In a cane-trained system, new canes are laid down each season. Grapevines under this system are generally head-trained at the top wire. New shoots that are produced during the growing season harden-off as canes with a reddish-brown color and will be approximately pencil size in diameter. Two of these canes are selected and tied down to the top wire; one cane is laid down in each direction. Canes can be tied using pieces of cloth, twist ties or plastic stretch tape.
Buds are counted and the number is adjusted according to the desired fruit load. Cordon-trained systems are different in that new spurs are established each growing season as one-year-old canes and are pruned back to three to four buds per spur. When growing grapevines on an arbor, the fruiting wood may be either one-year-old canes or spurs that are attached to cordons positioned on top of the arbor.
Pruning practices vary a great deal based on the type of grapes grown. American and French-American hybrid varieties are more commonly grown in home gardens than Vinifera varieties since they are more winter hardy and disease resistant. Vinifera varieties tend to be grown by more advanced grape gardeners.
American, French-American hybrid, and Vinifera varieties differ in the amount of fruiting wood that is produced annually. American cultivars tend to have the greatest amount of vegetative growth followed by French-American hybrid varieties. Vinifera varieties have the least amount of foliage. The amount of one-year-old wood to be left after pruning is dependent on the amount of vegetation produced during the previous growing season.
For example, a vine that has three pounds of wood pruned off will have 30 buds left for the first pound and 10 buds left for each of the second and third pounds of wood. A total of 50 buds will be retained. If more than 3 pounds of wood were produced in the previous growing season, additional buds would need to be retained to help balance the crop load.
A grapevine will over-compensate with increased foliage if there is not a proper amount of fruit load to store carbohydrates produced in the leaves. If the appropriate number of clusters is left on a grapevine, there should not be a lot of excess foliage produced.
As Figure 2 shows, a non-combed vine will have several one-year-old canes trailing in different directions. In Figure 3, the combed vine is much neater, easier to prune, and will produce better fruit and canes. All one-year-old canes that grew along the cordon will be pruned back to either three- to five-node spurs as fruiting wood or one-node renewal spurs as vegetative wood. The cut end of the spur should measure at least pencil size in diameter.
Grapevines are normally considered to be mature and fully productive in year three. In our climate conditions, too often the upper level shoots are so vigorous that they shade out the lower level, so the kniffen system is not much used. The third method sometimes used is the cordon system. Some wine grape varieties produce better when trained to this method, though it is not recommended for American types such as Concord. In the second season, one cane is trained to each side of the trunk, and they become permanent arms that remain as the base on which short spurs are established to produce new fruiting canes each year.
These spurs are two or three buds long. In pruning a cordon-trained vine, it is sometimes necessary to cut back old spurs that have grown too long. Select the cane that is closest to the cordon arm, cut it to two buds, and remove the rest of the old spur. In many areas with deep soils and high nitrogen content, grape vines are very vigorous and produce too many shoots.
Even when vines are not too vigorous, some shoot thinning is usually needed to take out unproductive shoots with no fruit clusters, or those that are too closely spaced. This is called canopy management. The aim is to balance the productivity of the vine and the amount of leaf and shoot growth. Each grape shoot needs 14 to 16 well exposed leaves to properly ripen a grape cluster. If too many shoots are crowded together, the leaves do not get enough light for effective photosynthesis.
Thinning grape shoots in the early stages eliminates shoots that are unproductive and provides light and space for the productive ones. Training and tying the shoots upward on the trellis wires should also begin fairly early , to maintain spacing and keep the shoots from trailing on the ground or breaking off in the wind.
Plastic grape clips are good for this and last for years, or a Max Tapener of the kind used for tying up tomato plants. Later in the season, if shoots are long and vigorous, with more than 14 — 16 active leaves, shoots can be topped or cut back on the ends to prevent shading the lower vine. Also, new shoots may emerge where a leaf joins the main shoot. These side shoots should be removed.
Dr Peter May is one of Australia's leading horticulturalists and he has been growing grapes as a hobby for 25 years. He prunes the vines every year as part of routine management. It's important to prune young vines. Start when the vines are one year old vine because that will set it up for the following season. This involves pruning off all growth except for one shoot, which should be cut back to just two buds and then that lets it grow a nice straight trunk for next season.
Peter said that the mistake most people made when training young vines was to not prune them enough in the first season. A vine, in its second year, was pruned back hard last winter and has already grown a nice straight shoot up to the training wire.
To prune this, look for wood that's about as thick as a pencil and prune off everything else. When the vine reaches its third year, it's time to prune it as a mature or proper grapevine. Peter said this involved looking for two canes that would carry a reasonable crop the next season and two replacement spurs.
Peter looks for a couple of shoots that are within about a hand span of the training wire. Two will be cut short and the other canes will be left longer. The canes are then wrapped around the wire. But wrap these in the reverse direction. Some spurs are left to replace the fruiting canes next season.
Every time the vine is pruned a self replicating pattern is set up. This keeps the vine productive and ensures the fruit crop is close to the trunk," Peter said.
This is where a permanent branch is set up on the trellis wire - so two arms are trained along the horizontal wires or the frame of a pergola.
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