Growing Grapes in Your Backyard
Irrigation is essential for good vine growth and production. Grapes will adapt to low water conditions, but fruit production will be reduced. Applying water deeply and thoroughly filling the root zone with water is an ideal way to irrigate. Irrigation frequency will depend on the soil type and depth, the rooting depth of the vines, and the weather. Furrow irrigating every 2 weeks in the summer is usually adequate under good soil conditions and a moderate climate. Grapes may require more frequent irrigation in hot climates, as in the inland valleys. Drip irrigation is also an excellent method, although the frequency of irrigation should be increased to once a week or more often.
Generally, a fully trellised mature vine on a hot day in the Central Valley requires about 8 to 10 gallons (30.3 to 37.9 l) of water per day. Vines that are less vigorous or untrel¬lised require 6 to 8 gallons (22.7 to 30.3 l) of water per vine per day. Table 15.4 is a drip irrigation schedule for an average trellised vine. These figures are for the Central Valley and should be used only as a guide. In areas along the coast and in northern parts of the state, the rates will be lower. Requirements in the southern part of the state should be similar to the Central Valley irrigation schedule. Check the soil profile to be sure that the plants are getting adequate water but not too much. For the best quality, wine grapes should be irrigated somewhat less through the season than table grapes.
Timing of irrigations is a critical factor for producing the best quality grapes. Avoid water stress from the bloom period to berry softening, which occurs when berries give in to finger pressure. Usually, color begins to appear on colored varieties at the same time. Fruit on the vines may succumb to cracking if the vines are allowed to dry and then wetted again. Maintain an even level of soil moisture to avoid cracking. Also avoid excessive irrigation to prevent having more vine than fruit.
Drip Irrigation Schedule for Grapes in the Central Valley, Table 15.4 (pdf). UC. Buy Publication