The main pruning of grapevines is carried out in winter (much easier to manage the leafless stems). In early spring, the separately described shoot thinning follows, and after that (if required) the pinching back of shoot tips. Ideally, summer pruning simply means cutting off the ripe grapes. In vineyards, summer pruning - also called "green pruning" - has been minimised due to its labour intensity. However, for very vigorous vines, highly manicured espaliers, as well as for high quality table grapes, it may be necessary.
Vigorous young vines tend to produce shoots up to several metres long. During the training phase (i.e., in the first three years) this is acceptable, because an abundant biomass actually strengthens the vine. In the following years, such shoots may become a nuisance. Shortening them, however, encourages the growth of axillary shoots (Image 02), which may grow just as vigorously as the previously pruned shoots.
Axillary shoots from the leaf axils are usually only pruned if they are extremely long or as vigorous as the associated main shoot. During training, axillary shoots are not trimmed, because their carbon dioxide assimilation actually strengthens the plant.
Often summer pruning is carried out to achieve a very neat appearance of the grapevine espalier (Image 03). Vines without summer pruning are much bushier and grow further into the space away from the façade (Image 04). Summer pruning also reduces the workload for winter pruning, because the vine is already more manageable (Image 05).
An alternative to summer pruning may be to let all shoots grow fully and then, either partially or entirely, to change to rod pruning or cane pruning during the next winter pruning, which means that all that vigour can be transferred to the grapes. In later years, it will become easier to establish a balance between growth vigour and fruitfulness.
Summer pruning in the broader sense also includes "foliage thinning" around the grape zones in late summer. Single leaves covering the ripening grapes are removed; this is best done in 2-3 stages over 2 weeks-- never all at once due to risk of grape sunburn. Defoliation does not mean that the grapes will be sweeter, but they will colour better. The grapes will also dry faster after rain, preventing botrytis bunch rot (grey mold). However, when in doubt, foliage thinning should be omitted.