Rosie Lerner, Purdue Consumer Horticulture Specialist
One of the toughest things about growing your own grapes is beating the birds to the harvest! Could it be that the birds know something we don't? Netting can be placed over a grape arbor to keep the birds away from the fruits. But don't be too hasty in cutting the fruits to one-up the birds. Make sure your grapes are ripe before you harvest.
Although color change is important in determining when to harvest grapes, it should not be the only consideration. Most berries change from green to blue, red or white (depending on the cultivar) as they approach maturity. But most grape cultivars color up long before they flavor up. When fully ripe, the natural bloom or whitish coating on the berries should become more noticeable. The color of the seeds changes from green to brown.
One of the other factors to consider in determining harvest time is the size and firmness of the berry. It's helpful to be familiar with your cultivar's individual characteristics, but most grapes should become slightly less firm to the touch.
The best telltale sign of ripeness is the grape's sweetness, and, of course, the most reliable method for homeowners to test this is to taste them! Unlike some other fruits, once the grapes are cut from the vine, they will not ripen any further. So, be sure the grapes are ready before you harvest.
Grapes don't require direct sunlight on the fruits to ripen and develop good color. Rather, it is the amount of light that reaches the plant's leaves that governs the quality of the fruit. The leaves manufacture the sugars that are then translocated to the fruit. To protect your ripening crop from hungry birds, you can place bags over individual fruit clusters beginning when the grapes are about half grown. Use a sturdy brown paper-type bag that will allow enough room for the bunch to develop, and tie securely to the grape cane. Bagging also might help protect the fruits from inclement weather, as excessive rains close to harvest time can cause the grape's skins to split. Of course, bagging is not very practical for larger plantings, in which case netting is the best alternative.
Some grape-growers have experienced uneven ripening this year, particularly with their concord grapes. According to Purdue University Small Fruit Specialist Bruce Bordelon, this condition is known to only on the Concord variety and occurs occasionally, especially in warm years. Uneven ripening is when some of the berries in the cluster remain sour, hard and green while others develop the purple color and soften during the ripening process. The green berries will be full-sized, but will not be sweet. For some reason, those berries never go through the increase in sugar and decrease in acids that commonly occurs during fruit ripening. It is not clearly understood why this phenomenon occurs, but hot weather is partly responsible.
Once you've made the decision to harvest, you can store the grapes, possibly up to eight weeks, depending on the cultivar and storage conditions. Ideally, grapes should be stored at 32F with 85 percent relative humidity. If you have an abundance of grapes, there are some good alternatives to eating them fresh. Grapes are excellent for making jellies, jams, juice and wine.
Last updated: 10 April 2006
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