Do you want to grow the grapes for harvesting quality fruit? If so, when your vines are dormant, prune them to canes with spurs, removing 90-95 percent of the previous year's growth. Leaving the vines unpruned can result in a tangled mess that invites disease, looks untidy, and reduces the fruit quality. For a thorough guide to pruning and grape growing, read The Grape Grower by Lon Rombough. If your vine fails to cover the arbor the way you'd like with this type of pruning, prune the plants less. You'll sacrifice some fruit quality by doing so, however. Or grow your grapevine on a smaller arbor or trellis, cutting it back hard, and grow a nonfruiting vine, such as trumpet vine, sweet autumn clematis, or wisteria, on your arbor.