Trellising is a fundamental practice in viticulture that provides physical support for grapevines, allowing them to produce quality fruit. Without a structured support system, the vine’s sprawling growth habit leads to dense, shaded foliage and fruit clusters lying on the ground, increasing the risk of disease. A properly built trellis manages the vine’s canopy, ensuring optimal light exposure for photosynthesis and maintaining good air circulation. By keeping the fruit elevated and the canopy organized, trellising contributes directly to higher yields and improved fruit ripening.
Selecting the Appropriate Trellis System
The choice of a trellis system is determined by the grape variety’s growth habit, the local climate, and the available space. Two common designs are the Vertical Shoot Positioning (VSP) system and the High-Cordon system.
Vertical Shoot Positioning (VSP)
The VSP system trains the vine’s shoots upward into a narrow, vertical curtain, effective for Vitis vinifera varieties that naturally grow upright. This design uses a static cordon wire about three feet from the ground, with pairs of movable “catch wires” above it to hold the foliage upright. VSP is often preferred in cooler climates because it maximizes sunlight penetration into the fruiting zone and facilitates the management of dense canopies. The organized and accessible fruit clusters simplify tasks such as harvesting and spraying.
High-Cordon System
The High-Cordon system is simpler to construct and suitable for robust, high-vigor varieties, such as American and French-American hybrids, that exhibit a downward growth tendency. In this setup, a single, strong wire is typically placed between four and six feet high. The permanent wood (cordon) is trained horizontally along this wire, and the fruiting shoots and clusters are allowed to hang down below it. This system requires less seasonal labor for shoot positioning and effectively manages the heavy fruit load produced by vigorous cultivars.
Building the Trellis Structure
The trellis structure must be robust enough to support the weight of a mature vine, its crop, and withstand environmental factors like high winds and snow. The end posts are the most substantial components. They should be eight to ten feet long with a diameter of four inches or more, buried two to three feet deep to provide a secure anchor. These posts bear the entire tension of the wires and require strong bracing, such as an H-brace assembly, to prevent leaning inward under load.
Smaller line posts, typically seven to eight feet long, are installed between the end posts to support the wires along the row, usually spaced 20 to 24 feet apart. While wooden posts are common, metal posts are a durable alternative that is easier to install. The wire itself should be durable, galvanized, or high-tensile steel, with a gauge of 9, 10, or 11 standard for the main load-bearing cordon wire.
Wire tension is achieved using specialized devices like turnbuckles or ratchet-style tensioners attached to the end posts. These devices allow for seasonal tightening of the wire as the structure settles and the crop weight increases. Wires are secured to the line posts using staples. Staples should be driven loosely enough to allow the wire to move for tensioning, but firmly enough to keep it positioned. The specific height and number of wires depend on the chosen training system.
Training and Pruning the Grape Vine
Training a young grapevine begins immediately after planting, aiming to establish a strong, straight trunk up to the main cordon wire height. At planting, the vine should be pruned back to the most vigorous cane, leaving only two buds. The resulting single shoot is then tied loosely to a temporary training stake. All secondary shoots must be removed throughout the first growing season to direct all vigor into the main trunk.
Once the trunk reaches the main trellis wire, pinch off the growing tip. This encourages two lateral shoots to develop, which are trained horizontally along the wire to form the permanent arms, or cordons. The permanent cordon is distinct from the fruiting wood, which consists of one-year-old canes responsible for the current season’s fruit production. Grapevines produce fruit exclusively on shoots that emerge from buds established on the previous year’s growth.
Annual dormant pruning, performed in late winter or early spring, is necessary to regulate the vine’s fruit load and maintain the established trellis form. The two main methods are spur pruning and cane pruning.
Spur Pruning
Spur pruning involves keeping the permanent cordon and shortening the one-year-old canes growing from it. These are reduced to small, two-to-three-bud spurs spaced six to ten inches apart.
Cane Pruning
Cane pruning involves removing nearly the entire one-year-old cane. Only one or two long canes (with 10-15 buds) are left, along with a small, two-bud renewal spur for next year’s growth. Throughout the growing season, new shoots must be secured to the wires using flexible ties to ensure the canopy remains open and organized.