MEDIUM ADDITIVES

Video Choosing a soil mix – a quick intro so a

few of the ideas behind using a medium in a greenhouse

Review There are many things to take into

consideration when choosing a soil for your plants Aeration Bulk Density

Pore Spaces Porosity Water Holding Ability

CEC Organic Mater

pH

Peat and Peat-Like Materials Peat moss is formed by the accumulation

of plant materials in poorly drained areas Sphagnum Moss is the most desirable

from of organic matter for the preparation of growing media. Drainage and aeration are improved in

heavier soils while moisture and nutrient retention are increased in lighter soils.

Wood Residues These materials cause nitrogen

depletion by soil microorganisms during the decomposition process. Leaf Mold – can improve the aeration,

drainage, and water holding properties of a growing media (also it is readily available at low costs).

Barks – a byproduct of the pulp, paper, and plywood industries, this product produces physical properties similar to those of sphagnum moss.

Rice Hulls A by product of the rice milling industry,

they are extremely effective at improving drainage. Unlike other media additives N depletion is not a serious problem found with rice hulls.

Perlite A silicous mineral of volcanic origin. Its

lightness and uniformity make perlite very useful for increasing aeration and drainage.

Vermiculite A mineral with plate like particles which

have a very high water holding capacity and aid in aeration and drainage. It also has excellent exchange and buffering capacities as well as the ability to supply potassium and magnesium.

Because of these chemical and physical properties it is very desirable for container media.

Calcined Clays Have a relatively high CEC as well as

water holing capacity. It is also a very durable additive which makes it a great amendment to growing medias.

Preparing Soilless Growing Media Although amendment combinations may

vary, basic objectives in the preparation of a growing media are alike. An effective program should produce a growing media that is:

(Continued on next slide)

Preparing Soilless Growing Media Porous and well drained, yet retentive of sufficient moisture

to meet the water requirements of plants between irrigations; Relatively low in soluble salts, but with an adequate exchange

capacity to retain and supply the elements necessary for plant growth;

Standardized and uniform with each batch to permit the use of standardized fertilization and irrigation programs for each successive crop;

Free from harmful soil pests; pathogenic organisms, soil insects, nematodes and weed seeds

Biologically and chemically stable following pasteurization; primarily free from organic matter that releases ammonia when it is subjected to heat or chemical treatments.

Commonly Used Soilless MixturesVolume/Volume Ratio Components

2:1 Peat, Perlite

2:1:1 Peat, Perlite, Vermiculite

3:1:1 Peat, Perlite, Vermiculite

2:1:1 Peat, Bark, Perlite