Left untended, an old grapevine becomes a tangled mass of branches. As a result, the grapes become hard to pick and diseases fester in the darkness.
Pruning brings such a plant to manageable size and coaxes it to bear large crops.
The first goal in taming a neglected grapevine with pruning shears is to create a trunk.
Of the many stems arising at or near the ground, choose one healthy, vertical branch for the new trunk. Cut away all other shoots originating at or near ground level.
Next, select canes growing off this new trunk. Canes are 1-year-old stems, and they give rise to fruit-bearing shoots. Canes are easily recognized by their smooth, tan bark in contrast to the dark and peeling bark of older wood.
Mark with a ribbon four canes originating near the trunk. Choose two growing horizontally in opposite directions from a height of about 5 feet and two growing horizontally in opposite directions from a height of about 3 feet.
Now select another four stems originating near the trunk, two each at about the same height as the canes. Shorten each of these stems to two buds long. These are renewal spurs that furnish buds that grow into fruiting canes for next year.
Selecting renewal spurs near the trunk each year keeps fruiting canes always originating near the trunk.
The next step may seem overly brutal, but it's not. Remove all growth except for the trunk and the renewal spurs and canes you marked with ribbons. Much of the remaining growth on the plant probably is long and tangled, so remove branches in pieces. After you cut each piece, give it a sharp jerk to release it from clinging tendrils, then slide it free.
Finally, shorten the four fruiting canes that remain on the plant. This will channel energy--and flavor--into fewer bunches. Leave about 10 buds on each cane (not counting the buds clustered closely together at the base of a cane), or about 40 buds per plant. Leave more buds on very vigorous vines, less on weak vines. Twist the shortened canes around a trellis wire or tie them loosely to some support.
And never let your grapevine fall into neglect again. To keep the vine manageable, fruitful and healthy, each winter select and shorten new fruiting canes, leave renewal spurs and remove all other wood except for the trunk.