Answer: Grape vines don't generally require feeding; in fact too much fertilizer can cause rampant vine growth and very little fruit production. You can mulch the vines lightly with compost, to add some nutrients to the soil, but hold off on applying any commerically prepared fertilizer. Your grape clusters will mature if the season is long enough (the heat requirement depends upon the variety you're growing). To ensure sweetness at maturity, thin the clusters so there's only one or two per cane, which will help concentrate the plant's energy into just a few large clusters of grapes.
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