Trellising is a fundamental practice in viticulture that provides the necessary physical framework for the vine. A well-designed trellis supports the plant’s vigorous growth, keeping fruit and foliage off the ground. This system manages the canopy (the collective mass of leaves and shoots) to maximize sunlight exposure for efficient photosynthesis and sugar production. Trellising also significantly improves air circulation around the clusters and foliage, which helps minimize the risk of fungal diseases such as powdery mildew and botrytis.
Choosing the Best Trellis Design
Selecting the appropriate trellis system depends on the grape variety’s natural growth pattern and the space available. Grapevines are categorized by their growth habit: upright growth (like most Vitis vinifera) or downward/trailing habit (common in American and hybrid varieties). The chosen design must align with the vine’s natural tendencies to ensure productivity and ease of management.
The Vertical Shoot Positioned (VSP) system is a popular choice for upright-growing cultivars, particularly where space is limited. This system trains the shoots to grow vertically, creating a narrow, hedge-like canopy between sets of catch wires. The fruiting zone is typically positioned low, around 36 inches from the ground, with the foliage managed above it. The VSP system is effective in cooler climates because it ensures excellent light penetration and air movement, promoting even ripening and reducing disease pressure.
The High-Wire Cordon system is better suited for highly vigorous, cold-hardy varieties that exhibit a trailing growth habit. In this configuration, the permanent cordon (arms of the vine) is established higher up, typically 60 to 72 inches above the ground. The new shoots and fruit hang down like a curtain from this high wire. This design is simple to install and requires less intensive daily canopy management than a VSP system, as the shoots naturally drape downward.
For growers prioritizing aesthetics or shade over maximum yield, an Arbor or Pergola offers a decorative solution. This system uses an overhead frame, often over a patio or walkway, allowing the vines to spread horizontally across the top. While it provides a beautiful, shaded retreat and can produce fruit, the horizontal structure can make canopy management and disease control more challenging compared to row-based wire systems. This option is best for single-vine installations where the primary goal is ornamental rather than high production.
Essential Materials and Site Planning
Before construction begins, the site must be prepared and the necessary components gathered, focusing on durability and strength to support the heavy weight of a mature vine and its fruit. End posts, which bear the majority of the tension, should be robust (4×4 or 6×6 inches in diameter and 8 to 10 feet long). These posts, whether pressure-treated wood or durable metal, must be anchored securely.
Intermediate line posts support the wires between the end posts. They can be lighter, typically 7 to 8 feet long, and are usually spaced 20 to 30 feet apart along the row. For the wires, a high-tensile, galvanized steel wire in the 9- to 12-gauge range is recommended for strength and corrosion resistance. The fruiting wire must be the heaviest gauge to support the weight of the crop.
Anchoring hardware is necessary to prevent the tensioned end posts from being pulled inward by the wires. Growers commonly use deadmen (buried wood or concrete blocks) or screw-in earth anchors, secured with cable or heavy wire. Tensioning devices, such as turnbuckles or ratchet-style wire strainers, are also needed at the end posts to allow for seasonal tightening of the wires.
Constructing the Trellis Structure
Construction focuses on creating a stable, high-tension framework, beginning with the placement of the end posts. These posts should be set deep into the ground (ideally 3 to 4 feet) and angled slightly outward to counteract the pull of the tensioned wire. An anchor system is then installed, connecting the top of the angled end post to a buried anchor point, which provides the necessary resistance.
Once the end posts are secured, the intermediate line posts are placed along the row, typically set 2 feet deep into the ground, and aligned with a string line to ensure a straight row. These posts are generally spaced to correspond with the planting location of each grapevine. The next step involves attaching the wire hardware, such as eye bolts or J-hooks, to the end posts at the designated wire heights (e.g., 36 to 40 inches for the fruiting wire).
The high-tensile wire is then strung between the end posts, passing through the line posts, often secured with staples or clips that allow some movement. Tensioning the wire is a separate operation, using the turnbuckles or strainers attached at the end posts. The wire should be pulled taut enough to resist significant sag under the crop’s weight, but not so tight that it stresses the posts and causes failure.
Training Young Vines Onto the System
Training a young grapevine begins immediately after planting, with the primary goal of establishing a strong, straight trunk. In the first year, only the strongest shoot is allowed to grow; all other developing shoots should be removed so the plant directs energy into vertical development and root establishment. This selected shoot is loosely tied to a temporary stake or the lowest trellis wire to encourage its upright path.
As the main shoot grows, it is continually guided upward toward the intended height of the permanent cordon wire (3 to 6 feet high). Once the shoot reaches just above the permanent wire, the tip is pinched off. This encourages the development of lateral buds below the cut. This topping action defines the head of the vine, the point from which the permanent arms will grow.
Two lateral shoots are then selected from these newly developed buds, one on each side of the trunk, and trained horizontally along the permanent fruiting wire. These two shoots will become the permanent cordons or arms of the vine, forming the structure that will bear the fruit. Any flowers or fruit clusters that appear during the vine’s first two years should be removed. This ensures the plant’s energy is focused entirely on establishing a robust root system and the permanent woody structure.