URBANA — "Proper pruning of grapevines is very important in managing plant size, shape, and productivity," said University of Illinois Extension local foods systems and small farms educator Maurice Ogutu. "Unpruned grapevines tend to have a lot of vegetative growth and produce less fruit."
Grapes are usually pruned when the plants are still dormant, from late February through March. Ogutu said pruning grapevines can be done using inexpensive hand tools such as hand shears for cutting smaller shoots. Lopping shears can be used to prune larger shoots and vines, and a pruning saw can be used when needed.
According to Ogutu, "It is very important to know the fruiting habits of grapes. Grapevines produce fruits on the previous season's growth. The canes that are the size of a pencil are selected, as they produce good quality fruits. The canes with diameters larger than a pencil tend to be vegetative and produce less fruit. The vines that are two years old or more tend to be more vegetative and less fruitful."
Grapevines can be cane-pruned or spur- pruned depending on how the plants are trained and the desired shape of the vines. Cane-pruning is done by selecting fruiting canes every year. The selected canes are cut back to leave the desired number of buds. Most of the grapevines trained in Kniffen System, where there is one main trunk with two or four fruiting canes referred to as "arms" arising from the trunk, are cane-pruned.
Grapevines on the Kniffen System are trained on one or two wires running between posts. The grapes are pruned by leaving two to four new fruiting canes per vine every year. The other canes are removed, including the ones that bore fruits the previous year.
Selected canes are cut back to leave 10- 15 buds per cane, based on the desired fruit load. The pruned cane is tied on the wire trellis using twine, pieces of cloth, or plastic tape. Short stubby canes with two buds, referred to as renewal spurs, are left closer to the trunk near each of the selected fruiting canes. The fruiting cane for the following year will be selected from one of the canes that will grow from the two buds. "Spur-pruning is done by selecting shoots, referred to as spurs, along the arm or main canes," said Ogutu. "They arise from the trunk and are trained on a wire trellis so the spurs appear as feathers arising from the cane."
"The new spurs are established each season as one-year-old shoots that are pruned back to three to four buds per spur during the dormant season. The fruit is borne on canes from the previous year's growth. This is the type of pruning done on grapevines on an arbor or trained in a Cordon System."