For many home gardeners, pruning grapevines is often a difficult, confusing chore. Fortunately, an understanding of the growth and fruiting characteristics of the grapevine should help simplify the pruning process.
Grapevines produce fruit clusters on the previous season’s growth. Before pruning, a grapevine may have 200 to 300 buds capable of producing fruit. If the vine is not pruned, the number of grape clusters would be excessive and the grapevine would be unable to ripen the large crop or produce adequate vegetative growth.
The purpose of pruning is to obtain maximum yields of high quality grapes and to allow adequate vegetative growth for the following season.
The most desirable time to prune grapevines is late winter or early spring. In Iowa, pruning can begin in late February and should be completed by early April. Grapevines pruned at this time of year may “bleed” heavily. However, the loss of sap will not harm the vines.
To maximize crop yields, grapevines are trained to a specific system. The most common training system used by home gardeners is the four-cane Kniffin system. The four-cane Kniffin system is popular because of its simplicity. In a four-cane Kniffin system, the canes of the grapevine grow on two wires, one located 3 feet above the ground and the second 6 feet high.
If using the four-cane Kniffin system, select four canes on the upper wire, two going in each direction. Also, select four canes on the lower wire. To aid identification, some gardeners tie brightly colored ribbons or strips of cloth on those canes they wish to retain. All remaining one-year-old canes should be completely removed.
Going back to the upper wire, select two of the remaining four canes (one going in each direction). Prune these canes back to one or two buds. These short one or two bud canes are referred to as renewal spurs. The renewal spurs provide the shoots or canes that will produce next year’s crop. Prune the remaining two canes on the upper wire back to eight to thirteen buds. The number of buds left on the fruiting canes is determined by plant vigor. If the grapevine is vigorous, leave thirteen buds per cane. Leave only eight buds per cane if the grapevine possesses poor vigor.
Prune the four canes on the lower wire the same as those on the upper wire. When pruning is complete, no more than 60 buds should remain on the grapevine. When counting the number of buds on the grapevine, include both the buds on the fruiting canes and those on the renewal spurs.
Tools required to prune grapevines include a hand shears, lopping shears, and saw. Brightly colored ribbons or cloth strips can be used to identify fruiting canes and renewal spurs.
For most home gardeners, pruning grapevines should be relatively easy with a basic understanding of pruning principles, the right tools, and a little courage. Additional information on pruning grapevines can be found in Pruning Grapevines (RG 502) and Growing Grapes in the Home Garden (PM 1707). Both publications can be obtained at your Iowa State University (ISU) Extension county office or the ISU Extension Online Store at www.extension.iastate.edu/store.