OUR SUN-HEATED GREENHOUSE

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A SECOND HAZARD

The second hazard is snow and ice. Snowfall may be a problem in its own right; it is certainly an effective check on gardening. Its aftereffects may be even more serious. A New England snowstorm, driving in from the northeast, may include rain which melts part of the snow. If the storm ends by a wind shift into the north, the resulting drop in temperature turns slush and snow into a treacherous ice sheet that covers trees, highways, gardens, and footpaths. Work in the open is brought to a halt, with foot passengers and drivers alike picking their way with care, or calling it a time to hibernate.

Equipped with a glass roof, a greenhouse is especially hampered by snow and ice. A snowstorm cuts off light; it also adds to the roof load. If the snow is freezing as it falls, it hardens onto the greenhouse roof and stays there until it is softened up eventually by higher temperatures. We aim to keep the greenhouse roof clear of snow. We have a wooden snow-pusher with a long, light handle. As soon as snow has had a chance to soften up on the roof we push it off and let in the light.

FROZEN GROUND

A third winter hazard is ground frozen so hard that it cannot be worked in the unheated greenhouse. This situation is avoided or postponed by sprinkling, before the ground hardens, a moderate layer of dry autumn leaves over any greenhouse earth that is not covered by foliage. A little experience will show how thick the layer of dry leaves should be. We know that if lettuce and other such plants have a light mulch of dry autumn leaves thrown on them it helps them to survive. Even on a sub-zero night the ground covered by such a mulch may be unfrozen.

We have checked this point on a bit of land covered by a thick growth of soft maple, white birch, and pin cherry. If the normal leaf cover on such a piece of woodland is undisturbed there will be two or three inches of dry leaves that can be kicked aside, revealing an unfrozen forest floor. Unless the ground is water-soaked, the leaves have curled up and are able to keep large air spaces between leaves . . . which prevent the ground from freezing.

If any of the soil in the cultivated area of the greenhouse is exposed, keep it stirred up with a light stick or a small tool, even when it looks as dry as dust. Really dry ground cannot freeze; it is the water in the ground that freezes.

Another hazard is the succession of freezings and thawings that the plants may have to undergo in an unheated greenhouse. One or two such experiences may not prove fatal, but too many might finish off delicate plants. The foliage of most hardy or semi-hardy plants will survive a great deal of freezing and thawing unless there are juicy stems or other exposed parts that get iced up. Deal with this difficulty by not touching frozen, brittle plants that may break off before they thaw.

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