

Some shrubs are particularly good at producing suckers – these are plants that arise from below the ground that originate from the roots or underground stems of the parent plant. In these situations, some of the suckers may be removed and planted up to grow as independent plants. This is another form of plant propagation by division. This method is suitable for the propagation of Kerria japonica.


This method is not always suitable for the propagation of grafted plants – propagation of suckers from grafted plants will propagate the root stock plant.

Although this operation may be carried out at any time of the year, the ideal time is usually during the dormant season or when the plant is not actively growing. Early spring is often the best time because the soil is moist, air temperatures are cool (resulting in lower stresses on the newly separated division), but soil temperatures are beginning to warm. Suckers that have developed into a small clump of stems may be removed from the parent plant.

The steps involved are:

1. Locate an underground stem that has suckers growing on it. 2. Carefully dig and lift it – avoid disturbing the parent plant as much as

possible. 3. Confirm that the sucker has some fibrous roots at the base of the sucker –

without these roots, the removal of the sucker would not be division (it would be a cutting). If fibrous roots are absent, the sucker may be returned to the soil, firmed in and let grow on until the roots form.

4. Cut the suckering stem using a sharp pair of secateurs – make the cut as close to the parent plant as possible.

5. Replace the soil around the parent plant and firm it in. 6. Cut off the portion of the underground stem between the parent plant and the

fibrous roots below the sucker and decided if the sucker may be divided further into more plants (each new plant must have its own fibrous roots and a shoot).

7. Plant up the divisions – in a nursery bed, in the location where they are to grow (this is an option for very vigorous suckers), or pot them up for growing on. Water in the division.

8. If the sucker is long, trim it back (the goal is to ensure that there is enough root to support the shoot – when in doubt, trim back the shoot to avoid stressing the cutting).

The after care for these types of divisions is the same as that described earlier for offsets.

Division of Bulbs, Rhizomes and Tuberous Roots

The term “offset” is also used to refer to the bulbs produced within the parent bulb’s outer covering (or tunic). This is a natural way that many bulbs reproduce.

Bulbous plants are usually best divided once they are dormant (after flowering has completed, and the foliage has naturally died back). When bulbs are evergreen, the best time to divide is immediately after flowering.

Offsets are attached to the basal plate (the origin of the bulb root system) – sometimes the offsets are to the side of the parent bulb (for example Daffodils, Narcissus spp.) or below the parent bulb (for example, Tulips, Tulipa spp.). The basic steps are:

1. Carefully dig the parent bulb and clean off the soil (avoid damaging the bulb and offsets as much as possible).

2. Detach the offsets – this is often easily done by hand, but occasionally a sharp knife may be used.


3. Dust the cut surfaces of the parent bulb with a fungicide to protect it from rot 4. Replant the parent bulb – at the original depth it was growing. 5. Larger offsets might be capable of flowering the next year, and may be

planted directly into the garden bed. 6. Smaller offsets may need to be grown on before they reach flowering size.

This may be accomplished in a nursery bed, or in pots. They may require two years of growth before they are large enough to flower and may be planted into the garden beds for display.

Rhizomes are propagated by division. Usually the optimum time is usually just after flowering has finished. In the case of bearded iris (Iris germanica), regular division not only results in the propagation of new plants, but is also essential to prevent overcrowding and to maintain flowering. The basics are the same as for division of crowns – the plant is carefully dug up (usually a garden fork is used to limit damaging of the root) and the soil is shaken off. At this point, the rhizome may be broken into new sections (each with a piece of healthy rhizome, a small fan of leaves, and some fibrous roots). Cut sections of the rhizome may be dusted with a fungicide. Finally, the foliage should be trimmed to about 15cm high – this reduces stress on the newly independent plant and reduces the chance that wind may shift the rhizome division in the soil. Finally, the new division is replanted. Usually a slight ridge is formed in the soil with shallow trenches on either side. The rhizome is placed on this ridge with the fibrous roots being directed into the two trenches. The soil should cover the fibrous roots and leave the upper surface of the rhizome exposed to the sun. Watering in is essential. All other after care is identical to that already outlined for offsets earlier. Plants that develop rhizomes useful for propagation include Arum lily, canna, asparagus and the weed, ground elder.

Tuberous roots of Dahlia are also frequently propagated by division. In this case, division occurs in early spring, just before new growth commences. If the Dahlia roots are left in the ground overwinter, they must be carefully dug. If Dahlia roots are stored overwinter, then they must be removed from storage. Each division must contain:

• a healthy, dormant bud – often these buds (or “eyes”) are near the old stem, and appear as small pink bumps in the upper surface of the tuber,

• a healthy tuber. Sometimes it is best to wait to perform the division of Dahlia tubers until the buds commence growth, but only slightly. Then these more obvious buds may be the clues to where successful divisions may occur. Once the locations of the division cuts are identified, a sharp knife is essential to separating the divisions from each other. After division, the cut areas may be dusted with fungicide. At this time, the division may be replanted. Follow on care is comparable to that of already described for offsets.

Figure 79 Segment of Bergenia Rhizome That Will be Used to Generate a New Plant

piece of Bergenia rhizome about 3.5 cm long


Activity

Choose three or four plants with which you are familiar. In your Journal, note how you would go about propagating these. Be as detailed and specific as you can, doing further reading if necessary. Include diagrams to illustrate your chosen technique.

If you have access to any specimens, in your garden for example, make plans to try out at least one of these techniques. Note suitable dates in your Diary.

Budding and Grafting

This is the union of two plants. It is popular with nurserymen as a technique to produce uniform batches of plants, which are difficult to root as cuttings. In the next section, the details of budding and grafting will be explored.

? Answers to Self Check Questions on page 111

How would you propagate perennial Phlox to obtain a stock free from eelworm?

Perennial phlox is propagated by root cuttings. These can be cut into lengths of 35cm in winter, laid flat in a container in a frame, and covered with 710cm of soil or 'pea grit'.

? From page 122, were you able to find out that …?

1. Herbaceous peonies (Paeonia spp.) are divided in late September or early October.

2. Ginkgo biloba is propagated by seed or cuttings.

3. Named cultivars of lilac (Syringa spp.) are propagated by cuttings or budding on to common lilac (Syringa vulgaris) or privet (either Ligustrum ovalifolium, California Privet, or L. amurense, Amur privet) but this is less satisfactory because of suckers.


5 BUDDING AND GRAFTING

By the end of this section, you will understand the use of budding and grafting for the propagation of plans:

• Define the terms budding and grafting. • State the reasons for use of budding and grafting for

the production of particular plants.

Introduction

Put simply, grafting is the unification of two plants. It is another form of vegetative propagation but this one involves pieces from two (or mode) different plants that are joined to form a new plant.

Grafting techniques are used frequently in commercial production. In a home garden, it is used less frequently but still has a role to play for experienced or adventurous gardeners. Although home gardeners may not perform grafting themselves, they may purchase plants that were produced by grafting techniques and these may require some special treatment to ensure the plant remains vigorous over time.

Shoots that form above the graft union have the characteristics of the scion. Shoots that form below the graft union have the characteristics of the rootstock.

It is more common for two portions to be joined together. However there are times when three or even more can be used. A third plant added between two others becomes the trunk or a portion of it and is termed an interstock. Multiple grafts may produce an apple tree with several cultivars.

Scion

The name of the portion that develops into the top portion of the plant is called the scion. The scion is usually chosen for some quality – examples include fruiting characteristics (taste, disease resistance, quantity, size) in the case of fruitbearing trees or flowering characteristics (amount of flower and size and colour) in the case of ornamental trees or shrubs.

Stock or Rootstock

The name of the portion that contributes the root portion of the new plant is called the stock or rootstock (or sometimes, understock).

A particular rootstock may be used for a number of reasons but the particular scion species and cultivar will govern primarily the choice. A carefully selected rootstock can provide wellanchored root systems, toleration to soilborne diseases and adaptability to certain soil conditions. It can also modify the growth and vigour of the scion, alter the habit and size of the plant and by modifying the vegetative / floral balance of the scion it can promote both flower and fruit production.


Seedling rootstocks can be advantageous in that they are easy to produce, do not generally carry viruses and the root system may be stronger. However there can be considerable variation in seedling rootstocks, which can lead to variability in growth. To avoid this, careful selection is required.

Grafting and Budding

There are many different type of grafting. Usually the general term “grafting” applies to those situations where a portion of a stem of one plant (the scion) is attached to a second portion of a plant that has a developed root (the stock or rootstock). Normally, a graft involves a length of scion wood (often of 30 cm long with perhaps 6 or more buds).

Figure 80 Example of a Graft

“Budding” is name given to a special form of grafting where the scion consists of a bud only. This technique of using only a single bud is sometimes used when only a small amount of scion material is available to produce a larger number of plants. Budding is commonly used for the production of roses and many woody plants.

Why Graft and Bud?

There are four main reasons for grafting and budding:

1. Grafting is used as an alternative method to reproduce cultivars that do not root readily from cuttings or other vegetative means. If vegetative reproduction is essential to avoid the variability of seedgrown plants, and the production of new plants using cuttings is not viable, then grafting may be the only method suitable for creating new plants. Some situations include:

• Fruit trees: apple, pear, plum, peach, cherry

This pear tree is the result of a graft – note the swollen graft union.


• Roses • Speciality conifers – Abies, Picea • Speciality oaks, beech, sycamore and wisteria, and sometimes clematis.

This list used to be much longer because grafting was the only commercially viable method of producing the desired numbers of plants of many species that were not produced from seed and where cuttings were very difficult to root. However, as mist and fog techniques have been developed, this has reduced some of the propagation problems associated with some plants. For example, Clematis and Rhododendron are now more commonly grown from cuttings in a commercial setting.

An additional advantage is that grafting may produce a mature plant in a shorter time. In some cases, plants cannot be produced quickly from cutting or seed. In commercial operations, these plants may be produced more economically through the grafting of desirable scion material onto compatible stock tissue. In breeding programmes, the speed of producing mature plants may also be essential – in some situations grafting may help this process. However, these are issues for the commercial grower, not the home gardener.

2. Grafting also permits the qualities of two or more separate plants to be combined into one plant.

Grafting may allow the benefits of special rootstocks to be used. For example, an apple cultivar with a superior fruit that grows into an extremely large tree may not be suitable for growing in an orchard or in a garden. In this case, a scion from this apple cultivar may be grafted onto a “dwarfing” rootstock. The result will be a manageable sized tree that still produces the highquality fruit desired. Grafting may be the only method available to produce these desirable plants.

Figure 81 A Grafted Apple Tree

The table below lists rootstocks used by the nursery trade. It is being included for

the graft union


information purposes only and does not require memorisation for the RHS Level 2 examination.

Apple East Malling various rootstocks for the control of vigour

Merton Malling for controlling vigour and resistance to woolly aphis (EM rootstock X Northern Spy)

e.g. M9 dwarf, M7, M106 semi dwarf M111 vigorous. Pear Quince A and C for controlling vigour.

Seedling pear occasionally used especially for standards but some are incompatible.

Plum Myrobalan B, St. Julian, Pixy (dwarf) Peach Brompton, St. Julian A Cherry Most of the old rootstocks have been superseded by Colt Rose Canina seedlings, Rosa rugosa, R. dumetorum 'Laxa' Acer A. palmatum seedlings for cultivars of A. palmatum and A. japonica. Rhododendron Cultivars on to R. ponticum or R. decorum. Cultivars on members of the same

species.

The qualities that the root stock may contribute include: • dwarfing, as described above (for example, M27 is the most dwarfing

rootstock), • disease resistance (for example cherries where colt and cob rootstock are

resistant to bacterial canker), • tolerance of soil conditions (for example, roses used in greenhouse

production of cutflowers often are budded onto rootstocks that tolerate dry, shallow soils).

Sometimes grafting is used to produce fruit trees with scions from different cultivars. Normally fruit trees benefit from being grown with nearby trees of different cultivars so that crosspollination may occur. When space is tight, a single tree may perform the work of multiple trees if multiple cultivars are grafted onto a single rootstock. In this case the flowers from one cultivar may cross pollinate the flowers from another – all within one plant.

3. Grafting may be used to change the cultivar of established plants

Again, this is a situation for the commercial grower. If established, healthy plants produce fruit that is no longer in demand, the cultivar may be changed by a process of grafting called “topworking”. This procedure permits the plants to reach maturity faster than if the existing plants were removed and replaced with new plants of the desired cultivar.

4. Repairing damaged trees

In some cases, trees with damaged bark (from vandalism, poor cultivation practices or animal injury) may be repaired through the use of some specialised grafting techniques, including:

• For arching with additional rootstocks. • Bridge grafts to help when sheep or rabbits have eaten away the bark

tissue and girdled the tree.


The Limitations of Grafting and Budding

Only plants that are closely related can be grafted. The stock and scion must be compatible.

Dicotyledons lend themselves to grafting because of the continuous cambium and related tissue. However monocotyledons have a scattered arrangement of vascular bundles and little or no secondary thickening – this makes the alignment of the vascular tissues in the stock and scion very difficult although there are cases where successful grafting of monocotyledonous plants occurs.

Incompatible grafts may not form a union, or the union may be weak. A poor union results in plants that grow poorly, break off or eventually die.

The compatibility of plants has been determined through many years of trial. The closer the plants are related, the greater chance the graft will be successful.

• Most varieties and cultivars of a particular fruit or flowering species are interchangeable and can be grafted.

• Plants of the same botanical genus and species can usually be grafted even though they are a different variety.

• Plants within the same genus but of a different species may often be grafted, but the result may be weak or shortlived, or they may not unite at all.

• Plants of different genera within the same family are less successfully grafted, although there are some cases where this is possible.

• Plants of different families usually cannot be grafted successfully.

Some plants are just not good candidates for grafting. The plants that graft well are those that produce a substance (which is sometimes referred to as 'wound gum') that forms a seal on exposed xylem vessels. Plants that do not produce this ‘wound gum’ are more difficult to graft.

Plant health plays a role in determining if a graft may be successful. All material used in budding and grafting should be free from pests, diseases and viruses. Virus infected material is known to reduce the percentage of successful grafts. Fungal infections of the wounds made during the grafting process can be frequent unless adequate precautions are taken.

It is sometimes believed that two plants can be made into a genetically different plant by the process of grafting. However, there is no basis for this idea. Although there are cases where a different type of shoot develops from the graft union, this is the result of a chimera, a type of mutation. This is not a true intermingling of the genetic structure of two different plants as occurs in seedproduced hybrids.

Graft Incompatibility

When the two pieces of the graft do not form a successful vascular connection, this is


called graft incompatibility. The stock and scion do not unite.

If the union is compatible then the point of join should be as mechanically strong as the tissue above and below. This may be caused by a breakdown in the phloem tissue

If the union is failing, then the following symptoms may appear: • Corky tissue appear between the scion and rootstock • The scion deteriorates showing yellowing foliage and dieback. • Irregular swellings may appear at the point of the graft union. • The graft union may break – often with a sharp, distinct break between the scion

and stock tissues. • The vigour of one part of the union (either the stock or the scion) is much different

than that of the other. For example, the rootstock may form a number of suckers (below the graft union) while the scion languishes.

Figure 82 A Compatible Graft Union with Different Growth Rates

There are many reasons why the graft fails – some of these are: • the stock and scion were not compatible • the cambium of the two tissues were not meeting adequately or had shifted

following tying so that the cambium tissues were not in contact • the tissues of the scion or stock were in poor condition (for example, the

scion had been permitted to dry out), or were infected with diseases • grafting was done at the wrong time of the year • the graft was permitted to dry out • the scion had been in active growth at the time the graft was attempted and

the stock was not able to provide adequate nutrition to the scion tissue to support this growth

Tools and Materials

Grafting and budding require a number of specialised tools. Some of the more frequently used tools include:

• Knife

A goodquality knife, able to hold a sharp straight edge, is the key to good grafting. Although special grafting and budding knives are desirable, almost any good pocketknife can be used. A budding knife has special “spatula” that helps


during the lifting of the bark of the rootstock.

Figure 83 Budding and Grafting Knives

• Grafting Wax

Grafting wax was commonly used to seal the graft union to prevent the entry of pests and diseases and to prevent the tissue from drying out. The use of waxes has reduced as the use of transparent polythene grafting tape has become more popular.

There are two main types of grafting wax: o A hand wax is most commonly used for home grafting. It is softened by

the heat of the hand and can be easily applied. o Heated waxes are for commercial use and may be brushed on, but the

temperature must not be too high. Excessive heat will damage the tender cambial tissue.

• Grafting Tape, Budding Strips and Patches

Grafting tape serves two purposes: o It can be used to ensure that the two pieces of the graft are immobile –

enabling the callus tissue to successfully grow together. o It can be used in place of waxes to prevent the entry of pests and diseases

into the exposed tissue of the graft and it can prevent moisture loss through these tissues.

Traditionally this was a special tape with a cloth backing that decomposes before girdling can occur. Polythene tapes are now more commonplace although in some situations they must be cut and removed before girdling can occur.

Tapes may be used for binding grafts where there is not enough natural pressure. lectrical and masking tapes are also used. Masking tape may also be suitable where little pressure is required, as in the whip graft.

Budding strips are elastic bands. A budding strip looks like a wide rubber band that has been cut open so that it is no longer a loop.

Budding strips are used to secure the union between the stock and scion (make sure that the scion piece does not move). Although they are used for budding (where the scion is small), they are also used in other types of grafts with small stocks and scions.

general purpose grafting knife – note the straight blade

budding knife – note the “spatula” on the top edge that helps lift the bark flap


Budding patches are rubber patches that are tied around the bud after it has been inserted into the rootstock. These patches have the advantage of applying pressure evenly around the bud to assist in the union of the bud to the rootstock and they gradually deteriorate and fall away (preventing any girdling).

Formation of the Graft Union

How Graft Unions Form

The formation of a graft union is based on the natural wound healing activities of both the scion and stock. Because the scion tissue is fresh (it must be newly cut), it is capable of meristematic activity when it is placed in close contact with the newly cut tissue of the stock. If the conditions (i.e. temperature and humidity) are conducive, then the exposed cells will become active. The formation of a graft union involves the following 4 basic steps:

1. In the first stage both the stock and scion will produce separate callus tissues (parenchyma cells) in the region of the cambium tissues.

2. These callus tissues will intermingle and join.

3. This is followed by the differentiation of certain of the parenchyma cells of the callus to form new cambium (cells which act like a bridge and connect the old cambium cells with the new).

4. The final stage is the production of new vascular tissue by the new cambium, which will then permit the passage of water and nutrients between the stock and the scion.

5. Later, when the cambium has made a good bridge of callus tissue, new lignified xylem cells will be produced. The long wood fibres, the vessels and tracheids will strengthen the graft union.

Figure 84 Graft Union

Closeup of the callus forming between the scion and stock

STOCK SCION

intermingled parenchyma (callus)

xylem of callus tissue

pith xylem

cambium

phloem callus

cambium of callus tissue

phloem of callus tissue

Cross section through a successful graft – the smaller scion on the left hand side and the larger stock on the right hand side.


How TBudding Unions Form

Budding involves a slightly different process: 1. The bud piece (scion) consists of the epidermis, cork layer, cortex, phloem

cambium and sometimes some xylem tissue of a dormant bud. This piece of tissue is laid against the exposed xylem and cambium of the stock.

2. Tbudding is only done when the stock plant is actively growing (so the bark “slips” as a result of the new cells being formed within the cambium layer). The bark is lifted so that the bud may be slipped in between the phloem layer and the xylem layer of the stock.

3. After the bud shield is inserted, a necrotic plate of material is released from the cut cells, and shortly after the budding process callus starts to develop and break through this plate.

4. The callus mainly comes from the rootstock (the bud does not have the resources to permit a large number of callus cells to grow from its tissues).

5. Once a continual layer of callus is made between the stock and scion it will start to lignify. This process is completed after about 12 weeks.

Essential Conditions For Successful Graft Unions

There are some important points to note about the formation of a graft union:

1. It is essential that the cambial tissue of the stock and the cambial tissue of the scion be in intimate contact.

2. Air moisture around the graft must be kept at a high level so that the tissues remains hydrated.

3. The graft or bud must be covered immediately after the join has been made so that no pathogens may enter the vulnerable tissue. This is done either by waxing or tying with polythene strips.

Traditionally, raffia is used to tie the stock and scion together (this is to ensure that the intimate contact between the cambial tissues remains intact) and wax is brushed over the entire graft to seal in the moisture and to seal out pathogens.

Environmental conditions following the grafting process can influence the development of callus tissue. For example, on apple trees the growth of callus is small below 0 o C and above 40 o C. Subjects that are bench grafted (grafted indoors or under cover at a bench) often exhibit increased callus formation if they are kept at high temperatures for a short time, but if the callus is allowed to develop slowly then a temperature of 8 to 10 o C is best.

Humidity is an important factor as the cell walls of the parenchyma cells which form the callus are thin and therefore subject to water stress. Turgidity of the cells will affect the formation of callus cells, which is why stock plants should be in a well watered condition before grafting and scion material should be freshly cut.

Oxygen is also necessary for a successful graft union as the rapidly proliferating cells are respiring. It is thought now that waxing can restrict air movement, and plants such as grapes are left uncovered by some growers during the formation of callus.


Grafting Techniques

This section will provide a brief introduction to some of the techniques involved in grafting. There are many techniques, each with advantages and disadvantages that lead to situations where these different techniques are most suitable. It is the goal of this section to introduce some common grafting and budding techniques and not to identify all possible techniques.

With dormant scion wood one can do whip and tongue grafts. This is very useful as a follow up from budding. For the nursery rows say 100 rootstocks were budded in July and only 70 took for whatever reason. In the period Dec to the end of March (and even April if the scion material is still dormant) it is possible to whip and tongue graft the failures. This could result in a much better percentage take growing out in their first nursery year.

Whip and Tongue Graft

Whip and tongue grafts are commonly used in the grafting of many fruit trees and some ornamental trees (Malus and Prunus cultivars). It is most commonly done in the field (as opposed to bench grafting that is done under cover in an easily controlled environment). In whip and tongue grafting, the ideal is to have the scion and rootstock wood of the same diameter (this helps in aligning the cambium of the two pieces).

The basic steps involved are:

1. Collect the scion wood

In midwinter, select healthy, vigorous cuttings from the scion tree. This wood should be from the previous season’s growth.

The cuttings should be about 20 to 25 cm in length – the centre of the shoot is used (not the tip or the base of the shoot). Each cutting should have 4 good buds, the lowest of which should be about 2 cm from the end.

If the graft is not to be made immediately, then bundles of these cuttings may be placed in a welldrained bed (leaving the top 5 to 9 cm each cutting above the soil level). This is necessary to keep the cuttings moist but dormant.

2. Prepare the rootstock plant

Just before bud break occurs in the spring, trim the rootstock plant. First, all side growths near the base are removed. Then the top of the rootstock plant is cut leaving about 15 to 20 cm above the ground.

Make a sloping upward cut beginning between 4 and 5 cm below the top. Remove a tapering, wedgeshaped piece from one side.

A second cut is then made vertically downward on the cut surface, beginning at a point 1/3 of the distance from the top. This second cut should be about 1/2 the length of the first cut and not just split along the grain of the wood (this is the tongue). A common fault is to begin the first cut too near the top, leaving too short a slope for tying.


Figure 85 Preparing the Rootstock

3. Lift the scion wood. Working the bottom of the scion wood, choose a bud about 3 to 40 cm from the base and make a cut on the reverse side of the cutting to this bud. Then make a second cut to match that made on the rootstock cut.

Figure 86 Scion Preparations

4. Insert the scion

The scion and stock are fitted together with the tongues interlocking. This is often done by slipping the scion wood over the stock wood in order that the two slices open slightly – permitting the tongues to fit together.

It is extremely important that the cambial layers match at least along one side, but preferably along both sides.

5. Secure the scion and stock

Bind the scion and stock together securely. This may be done using raffia (that has been moistened to make it most flexible) – this is the traditional approach. The alternative is to use grafting tape – a thin, transparent polythene tape that make be wrapped securely around the union (this also helps reduce moisture loss through the wounds and the invasion of pests and disease organisms).

If using raffia, applying wax will help protect the graft from moisture loss and from pests and diseases that may enter.

the view from the side

note presence of bottom bud

after the first angle cut is made, make the second cut


Figure 87 Joining Stock and Scion Wood

6. After care of the graft

Remove any growths that appear on the stock (these divert the flow of water and nutrition from the new scion wood). Once the graft has formed a successful union, cut and remove the ties that held the pieces together (if not removed, these may girdle the new growth). Usually a stake should be placed in position to support the graft and union because until a firm union is formed, there is a danger that the scion may be blown or knocked out.

There are some refinements of this basic technique – designed to increase the healing of the graft union. For example, a special notch called the “church window” is sometimes made to assist in the healing of the stock. These will not be outlined in this course.

This method is particularly useful for grafting relatively small material, 6 12 mm in diameter. It can be a highly successful method if properly done, as there is considerable cambial contact. It heals quickly and makes a strong union.

Budding

Budding is a special grafting technique in which the scion piece is reduced to a single bud. It is also called bud grafting. This grafting technique makes efficient use of cultivar material because a single cutting of scion wood (often called the bud stick) usually contains many buds – each of which has the potential of becoming a new plant using this technique.

There are two main types of budding – Tbudding (or shield budding) and chip budding. This lesson will only describe Tbudding. Tbudding is a common technique used for Roses and Apples and is sometimes considered the most suitable form of budding. Chip budding enthusiasts would probably disagree,

There is one constraint with Tbudding and that is the rootstock plant must be actively growing when the budding activity takes place. Tbudding relies on the new cell growth in the cambium that permits the cambium layer to be split apart (so that the bark (and phloem layer) may be lifted away from the xylem wood. When the bark easily slips, then the rootstock plant is in the right condition to receive bud grafts. Chip budding does not require that the bark “slips” and so may be performed when the rootstock is dormant.

slide the scion against the stock – pressing gently and carefully to open the tongues

longer cuts make the wrap more

secure

waterproof

wrap tightly to prevent moisture loss and to prevent the movement of the stock and scion


Tbudding is usually performed in the between the spring and autumn. For roses, midsummer is the best time. July and August are the best months for Pyrus and Prunus spp. Whenever possible, budding should be done during dull, showery weather – this reduces the stress that the scion bud undergoes

The basic steps for Tbudding roses are:

1. collect the scion wood

When Tbudding roses, the scion sticks are usually taken when the stems have started to flower, and the wood has started to ripen. Vigorous shoots should be selected from the desired cultivar.

The soft tip growth should be removed as well as leaves from every node. When removing the leaves, cut the petiole about ½ cm from the stem (this leaves this stub of a petiole to act as a “handle” for the bud shield).

These scion sticks must be kept cool and moist by wrapping in moist paper and keeping them in a cool place. Do not stand them in water because this might lead to the base of the bud stick rotting.

2. prepare the rootstock

Rootstock plants should be established. Rootstock plants may be purchased in the winter and then planted in early spring.

When preparing to Tbud, remove the soil from around the stem of the rootstock plant (it should be actively growing). Gently clean off the bark with a soft cloth. Find a spot where the bark is smooth.

Make a “T” shaped cut into the bark, about 2 to 3 cm below the top growth. Some prefer to make the horizontal part of the “T” first – this cut should be about ½ cm. Then the vertical part of the “T” should be about the same length and meet up with the centre of the horizontal part.

The cuts should be deep enough to cut through the bark, but not so deep that they cut deeply into the wood.

Figure 88 The "T" Cut on the Rootstock

3. prepare the bud (or bud shield)

the horizontal and vertical cuts

into the rootstock

the cuts after the bark has been lifted slightly


First remove the thorns from the bud stick – snap them off. Then insert the knife about ½ cm below a dormant bud (with stub of leaf stalk). Cut down and then scoop under the bud – leaving a “tail” at the top of the bud. This is the bud shield.

Figure 89 The Bud Shield

At this point, some people remove the wood from inside the bud carefully so that the contents of the bud are also not removed – leaving the green bark. Some people do not do this step and leave the sliver of wood inside the bud piece.

4. insert the bud into the Tcut

Carefully lift the flaps of the bark on the rootstock (this may be done using the “spatula” part of the budding knife). Using the tail of the bud, carefully slide the bud into the flap of the “T” on the rootstock plant. Make sure that the bud is pointing in the right direction (that is, not upside down). The stub of the leaf may be used to help position the bud within the “T”. Trim off the top of the bud tail above the “T”.

Figure 90 Insert Bud in the Rootstock

5. secure the bud within the “T”

The bud may be secured through the use of special rubber grafting patches (the rubber square is positioned over the bud and it is pinned together behind the

the bud before removal – note the

stub from the removed leaf

the start of the cut beneath the bud

the bud being removed from the scion or bud

stick the bud shield after

removal – this is the back of the bud showing the bark and bud initial

the inserted bud shield—including the stub of the old leaf and

the dormant bud

the T flap in the rootstock – before tying


stem). Budding strips may be used to hold the bud in place and hold the flaps down. Budding tape may also be used to do the same function.

6. grow on

The bud and “T” cut will heal over the next few weeks. The bud should remain alive but dormant until the next growing season. The rootstock plant should be watered and fed for the remainder of the season to ensure healthy growth occurs. The tie may need to be released to avoid growth constriction.

During the winter in harsher climates, the rootstock is often earthedup (to provide some protection to the new bud). When earthedup, this should be uncovered in the early spring. When still dormant, the rootstock should be cut off just above the new, dormant bud.

During the growing season, it is often wise to partly prune back the new shoot that results from the inserted bud. This will help establish a bushy shrub.

Another important type of budding is chip budding which is very useful for fruit trees.

Bench grafting is a term which is really about the location for the work. So while it is usual for roses and fruit trees to be budded in the field, it can be much more common that, for example, conifers would be grafted with a type of inverted graft where the short leafy piece of scion is inserted into the side of the stock plant – into a cut which enables the slim thinly sliced bottom scion (c. 30mm of the scion) cut on both sides to marry up with the meristematic tissues (or the rootstock).

Care of Grafted Plants

When a graft has formed successfully, the next step to consider is whether this graft union should be located above the soil or below ground.

In harsher climates, it is often advisable to position a plant so that the graft union is below ground. This provides an additional measure of protection to the graft to protect it from cold temperatures. In milder climates, graft unions are frequently left above the soil level because the need for additional winter protection is not necessary.

However, there are exceptions to this general rule. If the rootstock is providing certain characteristics to the plant then the graft union should be located above the soil level. If, for example, an apple tree consists of a vigorous cultivar for the scion wood and a dwarfing rootstock, then the rootstock’s influence on the growth of the scion is important. If the scion portion is permitted to form its own roots, the value of the rootstock would be lost. That is, the vigorous cultivar would form its own roots and would grow to the normal size – this defeats the purpose of grafting onto the dwarfing rootstock.

In some cases, for example Paeonia suffruticosa (tree peony) are difficult to root from cuttings and seed propagation does not lead to the production of plants with the desired flower colour and form. As a result, they are frequently grafted onto the roots of P. lactiflora (the herbaceous garden peony). However, the ideal situation is to grow a plant on its own roots. In this case this graft union is frequently placed below the soil level so that gradually the P. suffruticosa portion will develop its own roots to supplement that of the P. lactiflora root.


6 SAFE, HEALTHY AND ENVIRONMENTALLY SUSTAINABLE PRACTICES

Health and Safety

There are a number of situations in the propagation of plants where health and safety issues are present.

Knives are frequently used to prepare chip seeds, prepare cuttings, and during grafting. At all times, it is essential that the gardener use the knife with proper care to prevent injury. Knives must be kept in a safe location so that children may not have access to them.

Machetes and garden forks are also used to divide plants. Again, the gardener should use them with care – using suitable personal protective equipment like steel toed boots or shoes. Machetes must be stored in a safe location to prevent them being used by inexperienced people.

When digging, gardeners are advised to wear strong footwear, and while digging, to use the large muscles of the legs (not the back) to lift. Make sure you are warmed up sufficiently before starting to dig.

Some seed treatments require extra care.

• If pretreating seeds with acid, ensure appropriate safety precautions are used. Use acid only in a wellventilated location. Store and dispose of acid carefully and in an environmentally responsible way.

• Boiling water may present a hazard for scalding and burning of the skin. Care must be exercised when using boiling water – particularly around children.

• Some seeds have been coated with fungicide or pesticide treatments. After handling these seeds, make sure you wash your hands (particularly before eating, drinking or smoking).

• Many seeds are poisonous. Make sure that they are kept out of the reach of children.

The handling of rooting hormones also requires some special care. Do not breathe in the dust (in commercial operations, where exposure to these chemicals is frequent and prolonged, respirators are often used). Carefully close the containers after use, store them out of the reach of children, and wash your hands.

If dipping cuttings in fungicides, again, be careful about how these dusts and liquids are used. Store them out of the reach of children, carefully seal containers after use and wash your hands.

Misting systems present a different hazard. In a small greenhouse, a misting system may lead to slippery walkways. Be careful that these walkways do not grow algae – making another risk for slipping.

When handling all growing composts, amendments and fertilisers, avoid breathing in the dust and wash your hands before eating, drinking or smoking. Store all fertilisers out of the reach of children.


All of these precautions are common sense. Whenever possible, try to anticipate how something may cause an injury and take precautions to prevent this from occurring.

Environmentally Sustainable Practices

There are some instances where the activities of the plant propagator might have an adverse effect on a healthy environment.

Pesticides and fungicides should be used sparingly. The gardener should pay close attention to the adverse effects they may cause in the environment and balance this against the benefits they may provide.

Many compost mixtures may contain peat, and there are some questions about the sustainability of the harvesting of peat. This is covered in more detail in lesson 7. However, if you are concerned about the use of peat, then investigate the peatless alternatives available.

Seed sources are also another place where the plant propagator may have an adverse effect on the environment. Native plants and the seed from them should not be taken from the wild. It is possible to purchase seed of native plants from reputable seed houses and to propagate them in the garden. Do not purchase wild collected seed from questionable sources. Do not purchase bulbs and tubers that may have been collected from the wild.

Finally, plants may escape from the garden and cause damage to the environment the most well known of these plants may be Japanese Knotweed (Fallopia japonica, previously Polygonum cuspidatum). Gardeners whose property adjoins native woodlands must be particularly sensitive about what plants they choose to include in their gardens and what plants they choose to propagate.

Some wild plant societies may require enthusiastic gardeners to help in the propagation of wild flowers. These plants may be used to reclaim areas where the native population has been eliminated or depleted. If you are interested in plant propagation and have the interest to help reestablish wild populations of native plants, this might be an area where you could have a positive influence on the environment.


DEVELOPMENT OF A PROJECT FOLDER

Whether you are a professional looking to improve your skills at a higher level, or a keen amateur, undertaking a project can be a rewarding and enjoyable experience.

‘Why should I consider undertaking a project?’

• Working on a project of your own will give you the opportunity to do further research into an area which particularly interests you.

• This work, done alongside the course, will involve you in reading and research which will help to consolidate and underpin your course work.

• The skills you gain while researching and writing up your Project are transferable: they will stand you in good stead both as you prepare for the RHS examination (if you are working towards it) and for work you may do in the future both studywise and professionally. Communication skills, the ability to organise your thoughts, presentation skills, research and reading skills, report writing and so on are the object of training courses in many fields today.

• You will have a wellpresented piece of work of which you may be proud. It could be added to a professional portfolio and may even form the focus for a rewarding discussion at interviews. We will return to this in a moment.

Of these reasons, it is perhaps the first which is the most important. Here is an opportunity for you to focus on an area which particularly interests you, and if you so wish to have your tutor’s help and advice on it.

‘Must I undertake a project?’

No, it is entirely optional. While it would benefit you, it is not a requirement of the course or of the RHS examination.

‘I like the idea of project work, but feel daunted by the prospect.’

The two keys to all successful project work are confidence and planning.

Your confidence in your own abilities will be growing as you progress through the Lessons and receive back your tutor’s comments on your work.

You can build your confidence further by approaching the Project in stages. You need not start work on the main Project straight away. Have a look at the stages proposed overleaf:


Step One: A Diary

If you haven’t done so already, begin a Diary in which to record your gardening experiences. Do this over a period of four months or so, staying in regular contact with your tutor and submitting your Diary to him/her for comment at regular intervals.

An A4 sized hardbacked lined book (with generous 8mm line spacings) would do well. This would be durable, and photographs and press cuttings may be stuck in. It is easy enough to add some tabs for the months.

Use plenty of space. The books themselves are cheap enough to afford a couple a year if necessary. Try to record the details of operations undertaken, machines used, plant varieties, the time it took to achieve the pieces of work, rates of application, sizes of cuttings and all the treatments. Enough detail, in fact, to be able to replicate much of the activity in another year and in another place if need be.

Step Two: A miniproject

This could start at maybe your third review of the diary work. The contact between you, the tutor and the diary topic material will be working well, we hope. The mini project could be aimed to take a total of about 30 hours no more say over 6 to 8 weeks. The short but completed document would be sent to your tutor for his or her assessment and report. Hopefully this would have ironed out many of the early weaknesses which may have shown up; for example, inaccuracy of description, or failing to give references adequately.

Step Three: The Project

Your Project will involve you in between 100 and 200 study hours (between 11 and 22 full days).

The best time to begin the Project would be after your tutor’s guidance on your mini project. You will now need to:

1. Agree a topic with your tutor

By now you will have been mulling over some ideas, but if you need further help, do talk through your ideas with your tutor, or the College. We are here to help. Take note of your gut feelings: “Oh, I’d hate to work on that but I’m interested in irrigation.” These feelings are the ones to look out for because work resulting from them is more likely to be progressive and purposeful.

2. Plan your Project

You will not succeed in project writing unless you plan your work. Planning at the early stages saves time and wasted effort. It helps to focus your thoughts. You are less likely to be sidetracked while researching and writing up your work if you are following a plan. So,

a) Decide your topic.


b) Frame a title.

Here you will need to ask yourself:

Is my title focused enough? Avoid broad, general themes.

Is the scope of my enquiry realistic? Limit yourself to what you can realistically achieve in 100200 hours of work. Check that you have access to the necessary resources.

c) Write some Aims or Objectives for your Project, along the lines:

In this Project, I aim to show that:

Or

My objectives in undertaking this Project are:

While researching and writing, it will be a great help if you keep these Aims or Objectives before you at all times. They will help you to keep your focus and leave out irrelevant material. If you later include your completed Project in a Portfolio, your Aims and Objectives will impress the reader as to your organisational skills, forward planning skills, and projectwriting techniques.

d) Begin thinking about resources.

Where and when will you have access to these? Is there anything you can do now to widen the resources you already have (e.g. by joining a professional horticultural society and so gain access to a library, or by joining a local group)?

e) Produce a timetable.

This is crucial. Map out a prospective timetable, bearing in mind your other study commitments (including work on the Lessons and Assignments) and things such as holidays, time off, family commitments and so on. Space your work. Few people produce their best work under pressure, and in any case, that is not the point of undertaking the Project. This is something for you to enjoy.


Technique

Technique is allimportant in project writing. Many people approach projects with the idea that the object is simply to find out about something and record the findings. In fact, the aim is wider than this. You will need to master the language and vocabulary of your chosen theme, adopt a suitable written style, work through a logical search and review sequence, and be able to produce a summary and conclusion. Your mastery of this technique may well be useful later on. As we have noted, many projects in work environments require the ability to research a topic, collate the material and present it in a manner fit for reference by outside parties perhaps even publication.

‘Will I need to pay for my Project to be marked?’

You are very welcome to proceed independently of the College and work privately on your Project: there is no charge for work which is not submitted.

However, if you would like the guidance and input available from the College and College tutors, assuming that arrangements for the topic title and submissions are completed, the fees proposed are based on a percentage of the current fully paid up course fee rates (see overleaf). Applications for the project option may come from any of the tutored courses.


4 months’ Diary

sub missions

MINI PROJECT

sub missions

MAJOR PROJECT

sub missions

Level 1 10% 2 15% 2 25% 4

Leisure Gardening

Level 2 10% 2 20% 2 30% 4

Organic Gardening RHS Level 2 RFS Cert. Arbor. Conservation Studies Herbs for Pleasure & Profit Market Gardening

Level 3 15% 2 25% 3 40% 5

Garden Landscape & Design Drawing Garden Planting & Layout Intro to Management Garden Centre RHS Advanced RHS Diploma IoG NID in Turfculture Beyond the Basics Garden Landscape Construction Mixed Farming

Level 4 15% 2 25% 3 50% 5

M.Hort. Studies P.Dip.Arbor. Studies IoG NDT Studies

The fees relate to the time that a tutor will be expected to take in reading the work, reviewing it and reporting back to you with recommendations. The aim is that you get the best advice and maximum help that we are able to offer in support of your effort and input. The prices include return postage in the UK. Our worldwide students would be charged extra at cost.


A Project Completion Certificate will be issued with an appropriate grading.

The annual Prizes and Awards list may well include project prizewinners recommended by the tutors.

If you should decide to commence the Project study programme at enrolment or during your first course with us the fees are as per the table with the rates quoted to you.

If you decide to enrol after completing your course then the current rates would apply.

ORGANISING A PROFESSIONAL PORTFOLIO

Do you seek recognition within the horticultural world as someone with something to offer?

If so, a portfolio, beautifully presented and containing a selection (or all) of items from the list below could be invaluable. The list is not exhaustive: different individuals will have different items worth including:

a) Your qualification certificates / diplomas. b) Your written references. c) Your curriculum vitae. d) School reports if relevant. e) Your project folder. f) Associated materials like a wellkept work diary, photographs of work

achieved/past work places, etc. g) Your memberships of learned societies, RHS, Institute of Horticulture, IPPS,

NFU, etc.

The usefulness of a Portfolio at interviews

For a moment, imagine that you are an employer seeking staff (or on a smaller scale, a committee seeking an expert speaker). A preliminary selection of applicants takes place based upon a variable set of factors which may include known ability, age and experience, the way the application has been presented, references and telephone calls made. The selection by interview may then take place.

What will the interviewer look for? (What would you look for if you were conducting the interview?)

There has to be evidence of:

CAPABILITY (qualifications are in this sector) ENTHUSIASM COMMITMENT

Suppose that the interviewer has no knowledge of what your qualifications mean. He/she may never have heard of the HCC and have no idea what its Completion Certificate at Credit Grade means. (Even after 70 plus years of advertising, such is life!) If the candidate can present his/her Project Folder at this point it may be


tangible evidence of his/her capability, enthusiasm and technical mastery of the subject. This could be enough to convince the interviewer that he/she is looking at ‘just the person for the job’.

Ideally the Project should include written work, photographs, records, references concerning the theme, all carefully combined to make a neat portable folder such as a lever arch A4 file.

There you are at the interview: you look the part keen, anxious to please, healthy, very well presented, maybe very well dressed for the part, on time and enthusiastic. But then so are all the others .... or are they?

At the interview you are able to produce your Project Folder, your work references and your qualifications. This may be all the evidence required, always assuming that the interviewer is unaware of your capabilities firsthand, or from firsthand telephone calls with someone who knows of you and whose judgement is respected. Very frequently the selection will go in favour of the good candidate who is already known. Better to go for “the devil you know” than for an unknown quantity, all things being equal. People are astonishingly different in their background, outlook and motivation. A bit of known provenance takes a great deal of beating.

Back to the interview: you will have handed over the file and the interviewer is interested enough to ask a question or two. Will you be floored or could you answer? There may be superb work cribbed from elsewhere, and it may only take one question to unearth this weakness; so do your own work and quote your references for the work of others.

WE HOPE THAT YOUR PROJECT FOLDER WILL BACK UP YOUR HCC COURSE COMPLETION CERTIFICATE A DISTINCTION CERTIFICATE AND A DEMONSTRABLY DISTINCTIONLEVEL PROJECT FOLDER.


BIBLIOGRAPHY AND FURTHER READING LIST

181 Propagation from cuttings Jim Gardiner RHS Wisley handbooks 182 Propagation from seed Jim Gardiner RHS Wisley handbooks 206 Plant Propagation P D A McMillan

Browse RHS Wisley handbooks

Auriculas G. Baker & P. Ward Batsford Container Plant Manual Edmonds J Grower Books 1980 Growing Media Manual N Bragg Grower Books Hardy Woody Plants from Seeds Philip McMillan

Browse Grower Books

Nursery Practice Aldhous, J R HMSO Forestry Commission 1972

Nursery Stock Manual Lamb, Kelly & Bowbrick

Grower Books

Plant Propagation Philip McMillan Browse

Mitchell Beazly

Plant Propagation Principles and Practices

Hartmann & Kester Prentice Hall

Plant Propagation: Insight, Fundamentals and Techniques

Oliver N. Menhinick et al.

HCC Publishing

Practical Woody Plant Propagation for Nursery Growers

Macdonald B Batsford 1987

Principles of Horticulture Adams, Bamford, Early

Butterworth: Heinmann

Propagation of Hardy Perennials Bird R Batsford 1993 The Grafters Handbook Garner R.J Cassell The Hardy Nursery Stock Technical manual

Lothian and Edinburgh Enterprise Limited

Belwood Nurseries Ltd.

The New RHS Dictionary of Gardening

RHS RHS

Tree Nurseries Liebsher, K BCTV 1984 Seed Germination: Theory and Practice

Deno, Norman C. Selfpublished by Dr. Deno

Documents

Propagation Sample Lesson