A grape trellis functions as a support system to manage the vine’s growth pattern. This structure elevates the fruit-bearing canopy away from the ground, which is fundamental for maintaining plant health. Proper trellising ensures that the leaves and developing fruit receive maximum sunlight exposure, directly influencing sugar development and flavor complexity.
Elevating the canopy promotes superior air circulation, which helps to reduce humidity around the leaves and fruit clusters. This improved airflow limits the conditions favorable for fungal diseases, such as powdery mildew, which can compromise the entire harvest. Ultimately, a well-built trellis simplifies vineyard management, making pruning and harvesting tasks more efficient and productive.
Selecting the Right Trellis Design
The configuration of the trellis structure influences how the vine canopy develops and the amount of fruit it can support. For many home growers, the choice balances the vine’s natural vigor with the available planting space. A common system is the Vertical Shoot Positioned (VSP) trellis, which manages the vine’s growth within a narrow, upright plane.
The VSP system uses multiple parallel wires stacked vertically, typically spaced 12 to 18 inches apart, to contain the shoots and maximize light interception on both sides of the row. This design is suitable for varieties with moderate growth habits and is preferred in smaller spaces where row width is limited.
Alternatively, a High Wire or T-bar system encourages a broader, horizontal canopy spread. The High Wire design utilizes a single wire positioned higher, often five to six feet, to train the permanent cordons, with the shoots allowed to hang down naturally. This arrangement is suited for grapes with high vegetative vigor, providing greater exposure and air movement across a wider area. Deciding between a narrow vertical structure or a broad horizontal system depends entirely on the specific grape cultivar chosen and the dimensions of the site.
Gathering Necessary Materials and Tools
Building a sturdy trellis requires materials that can withstand weight, exposure, and wire tension. For the upright supports, use pressure-treated wood posts (often 4×4 lumber) or galvanized steel posts to resist decay and ensure longevity. End posts bear the full weight and tension of the line; they should be larger (typically 5 to 6 inches in diameter) and set deeper than the intermediate line posts.
The wires must be high-tensile, galvanized steel wire (usually 9- or 12.5-gauge) to resist stretching and corrosion. A specialized tensioning system, such as in-line wire tighteners or ratchet-style strainers, is necessary for maintaining tautness. This hardware allows for seasonal adjustments, compensating for temperature-induced wire expansion and contraction.
Tools
Tools required include:
- A post-hole digger or auger for setting the posts.
- A sledgehammer or post driver.
- A level to ensure all posts are plumb.
- Measuring tapes and wire cutters.
- A crimping tool for securing the wire ends.
Step-by-Step Trellis Construction
The initial phase involves site layout to ensure the rows are straight. Begin by determining the desired length of the row and marking the location of the end posts, followed by the intermediate line posts, which should be spaced approximately 16 to 24 feet apart to distribute the load. Stretching a string line tautly between the two end points provides a visual guide that guarantees the alignment of all subsequent posts.
Once the locations are marked, the end posts must be secured first. These posts require setting deep into the soil, generally to a depth of at least three feet, and must be braced either externally with an anchor cable or internally with a diagonal wooden brace. Without sufficient support, the strain applied when the wires are tightened will cause the end posts to lean inward, compromising the structure.
Following the end posts, the intermediate line posts can be set, typically to a depth of about two feet, ensuring they are vertical using a level. These posts do not require bracing but serve to hold the wires at the correct height and prevent them from sagging under the weight of the canopy and fruit. With all posts set, the hardware needed for holding and adjusting the wires can be installed on the end posts.
This hardware includes eyebolts or metal brackets to attach the wires, along with the in-line tensioning devices. The tensioners should be positioned near the end posts for easy access when adjustments are required. A common VSP system requires running three to four parallel wires, with the lowest wire positioned about 30 inches above the soil, marking the point where the permanent trunk and cordons will be trained.
The high-tensile wire is then strung from one end post to the other, passing through staples or pre-drilled holes in the line posts. Leave enough slack initially to connect the wire ends to the tensioning hardware. Once secured, the wire is gradually tightened using the strainers until it is taut, firm enough to support the future load. The correct tension ensures the canopy remains open and the structure can withstand wind and ice loads.
Training the Grapevine onto the Structure
The completed trellis is functional once the young grapevine is integrated with the framework. The initial step in training involves selecting the strongest shoot emerging from the base of the newly planted vine. This single shoot will be designated as the permanent trunk, and all other competing shoots should be removed to focus the plant’s energy into this vertical growth.
The selected trunk is then secured to the nearest upright post or the lowest trellis wire using material such as biodegradable twine or nursery tape. The attachment point should be loose enough to prevent girdling the growing stem but firm enough to hold the shoot vertically. This initial connection directs the vine’s growth upward, preventing it from sprawling along the ground and initiating the formation of the straight, permanent trunk.
As the trunk grows, it must be secured to the wire or post at intervals of 10 to 12 inches to maintain its vertical posture. The goal is to encourage the trunk to reach the height of the lowest permanent wire, where the vine will begin to develop its horizontal arms, or cordons. Establishing this vertical alignment early ensures the future fruit zone is correctly positioned for efficient light interception and management.