Grapevines produce fruit clusters on the previous season's growth. Before pruning, a grapevine may have 500+ buds, all capable of producing fruit. If the vine is not pruned, the number of grape clusters would be excessive. This will lead to small, poorly filled clusters that will not ripen at high sugar levels.
The purpose of pruning is to obtain maximum yields of high-quality grapes and allow adequate vegetative growth for the following season.
When to Prune
The best time to prune grapevines is in late winter or early spring. In the Midwest, pruning can begin in January and should be completed by early April before the buds swell. Grapevines pruned in the spring can bleed sap heavily, but this generally will not harm the vine. Pruning after bud swell can damage the remaining tender buds as the pruned items are pulled out of the canopy.
Grapevine Terminology
- Shoot: current seasons growth; green actively growing stems; may or may not have clusters on them (Figure 1)
- Cane: one-year-old wood that was a shoot last year, smooth bark (Figures 1 & 2)
- Node: compound bud on canes (Figure 1)
- Arm: perennial wood from off the cordon; rough bark (Figure 2)
- Cordon: horizontal perennial wood that is attached to wires; arms, canes, and shoots can originate from a cordon; rough bark (Figure 2)
- Trunk: vertical perennial wood that originates from the ground and is attached to the cordon; rough bark (Figure 2)
Pruning Tools
Personal preference often dictates which tools are used for pruning grapevines (Figure 3). Bypass pruners are limited to pruning thinner materials such as canes and small arms. Bypass loppers can be used for all pruning cuts except those on thick cordons and trunks. Saws are generally only used for cordons and trunks that are too thick for a bypass pruner or lopper.
Recommended Training System for Home Gardeners
The high wire cordon (HWC) training system is amenable to many different cultivars and is straightforward to maintain. In this system the cordon is on a wire at 5-6 feet tall and is trained horizontally. Canes that originate near the cordon are pruned to a few buds, and shoots are oriented downward. This ensures the fruit is high in the canopy, where it is more likely to be exposed to sunlight when shoots are oriented downward (Figures 2 & 4).
Pruning Concepts
Recommended Size of Vines After Pruning
Most grapevines in the Midwest should have around 6 to 8 feet of cordon. Grapevines will perform best when there are 4 to 6 shoots per foot of cordon. For a vine with an 8-foot cordon, that roughly correlates to leaving 40 to 50 buds on each vine after pruning. If cold temperature injury has occurred, you can leave some additional buds to compensate.
The retained canes can be cut to varying lengths, but generally leaving 3 nodes on each cane is a good approach. For an 8-foot cordon vine that we want to leave 50 nodes on, that would mean we need to leave around 16 three-node canes per vine. These canes should be even spaced on the cordon, when possible.
Selecting Fruiting Canes
Dark colored canes (Figure 5) tend to be more cold hardy and fruitful. Some varieties naturally have lighter or darker colored canes, so select the darkest canes for the vine you are pruning. Not all portions of grapevine shoots harden off as canes. Canes with significant dieback (Figure 6) should be completely removed since the dead portions will not have live buds.
Learn more about this process in these videos: Grapevine Pruning & Determining Winter Damage on Grapevines.
How to Make a Pruning Cut on Grapevines
When making pruning cuts on old wood leave a stub of around twice the diameter of the cut. This allows natural desiccation of the pruning wound to occur without negatively impacting the remaining portions of the vine. Pruned-off canes should be completely removed. Retained canes should be cut roughly halfway between nodes to avoid damaging the node near the cut. When canes of equal quality exist, attempt to keep those that originate closer to the cordon.
Pruning Examples
Figure 7 shows a two-foot section of a cordon, with the vine parts labeled. To achieve 6 shoots per foot of cordon, we should leave around 12 nodes in this section.
Pruning cut examples for leaving 4 three-node canes are in Figure 8. In area A, only one cane is dark in color, so it is removed halfway between the 3rd and 4th node. In area B, both canes are dark in color; however, selecting canes that originate closer to the cordon will keep the fruit higher up in the canopy. Prune the arm off in area B, leaving a stub, and cut the remaining cane between the 3rd and 4th node. Area C has 4 dark-colored canes, so remove the arm, leaving the closest cane to the cordon, and shorten the remaining cane to 3 nodes. In area D is a cane originating directly off the cordon. Shorten this cane to 3 nodes and we have our desired 12 nodes in the two-foot area of cordon.
Vines generally have over 90% of their growth removed annually (Figure 9). After dormant pruning, the remaining canes should be roughly evenly spaced on the cordon when possible. If a large gap between retained canes exists, try to leave a one-node renewal spur so pruning options can exist in the following season.
Follow-up Tasks
After pruning loosely tie the cordon to the trellis wires with twine. Check to make sure any twine from a previous year is not girdling the plant. Remove all pruned-off vine materials from the site since they can harbor disease.
