Summer pruning of grapevines is an essential follow-up to winter pruning, typically carried out from May to August when the plants are in their most vigorous growth phase. This process is usually done 4 to 5 times throughout the season. The main goal of summer pruning is to balance the plant’s growth with fruit production, manage apical dominance, reduce unnecessary energy consumption, enhance air circulation and light penetration, and ultimately improve fruit development and flower bud formation. Here are some key aspects of summer pruning:
At the time of bud break, early shoots should be removed, especially in areas prone to late frost, where this can be delayed by 15 to 20 days. Bud thinning involves removing dense branches, side shoots, and any non-productive shoots that emerge on the trunk, main vines, or at the base. This helps minimize nutrient waste and promotes better growth.
Shoots are typically pruned when they reach a length of 10 to 20 cm, allowing for visibility of the inflorescence. In a trellis system, about 6 to 10 shoots per square meter are maintained, while in a framework system, around 20 to 25 shoots per square meter are kept.
When tendrils grow to 30 to 40 cm, their tips should be guided onto the support structure to prevent them from being damaged by wind or heavy fruit. As new shoots elongate, the vines need to be tied 2 to 4 times, while the fruit-bearing shoots should be tied 1 to 2 times.
Tendrils that wrap around the branches not only hinder plant growth but also consume valuable nutrients. Therefore, they should be removed as soon as possible.
Pinching the shoot tips, along with removing auxiliary shoots, can enhance flowering and increase fruit set. The ideal time for top pruning is when the flower clusters begin to spread out. For example, leave 10 to 12 leaves from the base upward, which means leaving 7 leaves above the top cluster. For nutrient management, it's recommended to leave 10 leaves before pinching.
Auxiliary shoots, which are vegetative buds that sprout and produce new vines, compete for nutrients and can lead to overcrowding. Unless there are empty spaces, all such shoots should be removed. Except for the last top shoot, one leaf should be left to avoid forcing the dormant buds to sprout prematurely. Additional removal of secondary shoots should be done several times during the season.
For varieties like Rosette and Kyoho, the spike length should be reduced to about 1/4 to 1/5 of the tip length 3 to 5 days before flowering. For long-spiked varieties, the spikes should be removed. At the same time, due to excessive branching and earing, too many small flower clusters should be thinned out to concentrate the plant's energy on the best ones, resulting in larger fruits.
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