Grape vines need well-drained soil and should have at least 20 in. of topsoil. They don't need very fertile soil because of vigorous, extensive roots; vines that grow more slowly also develop more "character." Plant vines at the same depth as grown in the nursery. Mound soil over the crown to prevent wind damage, except in the West because of possible crown rot. Cut out all but 1 or 2 stems (with 2-3 buds each) for the central trunk. Grape roots prefer warm soil, so mulch with stones or black plastic to raise soil temperature. If vines overbear, thin flowers before berries form.
Cut bunches when fruits are fully colored, sweet, and slide off easily, and the stems and seeds are brown. Grapes don't ripen further once picked. For raisins, use a hydrometer and harvest when the grapes reach 20% soluble solids. A lower percentage significantly decreases raisin weight and quality.
Cool to 50°F as soon as possible after picking and spread out fruit bunches in single layers. Dry in the sun under clear polyethylene; this shortens drying time and yields better raisins with higher levels of sugar and vitamin C than raisins dried in an oven. Dry until stems shrivel slightly, then store in trays no more than 4 in. deep. Fresh grapes can be stored at 40° for 2-3 months.
Height - Pruned: 12-20 ft. Unpruned: 50-100 ft.
Spacing - 8 ft. is best; 7 ft. in shallow soil, and 10 ft. in deep soil.
Root Depth - In deep soil they can easily extend 12-40 ft.
pH - 6.5-7.0
Bearing Age - 3-4 years
Pollination - All are self-fertile with the exception of a few muscadine vines.
Chilling Requirements - None
Site - Best on a 15° south-facing (SE or SW slope)
Water - Low to dry. To harden the vines for winter, don't water much after August.
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Fertilizer - Apply compost only at the beginning of the grwoing season or during blooming. When applied late in the season, nitrogen delays ripening, inhibits coloring, and subjects vines to winter injury if they keep growing too long into the fall. American grapes and hybrids are especially sensitive to N-deficiency in the early spring and during blooming.
Training - For vigorous vines, the Geneva double curtain method provides the best aeration, most sun, and highest yields. Plant vines down the center, prune each to 2 trunks, and grow trunks to long, 6-8 ft. cordons on upper wire. Train the first vine to the front wire, the second to the back wire, and so on. The more common 4-arm Kniffen method provides an attractive privacy screen but shades the lower vine parts. For both methods, bury 9 ft. end posts 3 ft. in the ground. Use heavy galvanized #11 wire.
Pruning - For each selected fruiting cane, choose a cane nearby as a renewal spur for next year's fruit; cut back to 2 buds. Each year replace the fruiting arm with a cane from a renewal spur, and select new renewal spur for the following year.
Grape Pests & Diseases
Leafhopper, grape berry both, Japanese beetle, phylloxera beetle, root aphid, plum curculio, mealybug, mite, rose chafer.
Anthracnose, black rot, botrytis, fruit rot, crown gall, downy mildew, leaf spot, powdery mildew, Pierce's disease (spread by leafhoppers).