Manual of American grape-growing

by U. P. Hedrick

Spring and autumn frosts.

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.

The use of weather data and dates of life events of the grape.

These considerations of length of season, humidity and spring and fall frosts make it plain that the grape-grower must synchronize these phases of climate with the life events of the grape. In particular, he must study weather data in relation to the blooming and ripening of grapes. Usually, the necessary weather data may be secured from the nearest local weather bureau, while the date of blooming and ripening may be obtained from the state experiment stations in the states where the grape is an important crop.

Winter temperature.

Varieties of native grapes are seldom injured in America by winter-killing, since they are usually planted in climates in which wild grapes withstand winter conditions. Native varieties follow the rule that plant and climate are truly congenial in regions in which the plant thrives without the aid of man. A few varieties of native grapes fare badly in the winter's cold of northern grape regions, and the tender Vinifera vine is at the mercy of the winter wherever the mercury goes below zero. In cold climates, therefore, care must be exercised in selecting hardy varieties and in following careful cultural methods with the tender sorts. If other climatic conditions are favorable, however, winter-killing is not an unsurmountable difficulty, since the grape is easily protected from cold, so easily that the tender Viniferas may be grown in the cold North with winter protection.

Air currents.

Currents of air are of but local importance in growing tree-fruits, but are of general and vital importance in growing the grape. The direction, force and frequency of prevailing winds are often controlling factors in the suppression of fungous diseases of the grape, and the presence of fungi often means success or failure in regions in which the grape is planted. Winds are beneficial, too, when they bring warm air or dry air, and when they keep frosty air in motion. The air must move in all grape regions, whether from cañon, mountain, lake or sea. Sunlight, warmth, and air in motion are life to the grape. Sometimes winds may be detrimental; as when too cold, too blustering, or when they bring hail, the latter being about the most disastrous of all natural calamities. Windbreaks are of small value and are often worse than useless. Having planted his vineyard, the grape-grower must take the winds as they blow.