Growing media _______________________________
The first article I ever wrote for the NZ Commercial Grower (the predecessor of the NZGrower) was published nearly 60 years ago.
This was written as a raw (very raw) extension officer when I was initially based in Oamaru in 1958. At that time there was a buoyant greenhouse tomato industry based around Oamaru (mainly at Kakanui), as production in New Zealand was very much based on local, rather than imported (from the North Island) produce. However the North Otago tomato growers had one major problem. The predominant soil type was the so called “tar” soils developed from an undersea volcano many centuries earlier. Excellent for growing outdoor vegetables, but extremely difficult to fumigate using methyl bromide or chloropicrin, as the gases remained locked up in the soil.
For this reason the greenhouse soils were either steam sterilized or resoiled between crops. Steaming was very expensive (but a safe strategy) while replacing the greenhouse soil (to a depth of 30 cm) was a risk, in that it was quite possible to bring in diseases or pests with the new soil, and in any case although the yields from the new soil were higher than normal, the quality of the fruit tended to be lower due to the lower fertilizer (particularly potassium) levels.
Another alternative strategy, involving much less soil movement, was to fill up old kerosene tins with new soil, and put these on the glasshouse floor, thus not only moving far less soil, but also ensuring in the cold North Otago winters, that the root zone was kept much warmer than by planting directly in the greenhouse soil. The idea of using an improved soil to fill the kerosene tins was at that time considered much too expensive.
We have come a long way since then. Rock wool slabs imported all the way from Europe, or coir modules produced in Sri Lanka or India have become the norm for the majority of greenhouse crop producers, and the rewards of using a high quality standard growing medium have become apparent.
Several years ago I attended a conference on growing media in Barcelona, Spain at which it was stated that there was going to be a world shortage of the basic raw materials which make up good horticultural growing media. The prime organic component of growing media have in the past been peat, which is now under pressure from environmentalist. The problem is that although there is plenty of peat in the world (in fact it is apparently being replaced at a faster rate than it is being used) this replacement is occurring in difficult of harvest (mine) places such a northern Canada/Finland etc, and the easy to harvest places are being overharvested.
The concern about future sources of organic matter was so serious that consideration is being given to growing trees, simply to provide a stable, reliable long term source of organic potting medium.
New Zealand is very fortunate in that we have a ready made source of organic potting media in the bark from the pine trees harvested for sale as timber, and have developed a very acceptable method of treating this Pinus radiata bark for use as a growing medium.
Ungraded, unprocessed pine bark. New Zealand’s growing medium for the future?