Grapes are a popular fruit for eating fresh or processing into jellies, jams, juice and wine. Grape vines are grown as ornamental plants or to create shades and screens. Well trained and grown grapevines can yield up to 9.07 Kilogram or more of grapes per year.
Grape vines are evergreen or deciduous and bear red, green or purple grapes. Understanding the life cycle of grape vines helps in procuring the maximum harvest from the grape vines.
Bud break is the first stage after the plants start coming out of their dormancy. Prune grapes during dormancy; this is critical for bud development. The newly appearing buds are susceptible to damage from frost and hence need to be protected. Dependent on specific weather conditions, the new leaves commonly appear three to four weeks after bud break. This is also the time when the vines maximise their food storage through photosynthesis. Grapevines are also prone to powdery mildew disease during this stage, which can be controlled with the use of antifungal sprays. The plants can also show extra shoot growth and these have to be removed so as to maximise the energy for the optimal development of flowers.
The vines start to develop flower clusters within about 10 weeks of the initial bud break. This is usually in May or early June. The period of flowering is determined by the grape variety and the weather conditions in the area. This is also the time for the pollination of the flowers, which is necessary for the formation of the fruit. Very hot temperatures and heavy rain can impede good pollination. It only takes a week or two for the flowers to get pollinated and if the weather is not right during this period it results in a smaller sized fruit.
In the fruit set stage, the pollinated or fertilised flowers start to turn into grapes and the flowers that were not pollinated drop off the tree. Young fruit needs to be protected from night chills or any frosts in the area. The grapevines need heavy watering at this stage to prevent the berries from drying out. The fruit cells undergo division in this stage and continue to get larger. Thin shoots and leaves on the vines frequently to create ample space to accommodate the growing grapes. Protect the fruits from bright and direct sun at this stage as this can cause sun scald.
Veraison refers to the colouring of the grapes and the stage is characterised by the colour development in the fruit and their softening. The softening of the fruit is the result of the accumulated sugars in the grapes and can also be considered the ripening stage. The colour of the grapes is directly determined by the variety. In order to produce a good colour many growers lift the canopy or shade from the vines at this stage. Veraison continues till late July and then tapers off.
The last stage comprises of harvesting the mature grapes. Again the final maturity time of the grapes is dependent upon variety. Generally the period of maturity is reached about 100 days after the development of flowers. The grapes are first tested for sugar and acid levels before they are harvested. The life cycle of the grapevines ends in the fall and the plants start to recede into dormancy and their leaves start to fall off. Pruning is critical during dormancy as this protects the plants from periods of extreme frost.