Features
What Do Organic Growers Do About Growing in Greenhouses?
The organic greenhouse is similar to the organic garden. A diversity of plants maintained with natural fertility and without the use of potentially dangerous chemicals. While the extra warmth results in plants growing better indoors, it's the protection from the wind and rain that is of greatest benefit to plants. Cold winds and heavy rainfall can seriously affect the health of even the strongest plants.
Border soil
Planting into border soil is the favoured method of organic gardeners. While using only border soil will mean less total space for plants, the health, yield, and taste of plants grown in natural soil will justify this traditional method of greenhouse growing. And provided you maintain a high level of fertility, plants can generally be grown closer together than most text books recommend. Maintaining fertility in the smaller glasshouse area is much easier than in the garden.
Sterilising
Many greenhouse owners sterilise their soil once a year. Most of the chemicals used in this process would be unacceptable to the organic gardener. Anyway, few organic gardeners believe in sterilising their soil. Sterilisation destroys diseases and pests but it also destroys many beneficial microorganisms as well. To the organic gardener a sterile soil is not a living soil.
Fertility
Fertility is maintained in the greenhouse as in the organic garden by digging in copious amounts of garden compost or dung every year. You need to be doubly sure that the organic material used is well composted as diseases and pests can spread rapidly in the extra warmth. Calcified seaweed, bonemeal, or wood ash can also be added, depending on your soil and the specific needs of your plants. During the growing season fertility can be topped up with a foliar feed of comfrey, nettle tea, or liquid seaweed.
Ventilation
Perhaps the biggest problems in the greenhouse are the diseases caused by inadequate ventilation. Striking the right balance between sufficient heat and sufficient air can be a problem, but it is generally better to err on the side of air! Especially in the misty autumn when fungal diseases are rife.
Pests
With a suitable diversity of healthy plants pests should not be a major problem. However white fly can be a scourge of the greenhouse so plant a few marigolds to repel them. Marigolds grow very well beside tomato plants. If your greenhouse does become infested, soft soap and water will eliminate the problem.
Winter
As in your garden, it's better to keep the soil life working during the winter rather than leave it bare. So if you are not planting any winter crops, sow a green manure when you have the house clear after the summer. Rye or mustard are two suitable varieties. But it's a pity not to use at least some of the greenhouse area to give you a supply of greens over the winter. You are probably fed up with greens by now but by Christmas you will be glad of some fresh lettuce, chicory or endive to refresh your palate after devouring the annual big bird.
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