Dormant pruning is a critical component of the grape production system, providing the mechanism to maintain the training system, to select the fruiting wood, and to manipulate the potential quantity of fruit produced. Annual dormant pruning removes the previous year’s fruiting canes or spurs (now two years old) and excess one-year-old canes. The fruiting habit of grapevines dictates a pruning practice that encourages the annual development of new fruiting wood. Fruit is only produced on shoots growing from one-year-old canes. Therefore, healthy new canes must be produced every year to maintain annual production of fruit.
The training system is designed to encourage the production of new fruiting canes at specific positions on the vine - the arms. Pruning is used to selectively remove unsuitable or extraneous canes, retaining a small number of good canes. Canes are carefully selected to serve two functions: 1) produce fruitful shoots in the coming season, and 2) produce healthy shoots from which a good fruiting cane can be selected in the next dormant season. At each arm, these functions can be divided between two canes: a fruiting cane or fruiting spur, (depending on the training/pruning system) and a renewal spur. Alternatively, a single fruiting cane or spur can be used at each arm, and one of the basal fruitful shoots is subsequently retained as a fruiting cane for the next season.
Dormant pruning of grapevines can be done at any time between leaf drop in the fall to budbreak in the spring. However, the logistics of completing the job in a specific time period and the availability of labor often influence the timing of pruning. There also are vine health considerations that enter into the decision of when to prune. Pruning in the fall may increase vine susceptibility to freeze injury compared to later pruning (Wolf and Poling, 1995). Therefore, in regions where there is a significant risk of cold injury, it can be advantageous to postpone pruning until after winter’s coldest temperatures. Postponing pruning also enables an assessment of cold injury and adjustment of pruning levels to compensate for injury losses. Later pruning commonly causes the vines to “bleed” sap from the pruning cuts, but this is not harmful to the vine.
In addition to maintaining the vine’s training system, pruning reduces crop production by removing fruitful buds. Varying the extent of dormant pruning is one method to influence cropping level. The term bud count (also node count or node number) is used to describe the number of dormant buds retained at pruning. Generally, bud count considers only the buds having clearly defined internodes in both directions (Wolf and Poling, 1995), thus basal buds are not included in the count. Basal buds, sometimes referred to as noncount buds, are not included in bud counts because frequently they do not produce shoots, and if they produce a shoot it is often unfruitful.
Grape growers often prune vines with the intent to achieve a balance between fruit production and adequate, but not excessive, shoot growth. Increasing the bud count increases the number of shoots, which, if excessive, can lead to a crowded canopy and increased shading. Cropping levels are also increased when bud count increases, and the vine may not be capable of fully ripening high crop levels despite the increased shoot number. At very high bud counts the vine compensates for the large number of shoots with shorter shoot growth and fewer clusters per shoot (Coombe and Dry, 1992).
Excessive pruning - retaining too few buds - leads to an undercropping situation. Removal of fruitful buds reduces crop, but it also eliminates primary shoots. When there are too few shoots in relation to the vine’s growth capacity, the vine compensates for the deficit by stimulation of shoot growth from secondary, tertiary, or latent buds, increased vigor of shoots, and more extensive lateral shoot growth. The consequence is often an excessively shaded canopy that provides a poor fruit-ripening environment.
Because pruning directly influences the number of shoots and the potential crop level, it is often the most significant annual management practice affecting vine balance. Consequently, the concept of vine balance is the basis of most pruning strategies. In some winegrowing regions, balanced pruning formulas are used to guide growers’ decisions on the number of buds to retain. The bud count is based on an estimate of the weight of extraneous canes removed by pruning - the pruning weight. For example, the formula [20 + 10] indicates that 20 buds should be retained for the first pound of pruning weight and another 10 buds for each additional pound. Thus a vine with a 3-pound pruning weight would retain [20 + 10 + 10 = 40] buds. Wolf and Poling (1995) recommend a [20 + 20] pruning formula for Chardonnay, Riesling, Cabernet Sauvignon, and Cabernet Franc in the mid-Atlantic region of the United States. Balanced pruning formulas may not be reliable, however, when summer trimming of shoots is done as part of canopy management. Development of balanced pruning formulas requires pruning research on the specific varieties and growing conditions of a region, and such work has not been done in Texas.
Another pruning strategy that utilizes the vine balance concept is to adjust pruning levels based on a visual accounting and assessment of cane growth from buds retained in the previous year. A balanced vine will have strong, but not overvigorous, cane growth from all retained buds. If some canes are weak, correspondingly fewer buds should be retained for the next season. However, this may not fix the problem and other vineyard factors should be investigated as possible contributors to low vigor.
If some canes were excessively vigorous, that is an indication that the vine’s canopy may have been too large, perhaps because too few buds were retained the previous year. Again, other vineyard circumstances must also be considered, such as having vine spacing too close for the soil type or excessive application of fertilizer. The situation might be remedied by retaining a corresponding number of additional buds to accommodate the excess vigor, if there is adequate space on the trellis. If a crowded canopy is likely to be a problem, another solution will be necessary. See our webpage on
Canopy Management for recommendations on dealing with a crowded canopy.
Pruning Cuts. All pruning operations should be conducted with well-maintained, sharp pruning tools. Pruning cuts on canes or spurs should be made at least one inch beyond the last retained bud. For cane pruning, it is common to make the cut directly through the next node beyond the last retained bud. Cutting through the extra node prevents it from producing a shoot, but the enlarged nodal region helps keep the tying material from slipping off the end of the cane. Ideally, cuts should be made at approximately a 45 degree angle, preferably with the lower end of the cut angled away from the bud.
Cane Pruning. The first step in pruning is to identify the fruiting canes for next year. Desirable fruiting canes develop under conditions of good sunlight exposure, which is a function of the training system and last season’s pruning level, and canopy management practices. Good sunlight exposure promotes bud fertility and wood maturity. Fruiting canes and renewal spurs should be selected from positions close to the trunk head to prevent the arms from becoming too long, which will cause a nonproductive gap in the canopy above the head. The characteristics of desirable fruiting canes are:
- Firm wood with brown periderm nearly to the tip; a sufficient number of healthy, fruitful buds; and without mechanical damage or visible disease infections.
- Round in cross-section with relatively short internodes (3 to 4 inches) and moderate diameter (1/4 to ½ inch).
- Well positioned on the arm (i.e., arising close to the trunk).
Following selection of good fruiting canes (either one or two depending on the training system and vine spacing), another good, well-positioned cane is selected as a renewal spur and pruned back to one or two buds. Periodically, it may be useful to retain a watersprout (during shoot thinning) that is closer to the trunk than the current renewal spur. At the next dormant pruning, the watersprout cane becomes the renewal spur. This practice keeps arm length from becoming excessively long.
An alternate method does not retain a separate renewal spur. Instead, it is assumed that in the next dormant season, a good basal cane from last season’s fruiting cane can be selected as the new fruiting cane. The remainder of last year's fruiting wood and all other extraneous canes, including suckers and watersprouts, are removed. Suckers should be traced back to their source and cut back completely to remove all their basal buds. Fruiting canes are trimmed to a length that retains the desired number of dormant buds. The pruning cut is made through the next node (bud) beyond the retained buds, so that the enlarged portion of the node prevents the tie from slipping off. Next, all tendrils and laterals are removed, the cane is bent up onto the fruiting wire, wound once around it, and tied at the end.
Spur Pruning. Cordon-trained vines are typically spur-pruned. Just as with cane-pruning, the arm positions of cordons are established by the training process and all fruiting and renewal spurs arise from this area. The arms should be evenly spaced along the cordon, and oriented in the proper direction (up or down depending on the training system). Select suitable canes for the new fruiting spur and renewal spur using the same criteria described for cane pruning. Remove the old fruiting wood from the previous season. The selected fruiting cane is shortened to create a fruiting spur containing 2-4 buds, depending on the fruitfulness of basal buds and the desired cropping level. The renewal spur cane is cut back to one bud. Similar to cane-pruning, selection of canes for spurs should take into consideration the position of the cane on the arm. Select canes to maintain as compact an arm as possible and to maintain the desired spacing between arms.
Coombe, B.G. and P.R. Dry. 1992. Viticulture Volume 2 Practices. Winetitles. Adelaide, Australia.
Wolf, T.K. and E.B. Poling, 1995. The Mid-Atlantic Winegrape Grower’s Guide. North Carolina Cooperative Extension Service.