Tuesday, January 14, 2014

Pruning for Table Grapes

Mary Beerman, Durham Master Gardeners

Pruning for grapes has a number of adaptations depending first on the grape selection, and second on the type of training the vine has undergone.

There are 3 basic types of grapes that can be grown: Vitis vinifera, European wine grapes and the ‘Thompson’ seedless, Vitis labrusca, which includes the hardier American hybrid grapes and Vitis rotundifolia, which includes the Muscadine grapes best suited for southern gardens. Carefully select a cultivar appropriate for your climate as well as for your training and pruning preference. Some cultivars are best suited to specific training and pruning.

Pruning grapes begins at planting; for most of us this can be in early spring or fall. It is best to first have your trellising, pergola or staking in place, however, temporary staking can be done for the first growing season. You will need to replace this staking with a permanent structure during dormancy in the first year (late fall-winter). In year 1 you prune to establish the trunk of the vine. At planting, cut your vine back to 2 -4 buds. Remove all other vegetative growth. In early spring of year 2 prune your vine back to 3 – 4 upward facing buds. When these have grown to approximately 8” long choose the healthiest shoot to serve as the trunk; pruning off all other shoots except for this one. This shoot is your ‘insurance’ shoot. It will serve as the ‘renewal spur’. Prune this shoot back to 1 or 2 buds. As the vine grows continue to remove any new side shoots appearing along the trunk. You can let leaves remain as important feeders to the trunk. Once the trunk cane grows just higher than the first, or preferred, trellis wire or the top of the pergola prune the cane tip and tie it to the support. This pruning action prevents the cane from growing taller and provides a point for attaching the vine. The pruning that follows will depend on the type of branching framework (training) preferred by the cultivar, the type of trellis structure you have chosen, your garden space and your climate.   
There are several ways to train your vine. The two general types of training: Cordon-Trained vines and Head-Pruned vines. Since pictures paint a thousand words review the diagrams below for an orientation to each type of training.

 For cordon-trained vines, after initial pruning, train two permanent lateral arms, or cordons, to grow along the wire in opposite directions.

For head-trained vines, prune the trunk to the top trellis wire. Choose five lateral shoots to grow from the head of the trunk, then train the arms along the wire.

Grapes fruit on one year canes. Annual and bi-annual pruning is required to maintain a productive vine. When you prune depends on how cold your winters are. In Ontario it is best to prune in early spring when the coldest of weather has passed. This timing will allow pruning wounds to heal and you will have the chance to remove any winter-kill. There are a few rules to follow for effective pruning:
  • Prune any shoots growing on wood older than 2 years.
  • Prune canes that are not fruit bearing.
  • Hand pull leaves around fruit clusters nearing harvest to allow for full sun exposure.
  • Prune canes that overwhelm the trellis.
  • Early-prune fruit cluster tips to force larger fruit and denser clusters.
  • Pruning can remove up to 90-95% of the vine growth each year.
There are two basic methods of pruning: Spur pruning and Cane pruning.  Note the diagrams below for direction.

For spur pruning vines, start with a cordon-pruned vine. Choose 6 to 8 spurs. Each year, remove the previous year’s growth and the cane furthest out on each spur, then cut back the remaining fruiting cane on each spur to 2 buds each.

For cane pruned vines, prune canes back to 8 -15 buds for fruiting every year and leave 2 bud spurs for next year’s harvest. 

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