Trellising Grapevines
Trellis Construction
Building a good vineyard trellis is very important not only because it is often the single largest cash expense in the establishment of a vineyard but also because it can significantly influence the long-term productivity and profitability of a vineyard. A wide range of materials can be used to construct vineyard trellises. The trellis structure is usually constructed with well-anchored, heavy wood end posts anchored by strong row-end braces. This allows the use of high-tensile wire that can be tightened firmly to support the weight of the vines in production. Interior support line (trellis) posts are usually smaller in diameter. The best time to construct a trellis is during the first growing season. Grapevines planted before trellis construction run the risk of being damaged by workers and equipment.
Line Posts
Line posts are a major cost component in the establishment of a new vineyard. The choice of line post materials will be influenced by the types of posts available, the post installation equipment, the vine training system, cost, and personal preference.
Wooded Posts from Native Tree Species
Posts cut from native tree species can be used (e.g., black locust, cedar, etc.) and can be expected to last up to twenty years or more. Posts cut from trees that are not rot-resistant will last no more than ten years.
Pressure Treated Wooden Posts
Wood line posts, which have been commercially injected under pressure with a preservative, are the predominant type of trellis post used in many vineyards today.
Metal Posts
Metal trellis posts are an attractive option too because they are relatively easy to handle and to install and their cost can be competitive with wood posts.
Trellis Wire
Trellis wires generally serve two functions. They are either load-bearing wires, which support most of the weight of the vines or used as catch wires, which help orient shoots. Many different types of wire have been used for vineyard trellising from traditional steel wire to high-tensile (HT) galvanized steel wire. High-tensile (HT) galvanized steel wire has a greater tensile strength in the range of 200,000 pounds per square inch or more.
Securing Wire to End Posts
Wires may be secured to end posts in various ways. If using just galvanized wire it can be wrapped around the post and twisted several times around as it is stretched to the next post.
Securing Wire to Line Posts
In the case of line posts, wires are fastened to the posts with ordinary galvanized staples or inserted in holes drilled in wood line posts. The staples must be driven deep enough to hold the wires close to post, but with enough play that the wire will slip through when tightening is needed.
End Posts and Anchorage
Regardless of the trellis system used strong row-end braces are critical to the strength of the trellis. The purpose of an end assembly is to provide an anchorage point for the wires. When constructing a trellis system, growers need to consider the height and weight of the vines, resistance to wind, the weight of fruit, and stresses from mechanical harvesting.
Inverted "V" End System
The inverted “V” end assembly is commonly used for high trellises (See Figure 8.1), which consists of a 9 foot (2.7 m) end post (4 ½ to 6 in, 10 to 15 cm diameter), set at approximately a 60 degree angle leaning way from the row rather than upright, and anchored with a screw-type steel anchor.
H-Brace End Assembly
The H-brace assembly (See Figure 8.2) is regarded as the strongest, as the design keeps the force on the vertical end posts, distributing it over a larger area. Two posts are set at least 6 to 10 feet (1.8 to 2.1 m) apart with a horizontal cross member placed at the top of the posts.
Tie-Back End Assembly
The tie-back end assembly (See Figure 8.3) is a system where the load is transferred through the end post to an anchor in the ground.
Mechanically Farmed Vineyards
In general, it is preferable to minimize the use of trellis systems and training configurations in a vineyard since mechanization is easier to implement and more cost-effective when fewer combinations are employed. If using different trellis or training systems it may require different implements, attachments, or adjustments, which will likely increase not only the number of implements required to farm mechanically but also the amount of time required to mount, adjust and maintain equipment.
Trellis Construction Costs
A vineyard trellis is often the single largest cash expense in the establishment of a vineyard. Not only does trellis construction impact on the economics of vineyard establishment but it also can significantly influence the long term productivity and profitability of a vineyard. As mentioned, a wide range of materials can be used to construct vineyard trellises. Too often little thought is given to the important characteristics of a vineyard trellis.
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