Grapevines get a hefty pruning every winter. In the first years, pruning is done exclusively for training purposes. During this process, a main framework with side shoots / branches 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 will follow. The information below will help you to determine the most suitable training form.
Before winter pruning, the vine ideally has a solid main structure with many long, woody (often intertwining) shoots from the past year. Many of these are cut away completely; others will be kept but substantially shortened and assigned to one of the following categories:
Fruiting 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 correspond to the different lengths (short, medium, long) to which these fruiting canes are pruned. Usually a combination of all three pruning methods will be used in the life of a grapevine.
Replacement canes ("replacement spurs"): These shoots are chosen to develop healthy and strong wood that will become fruiting canes and bear fruit after the following winter; that is, in two years. They also serve to re-establish the shape/training system of the vine or save the vine in the case of frost damage.
Canes for the Framework: Some shoots will be used to develop the vine framework~ to enlarge it / extend an arm / continue training to cover a larger area, etc..
Winter pruning is a major determinant of yeild- that is, how much fruit the vine will produce the following summer. As a general rule of thumb: leave 10 - 20 eyes (buds) per m2, and no more! For a vine framework covering 10 m2 of a facade, the vine should be pruned so that after pruning, all fruiting canes - spurs, rods and canes - have a combined total of about 150 buds.
The resulting 150 shoots --> canes will each produce 1 - 2 grape bunches the following year, although you can count on a few of them not making it. You can expect about 150 clusters weighing 200 g each (depending on varieties, this could even be 500 g and more). In total, this amounts to about 30 kg or 4 "water buckets" for the 10 m2, or about 3 kg per m2. If the grapes are to be pressed, the yield should be around 1.5 to 2 kg / m2. On freestanding espaliers in the vineyard, usually only about 1 kg / m2 is kept to achieve a higher sugar content.
Winter pruning can take place throughout the entire leafless period, though 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. Rough pruning- i.e., the cutting back of old stems, branches, or entire cordons, can be done as early as December to encourage the cuts to seal/callus and to prevent excessive bleeding in spring.