Should I Thin My Grape Vine Clusters?

Function

• Two primary reasons to consider thinning out grape clusters on a healthy productive vine are to maintain the strength of the vine or to improve the size and quality of remaining grape clusters. Trellised vines can snap or pull off support if the weight of grape clusters is unusually heavy or unbalanced. Fewer grape clusters allows plants to reallocate energy to fewer grapes for optimal development.

Considerations

• Some varieties of grapes known to be overly productive are best thinned out, according to Ohio State University's website. Examples of varieties that produce higher quality grapes from cluster thinning include: Seyval, Chancellor, Vidal and Chambourcin. Many grape vine varieties produce ample fruit of good quality without any thinning.

Time Frame

• Experienced grape growers familiar with the seasonal events and fruit development have two opportunities to thin out grape clusters. The first is in late spring when flower clusters appear because since you can see clusters more easily with smaller leaves. The other thinning time is once fruits are developing. A drawback to waiting to thin is that you are removing fruits already developing; flower cluster removal allows remaining clusters to grow with more flavor, sweetness and size for a longer part of the growing season.