How Do Grapevines Bloom?

Grape Types

• Species of Euvitis, including Vitis vinefera and Vitis labrusca, are true grapes that hang in bunches. Vitisus vinefera, used to make wine, includes such species as pinot noir, merlot and zinfandel. Concord is a type of Vitis labrusca, the species native to North America that is used for juice and to make jams and jellies. Muscadine grapes (Muscadinia rotundifolia), a small juice-grape native to the southeastern United States, produces a different kind of flower.

Flower Description

• Grape flowers grow each spring on branching clusters opposite the base of new leaves. Each 1/8-inch-wide flower has five sepals, petals and stamen. Sepals are green leaf-like structures that form the protective calyx at the base of a flower. The stamen is the male part of the flower that bears the anther, a sac of pollen. Some Euvitis species have more than 100 flowers on each cluster. Muscadine grapes have from 10 to 30 flowers.

Pollen Requirements

• Euvitis species are flower perfect or self-fruitful, meaning they do not need pollen from other flowers. Self-fruitful flowers have both female ovaries and male stamens. Some cultivars of muscadine grapes have flowers that are pistillate, meaning they have female pistils but no male stamen and so need pollen from other flowers in order to produce grapes.

Flower Growth

• When your grapes flower depends on the weather and the variety of grape. The button-like tips of new shoots will develop into clusters of flowers about 10 weeks after the buds break. Flowers will usually appear when the temperature is from 59 to 68 degrees F. At first, you'll only see the nubs of protective calyx. These will eventually fall off, freeing the pollen from the anthers. Heavy rain, very hot or cold weather, or hard wind might cause your yield to drop or result in bunches of grapes that are too compact.