Thinning grapevines increases ventilation and light to crops and also concentrates energy to the remaining bunches, so rather than a copious amount of sparse, small grapes you’re more likely to produce large, juicy clusters. Sometimes grapes can actually get too large so don’t be afraid to thin these too, as it will stop your vine becoming overcrowded. Take a clean, sharp pair of fruit snips to cut off clusters. When growing dessert grapes in a greenhouse it’s also necessary to remove individual grapes within a bunch, ideally cutting out one in three grapes to allow more space for the remaining fruit to grow.