Answer: There are several reasons for grapevines producing small grapes. In order, they include young plants unable to maintain growth and produce fruits simultaneously, not enough water during fruit maturation, over-fertilization, cool summer temperatures, or a short growing season. Thompson's seedless are borderline for your growing region, but they are capable of producing delicious grapes. If your grapevine is young (less that 5 years), give it some time to mature. You can increase the size of the fruit it sets by thinning the grape clusters. The fewer clusters it has to mature, the better the grapes will be on the clusters that remain. Provide ample water during the summer months, but hold off on the fertilizer. Too much nitrogen will result in lots of vegetative growth, at the expense of flowering and fruit. Best wishes with your grapevines!
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