Horticulture Principles and Practices

Cost
146 Chapter 4 Plant Growth Environment
Materials vary in cost. Inorganic components can be especially expensive. Substitutes can
be made, as previously indicated, if one understands the role of ingredients in the mix.
Use
The mix prepared should meet the needs of the operation in terms of plant requirements and
any automation available. Certain mixes are not conducive for use in potting machines.
Ease of Preparation
Pasteurization is critical to the formulation of mixes. Certain ingredients are difficult to
pasteurize. If chemicals (i.e., fertilizers) are to be added, care should be taken to avoid
hazards from incorrect calculations and mixing.
4.10.3 CONSTITUTING MIXES
All of the ingredients previously described do not have to be included in each mix. Mixes
are formulated for specific purposes, based on the needs of the plant. Certain mixes have
broad application. Examples of such mixes are
1. 1:1 of sphagnum moss and vermiculite
2. 1:1:1 of sand, sphagnum moss, and a wood product (e.g., bark or wood
shavings)
3. 3:1:1 of peat, perlite, and vermiculite
4. 2:1:1 of peat, bark, and sand
5. 2:1:1 of peat, perlite, and vermiculite
6. 2:1 of peat and perlite
The appropriate amounts of lime and fertilizer should be added to these mixes. These ingredients
are included in these proportions on the basis of volume rather than weight,
since they all vary in bulk density. It is important that the mix be disease free; therefore,
commercial products are often sterilized by either heat (steam) pasteurization or chemical
treatment (e.g., methyl bromide).
Standard Mixes
Certain growing mixes have been developed and popularized over the years. These
media form the standard, which may be modified for specific purposes. The advantages
of these standard mixes include first the fact that they have been thoroughly researched
and proven to be successful and second that using standard mixes removes the guesswork
from the formulation of mixes. They can be reproduced and thus are useful in quantitative
studies where uniformity of research materials is needed. These standard mixes are
predictable in their effects. Two of the commonly utilized standard mixes are described
in Table 4–11. Soil mixing can be done on a large scale using commercial-batch soil mixers
or continuous media mixing systems.
Roles of Ingredients in a Mix
Each soilless mix ingredient has a specific role to play in the mix. The property of a mix
and the ingredient responsible are as follows:
1. Good water retention. Soilless mixes are utilized mainly in plants cultured in
containers. The volume of soil is usually limited. The mix materials should be able
to retain moisture so that the medium does not dry out too quickly. Organic
materials are used as ingredients for increasing the water retention of the medium.