Legend has it that Saint Martin’s donkey inadvertently gnawed at some vine canes and thereby invented pruning. Whatever its origins, pruning is one task no wine grower can ignore.
Vines are climbers
Left to its own devices, the vine, like all plants, searches for light. Armed with its little ‘fingers’ (tendrils), it clings to trees and quickly climbs up their trunks. In some places like Japan and northern Portugal for Vinho Verde, vines are still grown this way. But fruit set only occurs on the upper, youngest branches because flowers need to be displayed to pollinating insects for reproduction purposes – the same is subsequently true of the fruit so that birds can carry away the seeds. At the vine’s base and middle levels, there is no fruit. Despite this, they still use energy for sap.
A constant supply of quality grapes
If wine growers want to keep vines to a manageable size, they need to cut them back regularly. To ensure a permanent supply of grapes, the old wood needs to be pruned every time which has the added bonus of producing tastier, sweeter fruit. This is because the plant’s energy is not dispersed into the now-removed middle levels and can be used to form sugar in the clusters. Depending on the region, wine growers choose to train vines with stakes or leave them as they are. Metal wires pulled tight between posts are the most common ways of training vines but there are also single stakes, known as ‘échalas’ in the northern Rhone, and pergolas. Some methods do not use stakes at all and leave the vine stock as they are.
Below 12°C, sap stops rising and vines then enter a dormancy phase. Wood removal is therefore less traumatic to the plant. Armed with a secateur, often electric, wine growers prune one vine at a time, removing up to 70% of the plant. This technical task is often carried out in challenging conditions. It can usually be conducted from November – when all the leaves have dropped – to March. But the later the pruning, the later the vine will start shooting again and the less chance there is of it being affected by spring frosts. A lot of pruning therefore occurs in February, just when the weather is particularly chilling.
After the flowers have turned into fruit, the vine continues to grow. The upper branches serve no purpose at all. In fact, they absorb energy so that it can no longer go to the grapes, hide the fruit from the sunshine they need to ripen and can potentially collapse on the ground, thereby contaminating the plant with harmful fungi. Wine growers therefore trim the vines to remove them. Winter pruning, which is complicated, is nearly always done by hand whereas trimming trellised vines can easily be carried out by tractor.