MEDIUM ADDITIVES

Video  Choosing a soil mix – a quick intro so a few of the ideas behind using a medium in a greenhouse Choosing a soil mix

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 Mixtures Volume/Volume RatioComponents 2:1Peat, Perlite 2:1:1Peat, Perlite, Vermiculite 3:1:1Peat, Perlite, Vermiculite 2:1:1Peat, Bark, Perlite