Even if the stand of the fall
crop is satisfactory, there is always the danger of winter-killing
to be reckoned with. The real cause of winter-killing is not yet
clearly understood, though it seems that repeated thawing and
freezing, drying winter winds, accompanied by dry cold or protracted
periods of intense cold, destroy the vitality of the seed and young
root system. Continuous but moderate cold is not ordinarily very
injurious. The liability to winter-killing is, therefore, very much
greater wherever the winters are open than in places where the snow
covers the ground the larger part of the winter. It is also to be
kept in mind that some varieties are very resistant to
winter-killing, while others require well-covered winters. Fall
sowing is preferable wherever the bulk of the precipitation comes in
winter and spring and where the winters are covered for some time
with snow and the summers are dry. Under such conditions it is very
important that the crop make use of the moisture stored in the soil
in the early spring. Wherever the precipitation comes largely in
late spring and summer, the arguments in favor of fall sowing are
not so strong, and in such localities spring sowing is often more
desirable than fall sowing.
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