Читать книгу Manual of American Grape-Growing - U. P. Hedrick - Страница 28

The average date at which the last killing frost occurs in the spring often determines the limit in latitude at which the grape can be grown. Even in the most favored grape region of the continent, killing frosts occasionally destroy the grape crop, and there are few seasons in which frost does not take some toll. Thus on May 7, 1916, frost all but ruined the crop of wine- and table-grapes in the great grape region of northern California where frosts are seldom expected in May. Little or nothing can be done to protect grapes from frost. Windbreaks as often favor the frost as the vine, and smudging or heating the vineyards is too expensive to be practical. In growing grapes, therefore, the commonly recognized precaution of selecting a site near water, on slopes or in a warm thermal belt must be exercised.

The limits of grape culture are also determined by early autumn frosts. The grape stands two or three degrees of frost, but anything lower usually destroys the crop. Here, again, the only precaution is to take pains in selecting the site.