Understanding the cycles of growth, harvest and leaf decomposition can help you become successful in growing grapes. Many factors go into growing healthy vines: climate, soil conditions and the characteristics of the grape variety. They do best in temperate climates. They are well adapted to home gardens but need wire or trellis supports. A basic understanding of the stages of growth will help you get started.
In the spring buds begin to break through on the grapevines, which have been dormant all winter. The pruned branches begin to show moisture and the green buds become visible. Each bud contains three primordial shoots that become the new vines and grape clusters. Within four weeks the bud growth is rapidly accelerating. Young buds are susceptible to frost; they need a warm climate above 50 degrees F
Flowers develop on the vines in 40 to 80 days after the buds set. They look like small buttons. Variations in weather can slow the flowering process. Pollination and fertilization take place during this stage. Most grapevine varieties are self-pollinating. Pollination produces the seeds as the flowers develop into grape berries.
Grapevines begin to set fruit almost immediately after flowering. The grape berry forms to protect the new seed. Flowers that have not been pollinated eventually fall off. Between 30 and 60 percent of flowers fertilize and become grapes. Low humidity is important to set fruit. High temperatures and water stress are negative influences on the amount of fruit set.
The ripening stage begins about 40 to 50 days after the fruit has set. The grapes have grown to about half their final size, hard to the touch and either green or red/brown, depending on the variety. Now they begin to rapidly increase their fructose and glucose levels, and their acid content begins to fall. The vines also begin to put some of their energy into next year’s growth.
In the Northern Hemisphere grapes are harvested in September and October. After the grapes are picked, the vines begin to store carbohydrates in their roots and trunks in preparation for winter dormancy. When these stores are adequate, the grape leaves begin to change color. After the first frost they fall off the plant. The grapevines are now in a dormant stage until the new growth cycle begins again in spring.