When my husband pruned the vines, he pruned them down to the main trunk. A. Incorrect pruning will severely affect the crop set on grapes, says UC master gardener Bill Pierce. He recommends Sunset Western Garden Book for the best illustrations of pruning methods. All your grapes should be pruned using the cane method. Thompson Seedless grapes are naturally small.
Commercial growers girdle their vines to produce larger grapes.
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