A popular and versatile fruit, grapes are eaten fresh, made into jelly, squeezed into juice, and fermented into wine. Many cultures throughout the world grow and enjoy grapes. Grapevines progress through five principal stages of annual growth. Each stage plays a crucial part in the process. The amount of time spent on each part of the growth cycle varies, depending on climate and the grape variety.
Bud break, the first stage of the grapevine's annual growth cycle, begins in spring. In the northern hemisphere, this occurs around the beginning of March. In the southern hemisphere, it begins around the beginning of September. Grapevines pruned in the winter "bleed" when temperatures exceed 50 degrees and the ground begins to warm. As the ground warms, water goes from the roots into the vine and flows out of the cuts. As the vine bleeds, buds appear. Leaves begin to emerge three or four weeks later. Treat powdery mildew, the greatest threat to grapevines at the bud stage, with anti-fungal sprays. Trim off extra shoots so all energy goes to flower development.
Approximately 10 weeks after buds appear, flower clusters manifest. Depending on climate and location. This generally occurs in May or June in the southern hemisphere, or 40 to 80 days after the buds appear. Optimal temperatures for the blooming of flowers range between 59 and 68 degrees Fahrenheit. During this stage, pollination and fertilization occur. Heavy rains and high heat reduce the likelihood of pollination. Decreased fertilization results in smaller grapes.
During the fruit set stage, the flowers begin to turn into grapes. Unfertilized flowers fall off the vine. Shelter the grapes during this stage from frost and cold night temperatures. Heavy watering in this stage results in plump grapes. Excessive sun during this stage results in sun-scald on the grapes. Shelter the grapes from intense sun during the fruit set stage.
Ripening, also known as veraison, occurs as the grapes begin to develop color and soften. The softening, caused by sugar accumulating in the grapes, leads to ripeness. Ripening occurs at different times; grapes exposed to more warmth ripen first. During this stage, the grape cells divide, which results in increase in the size of the grapes. During ripening, grapes grow in size, deepen in color, soften and become sweet.
Harvest time, the stage that makes all the work and waiting worthwhile, generally takes place approximately 100 days after the flowers develop. During this stage, wineries use grapes clipped off the vine to start the wine making process, growers ship them to stores for sale and consumption or they end up on the table of the home gardener.