Summer Pruning & Thinning of Grapevines

When winter pruning backyard grapevines, we generally leave 40 to 60 buds per plant, but this does not mean they will only have 40 to 60 shoots when they grow in the summer. If the cultivar you are growing is not adapted to your region, it's possible you will lose some buds due to low winter temperatures and have fewer shoots. More likely, however, is that you will have an abundance of shoots.

Figure 1 Grapevine trunk the needs to be suckered.
Figure 1: Grapevine trunk that needs to be suckered.

Suckering

Early summer is a great time to remove excess shoots because you can do most of it by hand, without the use of pruners. The removal of shoots on the trunk of a grapevine is generally referred to as suckering. The shoots on the trunk (suckers) often will not have fruit and will end up being shaded out (Figure 1) from the grapevine canopy above it. All the suckers should be removed in early summer unless you need to leave one to replace a trunk.

Shoot Thinning

Shoot thinning in the canopy is important as often grapevines produce more shoots than is ideal. Generally, we want to leave around 4 to 6 shoots per foot vine. If our plants are taking up about 8 feet of trellis, that means we want to leave around 40 to 50 shoots on them. In Figure 2 are shoots that were removed from the same vine on the same day. The shoot on the left is vigorous, has long tendrils, and large flower clusters. As you move to the shoots on the right, they are less vigorous, lack tendrils (or have small ones), and have fewer and smaller clusters. When shoot thinning in the grapevine canopy, our goal is to remove the shoots that do not have much fruit or are low in vigor. 

Shoot thinning should be done in early summer when the shoots are small and can be removed by hand. An additional benefit to shoot thinning early in the summer is that it increases the amount of sunlight that gets into the middle of the grapevine canopy (Figures 3 and 4). This sunlight is not only important for fruit ripening, but it also helps the grapevine buds to potentially become more cold hardy for the winter and have more fruit on them in the following season.

 

Learn more about growing grapes in this publication: Growing Grapes in the Home Garden

Figure 2 Shoots on the left are more desirable than those on the right.
Figure 2: Shoots on the left are more desirable and should remain on the plant.  Those on the right should be thinned out.

Figure 3 Under the grapevine view before shoot thinning.
Figure 3: Under the grapevine view before shoot thinning.

Figure 3 Under the grapevine view after shoot thinning.
Figure 4: Under the grapevine view after shoot thinning.

Category: 
Authors: 

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on June 17, 2022. The information contained within may not be the most current and accurate depending on when it is accessed.