When Do People Harvest Grapes?

Training Years

• When starting grapevines, you must allow two to three years before the vines can support grape clusters. Cut a first-year planting back to two or three buds, and let the shoots grow and produce many leaves to encourage the root system to grow strong and healthy. The second year, cut out all but two sturdy canes and allow three or four shoots to grow on the trellis. Prune any flower clusters that form. By the third year, regular pruning should begin, and you can expect your first grape harvest in late summer or early fall depending on the cultivar you're growing.

Color

• When grapes begin to change color, the ripening and flavoring process begins -- this is the first sign of grapes approaching maturity. Young grapes are generally green, and some cultivars turn black, blue, purple, red, pink, bronze or white as they approach harvest time. When the grapes are ready to harvest, a whitish coat becomes visible on the skin and the seed color turns brown.

Firmness

• Each cultivar has its own preferred characteristics. Therefore, reading up on the optimal size and firmness for your cultivar will help you better gauge when your grapes are ready to harvest. According to Purdue University Consumer Horticulture, "Most grapes should become slightly less firm to the touch."

Sweetness

• The most reliable sign that it's time to harvest your grapes is the amount of sweetness. For home gardeners, tasting several grapes from different areas of the vine and field can tell you all you need to know. As the grape color deepens, sugar levels rise as acid decreases. If you plan to sell your grapes at market or create your own wines, you may want a more scientific reading of the sugar levels from a refractometer. Depending on your cultivar, the acceptable sugar content reading ranges from minus 14 to 24 degrees Brix. The preferred acidity of table grapes is .6 to 1.0 grams per liter, with a pH between 3.0 and 3.5.

Time of Day

• Picking wet grapes increases the risk of severe post-harvest diseases. Therefore, wait until the morning sun dries out all the dew to pick the grapes. Good weed control and regular mowing between the rows can also help keep the fruit dry to prevent quality damage caused by excess moisture. Delay in harvesting the grapes once they are mature can result in fruit drop, decay, cracking and crop loss to wasps, yellow jackets and birds.