Grapevines are rigorously pruned every winter. In the first years, pruning is done exclusively for training purposes. During this process, a main framework with side shoot positions is developed, whereby the shoots are pruned in the same way every year, either to spurs or rods for beginners, or to canes for the pros. No matter whether you purchase a fully trained grapevine, or have to train it first - you need to know which training form it follows or should follow. Reading this overview will help you to determine the most suitable training form. In summary: first the training, then each year the appropriate winter pruning!
Before winter pruning, the vine ideally has a solid main structure/framework, from which a vast quantity of long and often entangled shoots from the previous year arise. Many of these are completely cut off; others can remain but are shortened rigorously and allocated to one of the following categories:
Fruit canes: These canes are selected to produce fruit in the upcoming growing season. The three pruning methods mentioned above as "spurs," "rods," and "canes" relate to these fruiting canes and differ in terms of the length to which these fruiting canes are pruned. Often the pruning methods are used in combination.
Replacement canes: These shoots are selected to produce predominantly strong wood in the upcoming growing season. These will become fruiting canes only after the following winter, or they may be used to re-establish the vine after severe frost damage.
Stem wood: Many shoots are used for future stem extension, for continued training, and to develop the vine in order to cover more area.
The winter pruning determines significantly how much fruit the vine will produce in the following summer. As a general rule of thumb, it is best to leave 10 - 20 eyes (buds) per square metre, but no more! For a wall space of 10 sqm, the vine is pruned so that after pruning, all fruiting canes - spurs, rods and canes - have a combined total of approx. 150 buds.
The resulting 150 canes will each produce 1 - 2 grape bunches in the following year, although a few will fail. You can expect about 150 clusters weighing 200g each (depending on varieties, this could even be 500g and more). In total this amounts to about 30kg or 4 "water buckets" for the 10 square metres, or about 3kg per sqm. If the grapes are to be pressed, the yield should be around 1.5 to 2kg / sqm. On freestanding espaliers in the vineyard, usually only about 1kg / sqm is kept in order to achieve a higher sugar content.
Winter pruning can take place throughout the entire leafless period. However, in many regions pruning is not carried out in temperatures below -5 degrees C. The more sensitive the variety and the frostier the climate, the later the pruning should be done, sometimes well into March. Any frost damage can also be better corrected after severe winters.
Pre-pruning- i.e., the cutting back of old side shoots or entire stems- can be done in December to encourage the cuts to seal/callus and lignify and to prevent excessive bleeding in spring.