Growing Growing MediaMedia

Soilless Media, Is it Soilless Media, Is it dirt? dirt?

That is the questionThat is the question

Growing MediumGrowing Medium• The health and quality of floriculture crops

rest largely with the growing medium

• GROWING MEDIUM GROWING MEDIUM is the material in which plants are grown– In field production or a home garden, soil is In field production or a home garden, soil is

the medium.the medium.– In greenhouse production, a variety of In greenhouse production, a variety of

materials are used as growing media.materials are used as growing media.• Usually soil is not used in the greenhouse.

Why is Growing Media So Why is Growing Media So Important?Important?

• Growing medium holds water for plant use

• Growing medium provides nutrients for the plant

• Growing medium permits the exchange of gases to and from the plant roots

• Growing medium provides support for the plant

Greenhouse Growing Greenhouse Growing Media is DifferentMedia is Different

• Soil that is taken from outside and placed in a pot inside becomes very hard and undesirable for plant growth.

• Greenhouses depend upon the media to provide uniform growth in plants.

• Greenhouse media is light and easy to ship whereas soil is heavy and would increase the cost of shipping.

Desirable Properties of MediaDesirable Properties of Media

• Organic Matter

• Bulk Density

• Porosity

• Aeration

• Water Holding Ability

• pH

• Cat ion Exchange Capacity

Organic MatterOrganic Matter• Decayed or partially decayed remains of

plants and animals – It should remain stable and not break down It should remain stable and not break down

before the crop is finishedbefore the crop is finished– Peat moss and bark are the most common Peat moss and bark are the most common

sources of organic matter in growing mediumsources of organic matter in growing medium

Bulk DensityBulk Density• The ratio of the mass of dry solids in a

medium to the volume of the medium– Light bulk density eases handling and Light bulk density eases handling and

shipping of potted plantsshipping of potted plants– High or heavy bulk density is needed to High or heavy bulk density is needed to

provide support for plantsprovide support for plants• Easter lilies need a medium with a high bulk

density

PorosityPorosity• The spaces between the solid particles of

a growing medium are pores• The higher percentage of pores or

POROSITYPOROSITY in a medium results in better water drainage and aeration, or the exchange of gases– Good mineral or garden soils have about 50% Good mineral or garden soils have about 50%

pore spacepore space– Organic media used in greenhouses have Organic media used in greenhouses have

between 75 and 85% pore spacesbetween 75 and 85% pore spaces

AerationAeration• The exchange of gases in the medium• Pore spaces that allow air pockets within the

medium are vital for healthy root growth– Root cells use oxygen from the pore spaces to Root cells use oxygen from the pore spaces to

convert sugars to energyconvert sugars to energy– This chemical process is known as respirationThis chemical process is known as respiration– A byproduct of respiration is carbon dioxideA byproduct of respiration is carbon dioxide– It is important that a medium has sufficient pore It is important that a medium has sufficient pore

spaces to allow an exchange of carbon dioxide spaces to allow an exchange of carbon dioxide and oxygenand oxygen

Water-Holding AbilityWater-Holding Ability• A growing medium must store water that is

available for plant use• AVAILABLE WATER AVAILABLE WATER is water that can be

absorbed by the plant roots• Available water is found in the pore spaces of

the medium• Some water in the medium is considered

UNAVAILABLE WATER UNAVAILABLE WATER because it is a thin film of water that binds so tightly on the media particles that it cannot be used by the plant

pHpH• The acidity or alkalinity of the medium is

measured as pHpH

• A 14-point scale is used to measure pH

– Neutral is 7.0Neutral is 7.0

– 0- 7.0 is Acid0- 7.0 is Acid

– 7.0-14.0 is alkaline or basic7.0-14.0 is alkaline or basic

pHpH• The pH is determined by the concentration of

hydrogen (H+) ions and hydroxyl (OH-) in the soil solution– A sample of pure water has an equal number of H+ A sample of pure water has an equal number of H+

and OH- ions and is therefore neutraland OH- ions and is therefore neutral

• Most essential elements for plant growth are available to most plants when the pH of the soil is between 5.5 and 7.0

• Most plants grow best when the soil pH is between 6.0 and 7.0

Cation Exchange CapacityCation Exchange Capacity

• The measure of a medium’s capacity to hold nutrients– Many nutrients are positively charged cations, Many nutrients are positively charged cations,

such as potassium (Ksuch as potassium (K++), Calcium (Ca), Calcium (Ca+2+2), ), Magnesium (MgMagnesium (Mg++), Copper (Cu), Copper (Cu++), Iron (Fe), Iron (Fe+3+3), ), Manganese (MnManganese (Mn+2+2), and Zinc (Zn), and Zinc (Zn+2+2))

Cation Exchange CapacityCation Exchange Capacity

• Particles in the medium have negative charged sites

• The cations are attracted to these negatively charged sites on medium particles

• Cations have the ability to leave a medium particle and be replaced by another cation– This ability to exchange cations is called This ability to exchange cations is called

CATION EXCHANGE CAPACITYCATION EXCHANGE CAPACITY

Growing Medium Growing Medium ComponentsComponents

What’s In That stuff?What’s In That stuff?

Soilless MixesSoilless Mixes• Most greenhouses today use uniform

soilless mixes that are composed of mostly peat moss or bark with perlite and/or vermiculite– Basic components are sterilized to eliminate Basic components are sterilized to eliminate

disease, insect, and weed problemsdisease, insect, and weed problems– Nutrients are added and pH is adjusted for Nutrients are added and pH is adjusted for

optimal plant growthoptimal plant growth

• Soilless mixes can be purchased pre-mixed or you can mix your own

Common Components of a Common Components of a Soilless MixSoilless Mix

• Peat moss• Coir• Vermiculite• Perlite• Bark• Sand• Plastic foam• Calcined clay• Rock wool• Mineral soil

Peat Moss

Peat Moss

• An organic material dug from peat bogs– Canada, and to a lesser extent, Michigan and Florida

are sources of peat for growers in the United States– Canadian peat if very uniform and of high quality

• Peat moss has light bulk density, good moisture-holding ability, good air space qualities for the exchange of gases, adequate cation exchange capacity, and a stable pH that is usually between 3.5 and 4.5

COIR

Coir

• Made from waste products of the coconut industry and is therefore considered a renewable resource

• Has similar characteristics to peat moss– High water-holding capacity and excellent

drainage– Encourages faster rooting of plants– Disadvantage is high salt content because

coconuts grow near the sea

Vermiculite

Vermiculite

• A common ingredient in growing media• Origin is a mineral called mica

– Mica is heated to 1800o F, which causes it to expand like an accordion

– Spaces made by the expansion result in good water-holding ability and aeration

– It is very light-weight and can be easily compressed

– Has a good cation exchange capacity– Neutral to slightly alkaline pH

Perlite

Perlite

• Originates from volcanic rock– It is crushed, then quickly heated to about

1800o F. The heat causes it to pop like popcorn to form a lightweight aggregate

– A good substitute for sand– Stable, sterile, has little cation exchange

capacity, has a pH of 7.5 and provides good aeration and drainage

• Contains fluoride, which can cause leaf damage to some monocots

BARK

Bark

• From trees• Obtained as a byproduct through the

timber industry• Relatively inexpensive• The most widely used is pine• Provides moisture holding ability and

aeration• Bark is best next to peat moss as an

organic medium

PLASTIC BEADS

Plastic Foam

• Flakes or beads– Styrofoam is the most common

• Synthetic polystyrene material• Lightweight and stable• Provides good drainage and aeration• Lacks cation exchange capacity, water holding

ability• Neutral pH• Tends to float to the surface of growing media

Calcined Clay

Calcined clay

• Clay aggregate heated to form a hard, stable particle

• High bulk density

• Improves water drainage and aeration

• Has some cation exchange capacity

Rock Wool

Rock Wool

• Human made material from an igneous rock, basalt• Heated to temperatures of 2700o F and once liquefied, is

spun into fibers similar in appearance to cotton candy• Used extensively in hydroponics operation• Cubes are used in plant propagation• Granular forms of rock wool are used as a medium

component• Good water holding capacity and good aeration• Slightly alkaline• Low cation exchange capacity

Sand

• Found naturally as a result of weathering rock• Heavy and has a high bulk density that provides

solid support for larger plants• Improves drainage and aeration when used with

soil– Can actually reduce aeration in peat or bark by filling

in pore spaces

• pH is between 7.5 and 8.5• Must be sterilized to destroy disease organisms

SOIL

Mineral Soil

• Obtained from nature as a result of weathered rock

• Difficult to find uniform mineral soil with a favorable pH and good structure and texture