Growing Grapes in Your Backyard
|Topic||How do I thin clusters and berries?|
Cluster thinning is used on table grapes to increase berry size, on wine grapes to reduce the crop size to improve wine quality, and on any weaker vines to prevent overcropping and stunting of the vines. Berries of raisin grapes do not need to be large, so cluster and berry thinning are not necessary. All clusters from vines with poor growth should be removed; otherwise thin in proportion to the vigor of the vines.
Healthy table grape vines often produce two or three clusters per shoot, and a typical strategy is to leave only one cluster per shoot. To ensure healthy vine development, in early spring pinch off any clusters that form in the first growing season. In the second growing season, remove all clusters again if vine growth was poor to moderate the previous year. If vine growth was strong in the first year, you can remove all but one cluster per two shoots. From the third year on, remove all but one cluster per shoot in April before flowering.
Clusters usually have broad shoulders and are thin toward the bottom. Another thinning strategy is to remove the lower one-fourth to one-third of each cluster by cutting the rachis at this point. This practice, called berry thinning, produces clusters that are more globular (like those sold in stores) with bigger berries.