Horticulture Principles and Practices

Cultivation
Cultivation is a tillage operation performed as needed during the crop production
cycle, anytime between seed germination and crop harvest. The primary goal of
cultivation is to control weeds. However, soil is also cultivated to improve infiltration
and aeration.
4.10 POTTING MEDIA
Soils, as they occur in nature, consist of mineral elements. They are dense and bulky.
Plants are not always grown outdoors in fields. Some are grown indoors and require containers
to hold the soil. Because of the bulky nature of natural soil, scientists have
developed methods for synthesizing growing media for a variety of purposes. The ingredients
in such mixes may be natural or artificial. The goal of such creations is to use
proportions of these ingredients in mixes such that the results mimic the environment
that a natural soil would provide for a seed or plant. In fact, since humans are in control,
they are able to manipulate the proportions of ingredients to create a wide variety of
growing conditions not available in nature. These mixes are sometimes called soilless
mixes because they consist of materials that are not true soil ingredients. However, certain
mixes contain real or true soil material.
4.10.1 FORMULATING A MIX
Properties of a Good Mix
Potting mixes are formulated according to need. Certain mixes are constituted for germination
and others for growth. Various plants prefer various characteristics in mixtures.
Difference notwithstanding, all mixtures should have certain basic physical, chemical,
and biological properties.
1. Physically, the mix should drain freely (good infiltration) and be well aerated.
2. The materials used should have high particle stability (i.e., it should not
decompose rapidly) and be easily wetted.
3. It should have good moisture-holding capacity and good bulk density.
4. For use in automated pot-filling machines, the mix should flow easily.
5. Chemically, the material used should not produce any toxins. For example,
sawdust or chipping from treated lumber should be washed before use.
Natural toxins in plants usually break down when plant materials decompose
properly.
6. The mix should have good CEC (about 50 to 100 mEq/100 g of soil) and buffer
capacity. The pH should be about 5.5 to 6.0 or according to the need of the plant
to be grown.
7. Nutrient element needs for proper growth and development should be
provided in a balanced amount. Certain mixes include special fertilizer
conditioners.
8. Artificial soil mixes are usually pasteurized to kill pathogens. However, beneficial
microbes should be present in the soil.
Materials
Materials used in formulating a mix include those of organic and inorganic origin
(Figure 4–20.)
142 Chapter 4 Plant Growth Environment