Mother's Mini-Manual: Greenhouse Gardening

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C0 2

SUPPLY Many studies have shown that plants grown in a C0 2-enriched atmosphere are larger and more luxuriant than those grown in a non-enriched environment. And plants raised in an "ordinary" atmosphere do better than those raised in a C0 2-poor environment.

If you have a sunken or an airtight greenhouse, then, you might want to improve its growing conditions by somehow increasing the CO 2 in the unit's atmosphere, especially on bright, sunny days during the lengthy cold spells when the greenhouse is tightly sealed.

The most common sources of C0 2 for the small greenhouse owner are dry ice (just let it melt on the walks), compressed gas in cylinders (control its flow with a valve, meter and pressure regulator), and alcohol (the cheapest source, burn it in a kerosene lantern).

If you find the above sources of C0 2 a bit complicated, bothersome or expensive, you might try a variation of Jim DeKorne's system. By raising rabbits which inhale oxygen and exhale C0 2 in cages under his hydroponic tanks, the experimenter/author of The Survival Greenhouse managed to increase the C0 2 level in his greenhouse to an estimated 700 to 800 parts per million (300 ppm is the usual concentration in the atmosphere) and at the same time obtained valuable manure for his composting bin!

PHOTOPERIOD

The beginning greenhouse gardener should realize that just as deciduous trees enter dormant states as the days grow shorter, certain other plants will not flower and produce fruit year round. Not even if he or she keeps the enclosed environment warm in the winter (unless he or she finds some way to supplement the natural light those plants receive).

In The Survival Greenhouse, Jim DeKorne suggests that fluorescent tubes — which produce both the red and blue wavelengths beneficial to plants — can be used as artificial sources of light in a hothouse. These energy efficient lights only need to be burned a few hours, he says, to make up the difference between the length of summer and winter days. A timing device can easily be rigged to turn the fluorescent lights on for a few minutes before sunrise and again for a brief period following the natural sunset.

The greenhouse owner trying such a scheme, however, should be aware that some plants — such as soybeans and poinsettias — actually need short days to flower, and that beans, tomatoes and other "day neutral" plants — with little regard for how long they receive light each day — bloom whenever the other environmental factors (temperature, carbon dioxide, water and minerals) are to their liking.

The practice of extending the day's photoperiod may be necessary only for the serious grower located in extreme northern or southern areas of the globe, or for the greenhouse manager raising certain commercially valuable crops.

CONTROLLING INSECTS AND DISEASES

SANITATION AND PLANT MANAGEMENT³

No greenhouse is trouble-free, but if you want to grow crops the easiest way possible, without constantly fighting diseases and insects, remember one word — sanitation. The inside of a greenhouse is actually a "hothouse" in which disease organisms and insects can find the right temperature and humidity for rapid multiplication. The best way to control insects, bacteria, fungi and viruses is to keep them out in the first place. Once they've gotten to a plant, control is difficult.

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