Grapes should be pruned yearly because fruits only form on buds that arise from the previous season’s growth. There are various methods of training grapevines. Your preferences, space limitations, and the variety of grape you are growing will determine your trellis system.
Prune vines when they are dormant; in most of the country, that means very early spring, before any green shoots appear. In the south, grapes can be pruned any time.