When should grapevines be pruned, and how should they be pruned for the best results?
During the growth of grapes, besides basic water and fertilizer management, they also need to be pruned to promote tree vigor. Grape pruning can be divided into spring pruning, summer pruning and winter pruning, so when pruning, you must master the timing well. So when is the best time to prune grapevines? How should they be pruned?
Grapevine pruning time
Generally, winter pruning begins 2-3 weeks after the grapevines shed their leaves naturally. In the eastern, central and southern regions of Henan Province, grapevines do not need to be buried in soil for cold protection in winter, and winter pruning is mostly done in January. At this time, the organic nutrients in the grapevine have already transferred to the canes and roots, which can reduce the nutrient loss from winter-pruned branches to the lowest degree. In the northern regions of Henan Province (such as near Anyang, which is the boundary between regions in China where grapevines are buried in soil for cold protection and regions where they are not), freezing damage often occurs because low temperatures arrive early. To facilitate burying in soil for cold protection, pre-pruning can be done before burying (mid to late November), cutting away poorly matured slender weak branches and canes that do not need to be retained, and after they are unearthed in the following spring, a comprehensive pruning can be carried out once more.
Pruning methods:
1. Pruning of one-year-old branches: New shoots produced in the current year are called one-year-old branches after leaf fall, and in the following year they can produce vegetative new shoots (vegetative branches) or fruiting new shoots bearing clusters (fruiting branches). They can serve as extension branches to expand the trellis surface and as fruiting mother branches to arrange fruiting positions. According to the length retained at winter pruning, they are conventionally divided into: extremely short spurs (retain 1 bud), short spurs (2-3 buds), medium spurs (4-5 buds), long spurs (retain 6 buds or more), and super-long spurs (10 buds or more). Grape branches, especially one-year-old branches, are solid only at the diaphragm of the node. When pruning, the cut should be made at the diaphragm, which can protect the bud at the cut from damage caused by being too close to the wound, low temperature, drought and strong wind. In specific application, the following situations should be treated differently.
(1) Variety: Some varieties in the Eurasian group, such as Longyan, Beauty Finger, Crimson Seedless, etc., when used as fruiting mother branches, should be pruned mainly to medium and long spurs, and more buds should be retained on the mother branch when pruning; conversely, for varieties with weaker growth vigor, such as Muscat Hamburg, Victoria, Black Pinot, etc., the fruiting mother branches can be pruned with 1-2 fewer buds retained, mainly to short and medium spurs.
(2) Thickness and sturdiness of the branch: The ideal thickness of a fruiting mother branch should be 0.8-1.2 cm. It is not true that the thicker the branch, the better! This is because overly thick branches are often excessive in vegetative growth, and the buds growing on them develop somewhat poorly. Within the same variety, thicker and sturdier branches should retain more buds when pruned, whereas weaker branches should retain fewer buds.
(3) Position where the branch grows: When it is on the outer periphery of the trellis surface and there is room for development, it should be left long; if it is below the fruiting mother branch (position) and is used as a reserve branch in double-branch renewal, it must be left short. For fruiting mother branches on the upper part of a single hedgerow trellis surface, when there is no need to further expand the trellis surface, even sturdy branches should be left short, so as to prevent the fruiting position from rapidly moving upward. On perennial canes, branches sent out from latent buds are generally rather slender and weak. When cultivating them as fruiting positions, they should be short-pruned and retained (1-2 buds), so that they can turn from weak to strong.
(4) Summer and autumn weather conditions: Summer and autumn are important times for further differentiation of grape flower buds. If there is continuous cloudy weather and much rain, the node position at which flower buds form will rise. To ensure the yield of the second year, appropriate consideration should be given to retaining 1-2 more buds during winter pruning.
(5) Site conditions of the vineyard: In vineyards with thin soil and poor fertilizer and water conditions, fewer fruiting mother branches and buds should be retained appropriately during winter pruning; conversely, in vineyards with fertile soil and relatively complete comprehensive management, more mother branches can be retained and left long, but not too many and not too long, as excess will be counterproductive.
(6) Tree vigor: Generally speaking, strong trees can retain more and leave them long; conversely, weak trees should retain fewer and leave them short. However, grapes are a particularly sensitive tree species. For weak trees, as long as management is kind afterward, there will be a fairly good turnaround in the same year.
2. For perennial canes: Perennial canes are the framework of the grapevine. The cane tissue is relatively loose, and the branch cross-section shows that the pith accounts for a large proportion, and it is particularly sensitive to branch thinning. Continuous thinning of branches can easily weaken tree vigor, and especially for perennial canes, opposing wounds must be avoided! Grape pruning should grasp the principle of “better to block than to thin”. And the canes should be treated differently according to their growth conditions.
(1) Cane age: Young canes 1-2 years old have relatively vigorous growth vigor. To expand the trellis surface and increase fruiting positions, more branches and longer buds can be retained appropriately. For canes 5-6 years old, emphasis should be placed on using sturdy branches at the rear part of the cane for retraction and renewal, or using root suckers to cultivate new canes.
(2) Growth posture of the cane: On a single grapevine, upright-growing canes grow relatively vigorously, while horizontally growing canes are often moderate or weak. To balance the tree vigor of the whole vine, weak canes are often positioned upright to make them turn strong, while strong canes can have their angle increased to make them turn from strong to weak, thereby balancing the growth vigor of the whole vine.
(3) Distribution of mother branches on the cane: On perennial canes, if there are sturdy branches at the rear part, retraction can be used for renewal and rejuvenation. But in production, more often the cane still has relatively sturdy branches at the tip, while the lower or rear part of the cane has already become bare. For this kind of weak cane, the bare rear portion of the cane can be pressed into the soil to let it grow roots (increasing root mass). In winter, depending on the growth condition of the tree, it can be separated from the mother plant or retained and cultivated further.
(4) Cane thinning: Main canes that have clearly lost economic benefit and have declined and become bare should be thoroughly thinned out. When thinning canes, the saw cut should be below ground level, the cut should be smooth, and it can be leveled with a sharp knife, preferably coated with a protective agent.
3. Special points of grape pruning: Grapes are a vine fruit tree with a large annual growth volume and a love of light, but they do not have strong xylem, while the pith accounts for a very large proportion. This determines the differences between grape pruning and that of many other fruit trees. In short, there are 3 points, namely “the number of branches retained per unit trellis surface should be sparse rather than dense; pruning of branches and canes should be better to block than to thin; when pruning one-year-old branches, the cut should be made at the diaphragm above the node”.