Summer pruning is a management practice performed on grapevines during the active growing season, unlike the dormant pruning done in winter. This technique involves selectively removing vegetative growth, such as leaves and shoots, to regulate the vine’s canopy after the fruit has set. The objective of this mid-season maintenance is to manage the vine’s energy resources and optimize the environment surrounding the developing grape clusters. By manipulating the foliage, growers aim to achieve a balanced vine capable of producing a high-quality harvest.
Why Summer Pruning is Necessary
The primary benefit of summer pruning is redirecting the vine’s energy (photosynthates) toward the developing fruit, a process known as sink activity. Controlling excessive shoot growth allows the vine to focus carbohydrate production on fruit maturation rather than producing unnecessary leaves and stems. This diversion of resources supports the clusters, resulting in improved fruit size and sugar accumulation.
Reducing canopy density also increases sunlight exposure to the fruit clusters. Direct sun exposure is necessary for synthesizing compounds like anthocyanins, which develop color in red grape varieties. An open canopy ensures that the leaves, the main site of photosynthesis, are well-exposed to light, maintaining the vine’s health and productivity.
Controlling foliage density is also a powerful tool for disease prevention. A dense, shaded canopy traps humidity, creating an ideal microclimate for fungal pathogens like powdery mildew and Botrytis bunch rot. Increasing air circulation by removing excess leaves and shoots promotes faster drying after rain or dew, significantly reducing the risk of infection.
Timing and Essential Preparations
Summer pruning must be carefully timed to coincide with specific stages of vine development. Shoot thinning and removal of unwanted growth should begin early in the season, typically when shoots are tender and can be easily snapped by hand. Intensive canopy management, such as leaf removal, is generally performed immediately after fruit set, once berries reach a pea-sized stage.
Pruning should occur before the fruit begins veraison (final ripening) to allow berries to acclimate gradually to increased sun exposure. Use sharp, clean hand pruners for cuts involving older, lignified wood to ensure a clean wound and minimize disease risk. Avoid pruning during periods of extreme heat or drought stress, as the vine may struggle to recover from the loss of foliage.
Specific Techniques for Canopy Control
Shoot Tipping/Topping
Shoot tipping halts the lengthwise growth of main shoots, which often grow vigorously and consume vine energy. This involves removing the actively growing terminal end of the shoot (the apical meristem). Removing this tip stops shoot elongation and encourages the vine to divert energy into the fruit clusters.
The cut is typically made one to five leaves beyond the last visible fruit cluster. Cutting here ensures enough mature leaves remain to provide sufficient photosynthesis to ripen the fruit. This action also helps establish a uniform canopy height, making vineyard management easier and preventing rows from shading one another.
Lateral Removal (Suckering)
Lateral shoots emerge from the leaf axils along the main shoot. Suckering refers to removing non-fruiting shoots that arise from the trunk or base of the vine, which are unproductive and waste resources. The removal of these laterals and suckers is best done early in the season while they are young and can be rubbed off easily.
Removing laterals within the fruit zone (the area surrounding the grape clusters) is especially helpful for improving the microclimate. Laterals positioned higher in the canopy can be retained or tipped, as they contribute to the leaf surface area needed for energy production. Judicious removal improves light penetration and airflow without significantly reducing the vine’s photosynthetic capacity.
Leaf Removal (Leaf Pulling)
Leaf removal is the targeted removal of basal leaves directly surrounding the fruit clusters. This practice is effective in exposing the grapes to light and air, which is the key mechanism for disease reduction and color enhancement. The most common timing is post-fruit set when the berries are small and less susceptible to sunburn, but before the canopy becomes fully dense.
The goal is to remove approximately two to five leaves from the shoot near the clusters. This is usually sufficient to achieve the desired microclimate changes without overexposing the fruit to intense sun, which can cause scorching. It is important to leave substantial foliage higher up on the shoot, as mature leaves are the primary producers of sugars required for fruit ripening and winter wood development.