Читать книгу Manual of American Grape-Growing - U. P. Hedrick - Страница 26
The seasonal sum of heat.
ОглавлениеSuccessful cultivation of the grape depends on a sufficient amount of heat during the summer season. The theory is that buds of the grape commence to start when the mean daily temperature reaches a certain height, and that the sum of the mean daily temperature must reach a certain amount before grapes ripen. Manifestly, this sum must vary much with different varieties, low for the earliest sorts, high for the latest. There have been many observations as to the temperatures at which buds of the grape start growth, so that it is now known that the temperature varies in accordance with locality and degree of maturity. Roughly speaking, grape buds start at temperatures from 50° to 60° F. The seasonal sum of heat for ripening is probably 1600 to 2400 units. A variety ought not to be planted, therefore, in a region in which the average seasonal sum of heat is not sufficiently high. The seasonal sum of heat can be determined for a locality from data published by the United States Weather Bureau; and by comparing with the sum of heat units in localities where a variety is known to thrive, the grape-grower can determine whether there is sufficient heat for any particular variety.
The grape seldom suffers from hot weather in a grape region. The fruit is sometimes scalded in the full blaze of a hot sun, but the ample foliage of the vine usually furnishes protection against a burning sun. At maturing time, the heat of an unclouded sun, if the air circulates freely, insures a finely finished product. Deep planting helps to offset the harmful influences of warm climates.