Deciduous, Edible fruit, Vines
Most grapes are grown for fresh fruit, wine, shade, and fall color, but there are also common ornamental grapes: see Vitis coignettiae. A single grapevine can produce enough new growth every year to arch over a walk, roof an arbor, form a leafy wall, or provide an umbrella of shade over a deck or terrace. Grape is one of the few fruiting vines that offer bold textured foliage, colorful edible fruit, and a dominant trunk and branch pattern for winter interest. To produce good-quality fruit, you must choose a variety that suits your climate well, train it carefully, and prune it regularly.
There are several basic grape types: European, American, and American hybrids.
Almost all grapes are self-fruitful and do not require pollination from another variety to bear fruit—but since they differ greatly in hardiness and heat requirements, choosing the right type and variety is important.
Support. Once they are established, grapevines are rampant. Provide a sturdy trellis, arbor, chain-link or rail fence, or a wall strung with wire to support these big vines and their heavy bunches of fruit. To build a custom wire trellis large enough to accommodate two grapevines, set stout posts in the ground 15–20 ft. apart; posts should rise 5 ft. above the soil. Set two smaller posts (support stakes for the vines) 4–5 ft. from the end posts. String sturdy galvanized wire (10- or 11-gauge) across the four post tops. For a double-wire trellis, string a lower wire at the 2 1/2-ft. level. Space multiple trellises 10–12 ft. apart.
Planting and care. Purchase year-old bare-root vines, and plant during the dormant season (winter in mild-winter regions, about 3 weeks before the last expected frost date in cold-winter areas). Trim roots to 6 in. just before planting in holes spaced 8–10 ft. apart. If planting at an arbor or fence, position each hole about 1 1/2 ft. away from the structure, and set the plant at a 45° angle so it leans toward the support. Cut back top growth to two or three buds. Place vines as deep in the soil as they grew in the nursery, spreading roots in all directions. In some areas, planting deeper, with all but the top bud buried, is recommended; check with a local nursery or Cooperative Extension Office.
Water and weed regularly. Grapes are prone to fungal diseases, so avoid splashing water on leaves; drip irrigation is ideal. Fertilize each spring with a balanced fertilizer; for newly planted vines apply one-fourth the amount recommended on the bag, then gradually increase the amount each year until the fourth year, when you can start applying the full recommended dose each spring.
Initial training. If all you want is a leafy cover for an arbor or patio, you need only train a strong vine up and over its support and thin out entangling growth each year.
But most people plant grapes for the delicious fruit. To prepare grapevines for good production, train them into a basic framework on an arbor or wire trellis.
The first summer after planting, let each vine grow unchecked from the base of its support structure.
During the first winter, select the sturdiest shoot for the trunk and tie it to the support; shorten it to the three or four lowest buds and remove all other shoots at their base.
In the second spring, once the buds have grown out to 6–8-in.-long shoots, choose the strongest upright shoot for the continuation of the trunk and tie it to the post. (If you’re training plants on a two-wire trellis or against a fence, also select two strong lower shoots for “arms” and tie them to the lower horizontal support.) Cut off all other shoots.
If you’re growing your grapevine on a wire trellis, the second summer is the time to stop its vertical ascent. When the trunk reaches the top wire of the trellis, pinch it back to force branching. Train the two strongest resulting shoots along the top wire and remove any others. (For a two-wire trellis, also tie the lower arms’ new growth along the lower wire; pinch back any lateral shoots developing from those arms to about 10 in. long.)
In the second winter, cut back all growth on the trunk and arms and make sure that both sets of arms are loosely tied to the wire.
During the third summer, allow the vine to grow but remove any shoots sprouting on the trunk. At this point, you’ve established a permanent framework for your trellis-grown vine, and you can choose between cane pruning and spur pruning from the third winter on (see “Yearly pruning,” below).
If you’re training your vine onto an arbor, the second summer is the time to direct its growth onto the roof of the structure. When the vine has grown just beyond the top of the vertical support, gently bend it over and secure it to the roof as it grows. Remove side shoots to encourage the tip to grow.
During the second winter, cut back the main stem to a point just beyond where you want the last set of branches. Cut off all the side shoots.
During the third spring, thin new shoots to 1 ft. apart.
In the third winter, you’re ready to create the final framework; its form depends on how you plan to prune your vines in subsequent years. If you’re planning to do spur pruning, cut back each of the shoots you selected in the spring to two buds. If you will be cane pruning your vines, cut branches alternately to long canes (12 buds) and spurs (two buds).
Yearly pruning. Grapes are produced on stems that develop from year-old wood stems that formed in the previous season. These year-old stems have smooth bark, whereas older stems have rough, shaggy bark. The purpose of yearly pruning is to limit the amount of potential fruiting wood to ensure that the plant doesn’t produce too much fruit and that the fruit it does bear is of good quality. Pruning should be done in the dormant season—that is, in winter or earliest spring before the buds swell.
The two most widely used methods for pruning grapevines are spur pruning and cane pruning. Begin using either method in the third winter, and repeat yearly thereafter.
Spur pruning. Start by removing weak side shoots from the arms. Leave the strongest shoots (spurs) spaced 6–10 in. apart; cut each to two buds. Each spur will produce two fruit-bearing shoots during the next growing season. The next winter and every winter thereafter, remove the lower shoot on each spur and cut the upper stem to two buds. Those buds will develop into stems that bear fruit the following summer.
Cane pruning. Select one strong lateral shoot near the trunk on each arm, cut it back to 12 buds, and tie it to the support; these will produce fruiting shoots in the coming summer. Select another strong lateral shoot near the trunk on each arm, and cut it back to two buds; these will be the renewal spurs. Remove all other shoots. Each winter, remove the arms that have fruited, and choose as their replacements the two longest and strongest shoots that grew from the renewal spurs. Cut each to 12 buds and tie the two shoots to the support; select the two next-best shoots as renewal spurs, and cut each to two buds. Remove all other shoots.
Pests and diseases. Pierce’s disease, caused by a bacterium spread by the sharpshooter insect, is a serious threat to grapes in California. It causes afflicted vines to lose productivity, wilt, and die in a matter of only a season or two. For more information, contact your Cooperative Extension Office.
The grape leafhopper may cause leaf drop on grapevines in California. Get rid of nearby weeds, which may harbor the pest. Spraying with insecticidal soap is somewhat effective; grape leafhopper infestations are rarely serious enough to warrant a stronger pesticide. Grape mealybug may infest vines in the Northwest and parts of California; control with horticultural oil spray in late winter.
Powdery mildew is a serious disease of European grapes (most American varieties are immune). To control, dust vines with sulfur when shoots are 6 in. long, again at 12–15 in. long, then every 2 weeks until harvest.
From Europe. These have a tight skin, a generally high heat requirement, and cold-tolerance to around 5°F/–15°C. These are the table grapes of the market, including ‘Thompson Seedless’. The classic wine grapes, such as ‘Cabernet’, ‘Chardonnay’, and ‘Pinot Noir’, are also European in origin. Leaves are 2–6 in. wide and rounded, with three to seven lobes. Fruit matures in autumn.
The popularity of European grapes, especially wine varieties, has led to their being tried beyond their normal range. In cold-winter climates, the crop may be ruined by spring frosts and summer rains in some years, but vines that are protected or planted in warm microclimates can produce harvestable fruit in other years. Even in Hawaii, European wine grapes are being successfully grown in some high-elevation areas. At lower elevations, where grapes are ravaged by the hard-to-control Chinese rose beetle, crops are rarely successful.
This seedless red grape is excellent for fresh eating and for raisins. Very vigorous. Keep it on the dry side to reduce vigor and encourage ripening. Fruit matures at early midseason.‘Thompson Seedless’
Produces big clusters of small, sweet, seedless, greenish-amber fruit at midseason. For fresh eating and for raisins. It’s widely planted but it does best in hot, dry areas.
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