The first recorded use of soil mixes in containers was that of the Egyptians in the period around 2000 BC. They used containers to transport frankincense trees from the Somali Coast to Egypt. Development since then had been slow and uncoordinated, until the 1950s, when significant advances were made.

It was during this period that English and American interests began to develop a soil mix that would reliably assist the containerised horticulture industry.

Although it is not always evident, there are many advantages in the use of a clean, well-structured and chemically-balanced soil medium. If you decide to grow container plants in soil dug from your backyard, you may very well succeed in many instances. You may not, however, be able to reliably grow thrifty plants. Many traps await the unwary in this field, for wet tropics soil often acts adversely when in containers.

Some assumptions concerning the compatibility of certain plants to various soil mixes have been derived from 'old wives' tales'. In some cases they are based on the idea that the ideal soil for a plant is one identical to that of its native habitat. In other instances, many other factors apart from soil conditions have been overlooked in the assessment of reason for a plant's successful growth.

A general soil mix has now been developed to cater for most plants grown in the tropics. African Violets and Cactii etc., still require specialised soil mixes.

There are four essential characteristics of good container soil medium.

1. It should possess a structure that permits the entry of air and be able to hold moisture while permitting excess to drain away.

2. It should be able to provide an adequate and balanced nutrient supply at every stage of plant growth (with supplements).

3. It should be free of harmful organisms and plant toxins.

4. The constituents should be readily available, for uniformity of replication.

As a recommendation following the above principles these ingredients may be combined to produce a soil mix suitable for most tropical plants.

2 parts coarse sand
3 parts loam soil
2 parts peat moss

The availability of these ingredients is not always good, so substitutes may be used.

The 'loamy' characteristic of the loam soil ingredient is not critical, for peat moss can provide adequate organic matter under most circumstances.

If one wishes to grow seedlings or rooted cuttings, the sand constituent may be doubled, to provide better drainage.

Various substitutes may be added to the basic mix, such as vermiculite, perlite, sawdust (from untreated timber only) or peanut shells.

If peanut shells or sawdust are substituted, an increase in soil nitrogen is needed. The decomposition of these materials needs a lot of nitrogen, which can induce a deficiency in the growing plant.

In general, fertilizers should be used sparingly. The loam soil ingredient will usually supply most of the trace element requirements, so a controlled-release granular fertilizer is often adequate. It may be added during the mixing process, or after plant establishment in the new soil mix.

To complement the time spent in preparation of a soil mix, one should keep hygiene in mind. Prevention is still better than cure in the case of nursery hygiene, for the control of pathogens can be difficult if not impossible, after infection.

Nursery hygiene means:

1. Sterilizing soil, pots and implements.

2. Isolating sterilized soil from possible sources of infection.

3. The use of clean plant material.

There are many ways in which infection can occur. Fungi and bacteria may be splashed into pots with considerable ease, and may even be carried on the end of a watering hose, dirty hands or gloves.

Some plant propagators do not integrate the elements of soil preparation and nursery hygiene. This often results in disappointing growth in plants that should be thriving. One of the problems associated with nursery hygiene is the insidious nature of most pathogens. They are invariably invisible to the naked eye, yet are capable of debilitating effects on plants. Unlike many human diseases, there are few control measures available that are completely effective on bacterial and fungi disorders.

The cost of control measures is sufficient reason in itself to take care with the plants you grow.

Article from Ingham Branch Newsletter, Feb.1989

DATE: May 1989

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