Grapevine Annual Cycle
The winter months are an important part of the California table grape growing cycle. Growth and development stop temporarily and the vine rests. This stage is called “dormancy.” At this time, growers prune the vine and set it up for the upcoming cycle to begin. Pruning and training of the vine are two of the most important aspects for quality grape production – growers decide how much and which parts of the previous season's growth to remove in order to regulate vegetative growth (shoots and leaves) and crop load (grape clusters) to produce quality grapes and optimum yield.
In early spring tiny buds on the vine start to swell and green leaves appear. Appearance of the first green leaves through the bud scales is called budbreak. Growth is slow at first. As the mean temperature rises, growth and shoot elongation accelerate. After three or four weeks, the period of most rapid growth begins – where shoots can grow an average of 1 inch or more per day. As the days warm up, flowers bloom, then shatter to make way for the tiny green grapes that will eventually ripen into clusters. Berry size increases rapidly. Sunlight and warm temperatures are vital to the physiological functions of the grapevine (such as photosynthesis).
The point in the growing season when ripening grapes begin to soften is called “veraison.” During ripening, colored varieties gradually change color from green to either red or black, while green varieties become translucent. Sugars start to accumulate in the berries. The interval from veraison to harvest is different for each variety. Unlike many fresh fruits, grapes are harvested fully ripe. After they're picked, they do not become sweeter, so timing is everything.