Understanding trellis "anatomy" for cold climate grape establishment

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

 

Constructing a reliable trellis is a key step to successfully establishing a vineyard. Trellises come in various designs and there are multiple tools and supply options to choose from for construction and maintenance. The first step to simplify the initial planning process is understanding the function of each trellis feature, which will be broken down into six different sections for the purpose of this article. 

 

Why do grapes need to be trellised?

 

Trellises are the hardware onto which grapevines are trained. Left to their own devices, grapevines would grow bushy and become difficult to manage and harvest. Thus, a trellis provides the support needed to train both permanent and semi-permanent grapevine parts, such as a trunk and cordons, guide shoots, and uphold the crop weight of a fully ripened grapevine without collapsing. 

Trellis designs can vary, but they are typically built as either two-dimensional or three-dimensional. While three-dimensional trellises offer some added benefits for vigorous vines and fresh eating grapes, most wine grape growers use two-dimensional trellis designs. Two-dimensional systems also simplify some vineyard management tasks, including winter pruning. Overall, it can be helpful to remember that trellis form determines its function. 

Each trellis design sets up which training systems can be utilized. For example, a two-dimensional trellis can support bilateral cordon systems like Vertical Shoot Positioning (VSP), High Wire Cordon (HWC), Scott Henry, or Fan training. Alternatively, both Modified Munson and Geneva Double Curtain are examples of training systems for three-dimensional trellis designs. The diagram below is a simplified version of a two-dimensional trellis with wires set up to train VSP grapevines.

 

Trellis parts:

 

 

Image 1: A simplified two-dimensional grape trellis diagram for VSP trained grapevines with an anchor and brace wire; featuring 1) end posts, 2) end post brace, 3) line posts, 4) fruiting wire 5) training stakes, and 6) catch wires or single shoot training wires. Graphic created by Madeline Wimmer.

 

 

 

 

End posts bear a lot of force from the tension exerted by the fruiting and catch wires and the weight of the vines throughout the year. End posts can be installed into an augured hole or with an industrial post pounder most typically to a depth of 2-3 feet. The installation depth, post width, and angle will influence its sturdiness. The final post height should take into account installation depth and the anticipated grapevine canopy height. 

Materials: End posts are typically made from wood, but other material options, such as steel or reinforced concrete, are also available. Which material a grower chooses to use for an end post involves considering row length, with longer rows requiring sturdier, stronger posts. Additionally, soil type, management practices, and cost or availability of materials also influence which materials are suitable. For example, growers who manage their vineyard organically would avoid using treated wood.

 

 

The end post brace refers to the reinforcement strategy used to create counter tension on the end post. This prevents the end post from caving in on the ends from the internal weight of the trellis and wire tension. An anchor and brace wire is one approach to maintain counter-tension for the end post (refer to image 1).  

Materials: Anchors can be made from wood (i.e., tie back post) or metal like an earth anchor. Earth anchors vary in helix diameter and larger diameters are suitable for longer rows (e.g., 6in helix supports up to 600 ft rows1). Thicker wire or even a cable can be used in some circumstances to diagonally connect an anchoring feature to an end post.

Alternatives to using an anchor and brace wire include the H-brace (refer to image 2 below) or a slant brace (refer to image 4); however, these designs require more wood materials and can be more costly. The H-Brace additionally takes up more end space, which can be disadvantageous for vineyard blocks with short space for turning a tractor between rows.  

 

Image 2: A modified H-brace end design for a grape trellis. Graphic created by Madeline Wimmer.

 

 

 

 

Line posts, which are sometimes referred to as "in-line" posts, are positioned at regular intervals within the trellis row and reduce the total weight load. Without line posts, a trellis row would need to be much shorter in length to prevent sagging and potential collapse.  Growers typically install one line post every 21-28 feet of the inner trellis row. This allows for 3-4 grapevines per panel spaced between 6-7 feet apart. Keep in mind that vine spacing should be based on anticipated vigor based on soil conditions and cultivar type. 

Materials: Line post can be wooden, metal, or reinforced concrete.

 

 

Fruiting wire is where the grapevine cordons, spurs, and fruit-bearing shoots exist and it is the wire that bears the most weight. 

 Training wires should be installed through wooden end posts by guiding a wire into a drilled hole within an end post, guided along the trellis, into the second end post, and secured with a wirevise on the both trellis end post outer sides. For steel or other end post styles, the wires can be secured with a clip to maintain its position and then wrapped around and connected with a Gripple® connector or wire tensioner.

Materials: The fruiting wire is usually a single galvanized wire between 12-10 gauge, which is thicker, or a lower gauge, than what is used for catch wires. 

 

 

 

Training stakes are used to support the grapevine trunk as it establishes and should be as tall as the fruiting wire, or the anticipated vine height. In Image 1, shown above, its training stake would be appropriate for a VSP training system where the training wire is positioned at 3-4 feet, but for would need to be taller for HWC systems. 

Stakes provide the extra benefit of keeping trunks straight during training, which allows for more energy within the vine to be directed toward fruit production. 

Training stakes should be clipped to the training wire to keep them stable. 

Materials: Stakes can be made from wooden materials like bamboo, or metal, however, metal stakes will last longer. 

 

 

Catch wires and single wires are used in vertical shoot training systems including VSP and Guyot to guide shoots upwards each year. Catch wires are double wires that are secured around the end post outer side and connected by a wire tensioner or Gripple® connector.  

Catch wires offer the advantage of being able to tuck shoots, which can save time on shoot training; alternatively, single wires require a method to attach shoots to the wire, which can be done with a Tapener® tool. 

 

Image 3: A vineyard block with a two-dimensional trellis where three training systems are being implemented: 1) VSP 2) HWC and 3) Scott-Henry (SH). This trellis was constructed with all wooden posts and an H-Brace end post design. Readers should note that hosting multiple training systems on one trellis is possible, but not typical. This vineyard was designed this way for research purposes. 

 

What about apple trellises?

 

High density apple systems like tall spindle and super spindle are commonly trellised. Apple trellises are similar to grape trellises, but tend to be much taller and the training stakes are much stronger to support an apple tree's weight and growth. 

Similar to how bird netting can be drape over grape trellis rows, growers can utilize apple trellis systems to support overhead or draped hail netting. Recently, the University of Minnesota has looked into draped hail netting specifically, as a tactic to exclude insect pests and reduce pesticide use. To learn more about overhead and draped hail netting, visit our webpage "Hail netting for apple orchards."

 

Image 4: Apples trained on a high density trellis system using a slant brace to maintain counter tension on the end post. Photo taken near Rochester, MN, at ApplesRus Orchard. 

 

Publication: 

The Drummer and The Wright County Journal Press

PO Box 159
108 Central Ave.
Buffalo MN 55313

www.thedrummer.com

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