Image source: Reed, D.

1996. Water, Media, and

Nutrition for Greenhouse

Crops. Ball Publishing.

Batavia, Illinois.

Root SubstratesRoot Substrates

Three Basic Types of Three Basic Types of Root Systems:Root Systems:

FibrousFibrous TaprootTaprootStorageStorageTaprootTaproot

Source: Raven, Evert, and Eichhorn. 1986. Biology of Plants. 4th Ed. Worth Publishers, Inc.

Smith. 2000.The Vegetable Gardener’s Bible. Storey Books. Pownal, VT.

Root FunctionsRoot Functions

Anchoring the plant (citrus tap root)Anchoring the plant (citrus tap root)

Absorbing water and minerals from the soil Absorbing water and minerals from the soil and transporting them to the stemand transporting them to the stem

Food Storage (Carrot)Food Storage (Carrot)

Aeration (Black Mangrove and Cypress; Aeration (Black Mangrove and Cypress; pneumatophores)pneumatophores)

Support (Red Mangrove and Corn; Support (Red Mangrove and Corn; Proproots)Proproots)

Root Systems Consist of:Root Systems Consist of: Primary RootsPrimary Roots

Secondary RootsSecondary Roots

Root HairsRoot HairsLink to website

Image Source: Capon. 1990. Botany for Gardener’s. An Introduction and Guide. Timber Press. Portland, OR.

Root HairsRoot Hairs

Root hairs are tubular Root hairs are tubular extensions of epidermal extensions of epidermal cells cells

Increase root surface area Increase root surface area Greatly increases plants Greatly increases plants

ability to absorb water and ability to absorb water and minerals from the soilminerals from the soil

Image Source: Capon. 1990. Botany for Gardener’s. An Introduction and Guide. Timber Press. Portland, OR.

Link to Website

Link to WebsiteLink to Website

Root Substrate FunctionsRoot Substrate Functions

Reservoir for plant nutrients Reservoir for plant nutrients

Hold plant available waterHold plant available water

Provide means for gas exchangeProvide means for gas exchange

Provide anchorage for the plantProvide anchorage for the plant

Use of Field Soil in GHUse of Field Soil in GH Used where plants are produced in in-Used where plants are produced in in-

ground beds (some cut flowers, some ground beds (some cut flowers, some greenhouse tomatoes) –issues with greenhouse tomatoes) –issues with disease build-updisease build-up

Many greenhouses are located in areas Many greenhouses are located in areas without a good supply of field soil for without a good supply of field soil for potted plants (even if available – potted plants (even if available – environmentally unsound)environmentally unsound)

This lecture will focus mostly on soilless This lecture will focus mostly on soilless media for the greenhouse production of media for the greenhouse production of bedding plants and ornamentalsbedding plants and ornamentals

Root Substrate PropertiesRoot Substrate Properties

Stability of Organic MatterStability of Organic Matter

Carbon-to-Nitrogen RatioCarbon-to-Nitrogen Ratio

Bulk DensityBulk Density

Moisture Retention and Aeration Moisture Retention and Aeration

Cation Exchange Capacity Cation Exchange Capacity

pHpH

Organic Matter StabilityOrganic Matter Stability

You want minimal decomposition of You want minimal decomposition of organic matter during the production cycle organic matter during the production cycle

Decomposition reduces substrate volume Decomposition reduces substrate volume and produces finer texture – reducing and produces finer texture – reducing water holding capacity and aeration water holding capacity and aeration simultaneously simultaneously

Exceptions: in ground vegetable and Exceptions: in ground vegetable and flower production – in this case organic flower production – in this case organic matter breakdown is acceptable – organic matter breakdown is acceptable – organic matter is replenished on an annual basis matter is replenished on an annual basis

C:N RatioC:N Ratio You must take this ratio into consideration when You must take this ratio into consideration when

managing organic matter managing organic matter C:N ratio should be 30:1 or less – when more C:N ratio should be 30:1 or less – when more

carbon is present microorganisms will use the carbon is present microorganisms will use the nitrogen from fertilizer nitrogen from fertilizer

Microorganisms that break down the organic Microorganisms that break down the organic matter and ultimately make nutrients available matter and ultimately make nutrients available for plant growth require N for protein for plant growth require N for protein

Initially they may actually tie up nearly all the Initially they may actually tie up nearly all the nitrogen during the decomposition process. C:N nitrogen during the decomposition process. C:N ratio for sawdust is 1000:1 ratio for sawdust is 1000:1

Warmer temperatures accelerate the Warmer temperatures accelerate the decomposition process.decomposition process.

Bulk DensityBulk Density

Bulk density important for Bulk density important for containerized crops containerized crops

If a media is too light pots may If a media is too light pots may topple when the media begins to dry topple when the media begins to dry outout

Benefits of heavier root substrate Benefits of heavier root substrate choices must be balanced with the choices must be balanced with the additional costs of handling and additional costs of handling and shipping shipping

Moisture Retention and AerationMoisture Retention and Aeration

3 components of a substrate3 components of a substrate

– Solid particlesSolid particles

– Liquid water coating particle surfaceLiquid water coating particle surface

– Pore spacePore space

After watering 10-20 percent of After watering 10-20 percent of the volume of the Root substrate the volume of the Root substrate should be occupied by airshould be occupied by air

Desirable Root Substrate PropertiesDesirable Root Substrate Properties

Any organic matter should be stableAny organic matter should be stable

C:N ratio of at least 30:1 (less better)C:N ratio of at least 30:1 (less better)

Bulk Density: 40-60 lbs/ftBulk Density: 40-60 lbs/ft33

At CC 10-20% of root substrate volume At CC 10-20% of root substrate volume should be airshould be air

CEC 6-15 me/100 cc is acceptableCEC 6-15 me/100 cc is acceptable

pH – for most crops 6.2-6.8pH – for most crops 6.2-6.8

Other Issues for ConsiderationOther Issues for Consideration

Water Content vs. Container HeightWater Content vs. Container Height

Container SizeContainer Size

History of MixesHistory of Mixes

Most soilless mixes used today are derived Most soilless mixes used today are derived from two research programsfrom two research programs

– Dr. Baker from the University of California (5 Dr. Baker from the University of California (5 mixes and 6 base fertilizers; 30 combinations)mixes and 6 base fertilizers; 30 combinations)

– Dr. Boodley and Sheldrake at Cornell (most Dr. Boodley and Sheldrake at Cornell (most popular) – nutritional additives based on croppopular) – nutritional additives based on crop

Overall most common is 50% peat, 25% Overall most common is 50% peat, 25% vermiculite, and 25% perlitevermiculite, and 25% perlite

FAFARD® MIX #2. For germination mixture, packs and pots up to 10 inches. Canadian Sphagnum Peat Moss, Horticultural Vermiculite, Horticultural Perlite. Bag Size: 2.8 cu. ft. Wt. 9 to 12 lbs. per cu. ft.

FAFARD® MIX #3. For 4-inch and larger; pots and baskets. Canadian Sphagnum Peat Moss, Horticultural Vermiculite, Horticultural Perlite, Aged Pine Bark. Bag Size: 2.8 cu. ft. Wt. 14 to 17 lbs. per cu. ft.

FAFARD® MIX #3B. Suitable for a wide range of crops, from seedlings to packs to baskets. Canadian Sphagnum Peat Moss, aged Pine Bark, Vermiculite and Perlite. More peat and less bark than #3. Bag Size: 2.8 cu. ft. Wt. 12 to 15 lbs. per cu. ft.

FAFARD® MIX #3S. An economical soilless mix for packs, pots and baskets composed of Canadian Sphagnum Peat Moss, Vermiculite, Aged Pine Bark, Polystyrene Beads. Bag Size: 2.8 cu. ft. Wt. 12 to 15 lbs. per cu. ft.

FAFARD® MIX #4. A finer textured mix with greater water-holding capacity than 3B, for pots and baskets. Excellent for drip or subirrigation. Contains Canadian Sphagnum Peat Moss, Aged Pine Bark and Vermiculite. Bag Size: 2.8 cu. ft. Wt. 12 to 15 lbs. per cu. ft.

Growing Mix No. 2. A versatile soilless mix composed of Canadian Sphagnum Peat Moss, Vermiculite and Perlite, plus starter nutrients and wetting agent. Ready to use direct from the bale—no mixing or sterilizing! We recommend it highly for growers as a time- and money-saver. 3.8 cubic feet compressed bale.

H6658-9—1-49 bales, $21.00/bale; 50-100 bales, $19.25/bale

Growing Mix No. 1P. This economical peat-based growing mix contains 2 main ingredients: Canadian Sphagnum Peat Moss and Perlite. It meets Fafard®’s high quality standards, pH adjusted, and contains starter nutrients and wetting agent, but by not adding vermiculite; passing savings along to you! 3.8 cubic feet compressed bale.

H6732-7—1-49 bales, $19.85/bale; 50-100 bales, $18.25/bale

METRO-MIX 366-P W/SCOTTS COIR

Mix contains 30-40% processed coconut coir pith along with medium grade vermiculite, composted pine bark and hort perlite. Includes starter nutrient charge and wetting agent. Ideal for potted plants, bedding and hanging basket production. 5.2-6.4 Ph range after wet-out. Weight approx. 48 lbs.

METRO-MIX 380

A blend of composted pine bark, medium grade vermiculite, Canadian sphagnum peat moss and hort. perlite, combined with a starter nutrient charge and wetting agent. A moderately coarse mix ideal for potted and bedding plants, landscape applications and garden mums or stock plants. Ph range of 5.0-6.5 after wet-out. Weight approx. 45 lbs.

METRO-MIX 510

This mix contains sphagnum peat, vermiculite, composted pine bark, processed bark ash, wetting agent and nutrient charge. It has a coarser texture and is useful for long-term growing-on of hanging baskets, potted plants, nursery container plants and interiorscapes. pH range after wetting is 5.3-6.7. Weight approx. 56 lbs.

METRO-MIX 700

An excellent coarse mix with outstanding aeration, percolation and nutrient retention characteristics. A blend of Canadian Sphagnum peat moss, vermiculite, perlite, moderately coarse composted pine bark, wetting agent and nutrient charge. pH range is 5.3-6.5 after wetting with acid forming fertilizers. Weight approx. 57 lbs.