Grapes (Vitis spp.) have an undeserved reputation for being difficult to grow. When Lief Eriksson arrived in North America, he dubbed this continent "Vineland" because so many grapes grew wild. Grapes thrive in U.S. Department of Agriculture plant hardiness zones 2 through 10, making them a suitable crop for almost every part of the country. If your grapes aren't producing fruit, the problem is probably related to growing conditions or care. If the vines show other symptoms, such as leaf curling or leaf spots, consider the possibility of disease.
Incorrect growing conditions can delay or prevent fruiting. Grapevines grow best in light, well-draining soil. Heavy clay soils impede growth and fruiting. In rich soils, the vines produce lots of extravagant foliage, but few grapes. In the spring, spread 10 ounces of 10-10-10 fertilizer around the base of each vine. Grapes need at least six to eight hours of sunlight daily to produce fruit. Plant grapevines in a sunny, sheltered area, protected from winter winds and frosts. Water grapevines weekly, or as needed, to keep the soil slightly moist, but not overly wet.
Your grapevines might not be producing fruit because they are too young. Grapevines often won't produce fruit for at least the first two or three years. In some cases, they might take five or six years to produce a satisfactory crop. Prune any developing fruit out during the first two years so the vines can focus on developing strong roots.
Perhaps the reason your grapevines aren't producing fruit is because you've selected a variety that isn't adapted to your region. American hybrids, such as "Concord" (Vitis labrusca "Concord") and "Niagara" (Vitis labrusca "Niagara") thrive in the cool climates found in USDA zones 2 through 6. European hybrids (Vitis vinifera) and muscadines, including "Scuppernong" (V. rotundifolia "Scuppernong") grow best in USDA zones 7 through 9. Many muscadine grapes need another plant to pollinate them. Without a pollinator, these grapes won't produce fruit.
Grapevines can live for 100 years or more, but they won't remain productive without annual pruning. Left untended, the vines produce long, rambling growth, which slowly reduces fruit production. If your vines have been neglected, cut back all the old canes that have previously borne fruit to the arms, which are the main stems from which all the canes grow. Leave up to 10 healthy nodes on the arms. These nodes, or buds, will produce new canes in the spring. You should have two or three sets of arms, each stretching out in opposite directions along the trellis. Remove any other stems that form from the main stem. Trellis the vine to a strong support or arbor if you haven't already. Prune grapevines in late winter, before new growth emerges.
Disease and Pests
Occasionally, grapevines might not produce fruit because of an insect or disease problem. In these cases, you'll almost always notice other symptoms. American grape varieties are immune to phylloxera, but this insect pest can wreak havoc among European grape varieties. This insect pest feeds on the roots of grapevines, eventually causing the plant to wither and die. Plant resistant varieties if you suspect phylloxera in your area. Bunch rot is a common disease that causes rotting fruit and withered leaves. Powdery mildew causes a white growth to form on leaves and fruit. In severe cases, it can reduce fruit growth. In both cases, growing grapes in full sun and spacing them so air circulates freely can reduce disease problems. Annual pruning opens the vines up to more light, which also helps cut back on disease issues.
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