Introduction
Homeowners grow grapes for a variety of reasons, some of which include fruit production, landscaping, erosion control, privacy screens and shade. Vines are often used to cover walls, fences, arbors and various types of trellises. Each situation may require unique training and pruning as compared to growing grapes for fruit production only. However, the basic rules of training and pruning apply in all cases.
Grapevine Growth
Understanding how grapes grow helps gardeners train and prune properly. A number of terms are used to describe the grape vine (Figure 1). SHOOTS are the new green growth consisting of stems, leaves, tendrils and flower and fruit clusters that develop from previously dormant BUDS located on CANES. Plants less than two years old are often entirely vegetative with no flower or fruit clusters. CANES are the matured tan colored stems of shoots after leaf fall. They contain the dormant buds from which the next seasons shoots emerge. As buds are developed almost exclusively on new wood, canes become unproductive the second year, but suppor the next generation of canes and buds. SPURS are canes pruned back to one to three buds. BRANCHES/ARMS/CORDONS are laterals from the trunk consisting of wood two or more years old. Fruiting canes become branches in their second year. NODES are the thickened portion of the shoots/canes where the leaves and lateral buds are located.
Pruning Systems
The two systems of pruning are the cane and spur methods. In the spur system, canes are pruned to two or three buds in length to accommodate European grape varieties which fruit best from the buds near the base of each cane. The cane system is used for pruning American varieties which produce more from buds near the middle of their canes, consequently they are pruned to 6 to 12 buds each. The total number of buds reserved on each plant should be about the same for either system. The spur system may have up to 20 spur canes located along permanent branches (cordons), while the cane system commonly has only 4 to 6 canes. Often home gardeners use a combination of these pruning methods when maximum fruiting is not an overriding objective.
Training Systems
The two common training methods are the head and cordon systems. The head system develops fruiting canes and renewal spurs near the trunk on very short branches (arms). In the cordon system, the spurs develop on long branches (cordons) that extend four to five feet laterally along trellis wires.
Southern Nevada Conditions
Although many varieties of grapes grow well in this area, gardeners can expect plant stress from heat, drought, wind and high light. Some varieties may grow normally but slower than others. Infrequently, late spring frosts kill tender buds and reduce yields. Seldom is the vine killed outright. Winter dieback may occur from desiccation when vines are young. If the trunk of younger plants is killed during winter, suckers will resprout from the roots in spring. These suckers are the same as the mother plant except when the plant is grafted on a root stock. Any sprouting from below a graft does not make a desirable replacement plant.
Depending upon the grape variety, site and climatic conditions, fast growing plants may develop a trunk with lateral canes during the second year. These canes can then produce shoots and some fruit during the third season. A year's setback may occur with winter kill. Maximum fruit production usually occurs after the fifth or sixth year. Where late springs frosts are common or expected, delay pruning until just before spring bud break. This timing facilitates selection of viable canes and maintains plant twigginess that helps protect buds from mild spring frosts
Training And Pruning
High light in southern Nevada along with drying winds and droughty soils may cause leaves and fruits to sunburn if not protected. It is recommended that vines be trained to a trellis without spreading arms. A fence works well. Training grapes along a wire suspended from a cross arm on a fence or trellis exposes the leaves and fruits to more light and drying winds. Tender leaves and fruits sunburn. Otherwise, the outer leaves shade and protect inner leaves and fruit from the direct sun. Interestingly, grape fruits do not require direct sunlight to ripen. Do not spread the canopy out or much of the fruit will be damaged under southern Nevada conditions.
Illustrations may show only half of the plant and are drawn without leaves to reflect the dormant stage. The following discussion encompasses three objectives of training and pruning: fruit production, landscape beautification and managing older untrained vines.
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