How to Increase the Size and Diameter of Table Grapes

Practice cluster thinning as a way to increase the size of individual grapes per cluster. Thinning may be done with flower clusters before bloom, or with fruit clusters after fruit set. Pinch off excess clusters, spacing the clusters you leave along the canes. Generally, the more flower clusters on a vine at bloom time, the smaller the size of individual grapes at maturity. Each variety of grape differs, so familiarize yourself with your specific vines.

Use a method of berry thinning to remove a portion of the individual grapes from clusters. Pinch off the lower portion of elongated clusters after fruit set. This technique gives the remaining grapes more room to grow. If you use a berry thinning technique, you can leave more clusters on the vines, because each cluster will be smaller.

Spray the grapes with gibberellic acid. GA is a compound that occurs naturally in gibberellins, or plant hormones. Seedless grape varieties often respond to treatments with GA with increased berry size. Results vary between grape varieties. Some varieties may develop larger grapes but suffer from a reduced number of grapes per cluster.

Girdle the vine or canes just after fruit set when the berries are 4 to 6 mm in size. Make the girdling cuts shallow and not more than one-eighth inch in width. Use a specialized girdling tool to guide the cuts to avoid damaging your vines.