Growing Media Soilless Media, Is it dirt? That is the question

Growing Medium The health and quality of floriculture crops rest largely with the growing medium GROWING MEDIUMGROWING MEDIUM is the material in which plants are grown –In field production or a home garden, soil is the medium. –In greenhouse production, a variety of materials are used as growing media. Usually soil is not used in the greenhouse.

Why is Growing Media So 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 Media 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 Media Organic Matter Bulk Density Porosity Aeration Water Holding Ability pH Cat ion Exchange Capacity

Organic Matter Decayed or partially decayed remains of plants and animals –It should remain stable and not break down before the crop is finished –Peat moss and bark are the most common sources of organic matter in growing medium

Bulk Density The ratio of the mass of dry solids in a medium to the volume of the medium –Light bulk density eases handling and shipping of potted plants –High or heavy bulk density is needed to provide support for plants Easter lilies need a medium with a high bulk density

Porosity The spaces between the solid particles of a growing medium are pores POROSITYThe higher percentage of pores or POROSITY in a medium results in better water drainage and aeration, or the exchange of gases –Good mineral or garden soils have about 50% pore space –Organic media used in greenhouses have between 75 and 85% pore spaces

Aeration 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 convert sugars to energy –This chemical process is known as respiration –A byproduct of respiration is carbon dioxide –It is important that a medium has sufficient pore spaces to allow an exchange of carbon dioxide and oxygen

Water-Holding Ability A growing medium must store water that is available for plant use AVAILABLE WATERAVAILABLE WATER is water that can be absorbed by the plant roots Available water is found in the pore spaces of the medium UNAVAILABLE WATERSome water in the medium is considered 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

pH pHThe acidity or alkalinity of the medium is measured as pH A 14-point scale is used to measure pH –Neutral is 7.0 – is Acid – is alkaline or basic

pH 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+ and 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 Capacity The measure of a medium’s capacity to hold nutrients –Many nutrients are positively charged cations, such as potassium (K + ), Calcium (Ca +2 ), Magnesium (Mg + ), Copper (Cu + ), Iron (Fe +3 ), Manganese (Mn +2 ), and Zinc (Zn +2 )

Cation 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 CATION EXCHANGE CAPACITY

Growing Medium Components What’s In That stuff?

Soilless 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 disease, insect, and weed problems –Nutrients are added and pH is adjusted for optimal plant growth Soilless mixes can be purchased pre- mixed or you can mix your own

Common Components of a Soilless Mix Peat moss Coir Vermiculite Perlite Bark Sand Plastic foam Calcined clay Rock wool Mineral soil

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

A common ingredient in growing media Origin is a mineral called mica –Mica is heated to 1800 o 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

Originates from volcanic rock –It is crushed, then quickly heated to about 1800 o 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

Human made material from an igneous rock, basalt Heated to temperatures of 2700 o 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