Structures

Structures on which the vines may be trained range from two or more posts set in the ground and strung with two or three horizontal wires (a trellis) to decorative arbors. Bracing should be sufficient to carry the weight of vines and crop under the sort of wind conditions experienced in the area. Trellis posts should not be more than 20 feet apart and arbor posts not more than 10 feet apart.

Wires (11- or 12-gauge smooth galvanized) should be spaced about 2 feet apart up the posts or along the top of an arbor. Closer spacing causes excessive shading. To permit weed control under the vine and to keep the fruit up, the lowest wire should be 30 to 36 inches above the ground.

Train a permanent trunk to the top wire of a trellis or to the top edge of an arbor.

During the dormant season when vines are pruned, fruiting canes (see below) should be trained outward along each wire on the trellis or along an arbor's top edges.

Each bud on the fruiting canes grows into a shoot from 4 to 20 feet long. These are tied along trellis wires as they grow, or on an arbor are spaced out across the top wires to give even exposure to sunlight.

Fruiting canes can be readily identified if we look at a vine in the spring before growth begins. They are the one-year-old shoots (wood of the previous season), with bark that is smooth and brown. At each place where a leaf grew the previous season, there is a conical swelling, or bud.

During the growing season, each bud grows into a shoot which bears leaves and generally three clusters of grapes. The more buds that are left after pruning, the more clusters will appear on the vine.

An unpruned grape vine will set far more fruit than it can ripen successfully. Fruit from overcropped vines is low in sugar, sour, and has poor color. Excessive over-cropping can severely damage the vine.

Obviously the cluster size must be considered in calculating size of a crop. With very large clustered varieties, such as Thompson Seedless, as few as 10 clusters per vine (8-foot spacing) should be left. Perhaps 50 clusters of Concord can ripen and as many as 100 of small clustered varieties such as Beta or Foch.

The commercial grower controls crop size by leaving exactly the right number of buds. The home gardener can achieve a far more accurate control of crop size, and do it despite variations in weather or fruitset, by leaving an excess number of buds two or three times as many as needed, and removing clusters until the right number remain. Removal of excess clusters can be done any time from before bloom until mid-season.

Black rot fungus on an American bunch grope leaf.

Pest Control

Most county Extension offices have spray schedules for the home gardener and in those areas where grapes are grown, appropriate sprays for diseases and insects of grapes are included. You may be able to get an occasional crop without spraying, but both diseases and insects tend to become progressively more severe from year to year.

Control of weeds for a foot or two around young vines is worth the effort in the improvement of growth You can expect. Once established, the vine will shade out some weed growth.

Some types of weedkiller should not be used near grapes as they are extremely sensitive. Do not use the combination of fertilizer plus weedkiller on lawn areas within 15 feet of a grape vine. The weedkiller may be picked up by the grape roots that extend out this far and the vine can be damaged.

In many areas birds can be a major problem. Netting, which can be used earlier in the season for strawberries and blueberries, is available and if placed carefully over the vines will protect the fruit.

Hornets and wasps on ripe fruit are a common complaint. They are able to attack, the fruit only if it has been damaged by insects, diseases or birds, or if it is overripe.

An acceptable taste is the main criterion for table use. On a vine that is not overcropped, the berries of blue varieties will lose their red color and white varieties will change from green to golden yellow. Ripe berries will soften and seeds become brown.

As the berries ripen, sugar content rises while the acid level decreases. Both these changes are reflected in improved taste.

Determining the harvest of wine grapes requires either experience or a means of measuring both sugar and acid levels.

The yields of a grapevine greatly affect fruit quality. If you permit vines spaced at 8 feet to produce over 30 pounds of fruit each, the quality will almost surely be low. Only under ideal circumstances and climates can this size crop be ripened successfully.

It is better, especially on young vines, to leave a smaller crop than optimum, say 5 to 10 pounds of fruit, until you find out how much fruit can be ripened successfully in your particular situation.

There are several sources of information at all levels of complexity for the home grape-grower.

The U.S. Department of Agriculture and State Agricultural Experiment Station bulletins and leaflets cover general grape growing, variety recommendations, descriptions of diseases and insects, pests, and recommended spray programs. States which have an established grape industry tend to have more complete and extensive publications.