Grape vines need to be trimmed during the dormant part of the growing season to generate new growth in the spring. Cutting back old canes and offshoots gives the grape vines a chance to concentrate on fruit production instead of vegetation growth. Pruning keeps the grapevines from becoming a jumbled mass of confusion and also keeps the vines healthy and productive.
Trim grapevines at the end of the harvest season when the fruits have been gathered and the leaves are turning brown. Locate the main trunk of the grape vines and cut back any new canes forming around the base. This is the perfect time to clear any debris that has gathered throughout the growing season.
Tie colored tape or cloth strips around each section of the grape vines. Use one color for older canes and another for this year's shoots. Mark old vines or shoots with a color which signifies removal.
Trim the grape vines so there are the desired number of cordons. Cordons are the lateral vines growing on the support system or trellis. The number of remaining cordons is determined by the support system. A fence-type system allows for two or four cordons to remain. An overhead trellis system allows for more cordons so the entire trellis is covered.
Inspect the fasteners holding the vines in place. Replace any that are worn and add new ones needed for new cordons. At this time, move the chosen cordons onto the support system and fasten them to the wires or wood.
Cut the ends of the cordons off so there are at least 10 to 15 shoots on each one. The shoots will grow next year and the buds on the shoots will produce the grape harvest.
Trim the shoots on the cordons so there are about 30 or 40 buds left. Trimming too much will force the grape vines to exert unnecessary energy in foliage production. Without a good supply of leaves for photosynthesis to occur, the grape production will suffer. Either the grapes will not ripen or the crop will be small.
Remove the trimmings and any dead or diseased vines. Check again to make sure the grape vines are fastened securely to the arbor or support system. Add mulch at this time to help protect the vines for winter.