When Do Grapes Ripen on the Vine?

The Plant

• The plant is a sprawling vine and must be supported and trained if being grown for an intended harvest. Many wild grapes are unreachable due to the heights to which they climb. Training a grapevine to cling to a man-made structure, whether an arbor or a high tensile wire "fence," requires that during the second year, the two strongest canes be selected and any other shoots be cut away. Allow a few shoots to grow about 4 feet off the ground, and attach these shoots to the support by constantly checking on them and guiding them to grab onto it as they grow. During this time, cut off any blooms to prevent the vine from bearing fruit. The third year should see a well-trained grapevine that is permitted to bear fruit.

Determining Ripeness

• Telling whether or not grapes are ripe for the taking can be somewhat tricky. They change color from green to their ripened color before the fruit actually is ripe for eating. Therefore, unlike most berries, color is no indication of readiness. Large vineyards use a refractometer to measure the sucrose level of the berries, taking the guesswork out of grape harvest. The backyard grower with a vine or two can use touch and taste to determine ripeness. A ripened grape loses some of its firmness, and tastes sweet. When you cut into a fully ripe grape, the seeds inside will be brown instead of green.

Harvesting Time

• Due to the wide variety of grapes and their different growing requirements, grapes can ripen before Labor Day until the first killing frost. Be sure not to pick grapes prematurely; unlike many other fruits they will not ripen once plucked, and when the leaves die on the plant, no further ripening takes place.

Sharing

• While grapes do not suffer from many insect pests, they are favored by many wild animals, especially birds. Raccoons, opossums and skunks also are fond of the heavy clusters of fruit. The only deterrent for birds is netting, or in the case of single vines, a paper sack placed over ripening clusters and tied loosely to the stem does the trick. Since grapes do not absorb sunlight directly but through the plant's leaves, being enclosed neither hastens nor stalls ripening, and may protect them from bad weather by keeping the skins from splitting open. A single strand of electric fence wire placed 6 inches off the ground may help keep wandering animals at bay.