John Wall, author of How to Build Orchard and Vineyard Trellises, explains the key components of a strong orchard support system. Photo: Tara Baugher, Penn State
John Wall, founder of John Wall Inc., and Bonita Whalen of Kencove Farm Fence Supplies, Inc. spoke with over 70 growers at the Fruit Research and Extension Center in Biglerville on January 29 in a workshop sponsored by the Young Grower Alliance (YGA). John and Bonita provided growers with quality insight into everything trellis system related and troubleshot questions ranging from proper stapling technique to material quality.
Mr. Wall was born in New Zealand and introduced high tensile smooth wire into the United States for trellises and fencing. At the time, high tensile wire was commonly used in New Zealand fences, but its introduction was novel in the US. John's company holds more than 13 patents, such as a fence post insulator for electric fences and a joining buckle for coated wire. He has also put together a construction manual on orchard and vineyard trellis systems specifications, one that is considered the "go-to" manual for trellis engineering. His highly popular Horsecote/Kencote product, while designed primarily for horses, is seeing good results for use in trellising cherries and peaches.
Trellis System Considerations
Factors to consider that lead to the success, or failure, of a trellis system include:
- soil type
- potential wind forces
- tree canopy type
These three aspects of your site will determine the material needs, post depth, and in-line spacing. Remember that larger diameter posts are stronger than smaller posts.
End posts are relatively standard: pressure treated wood, 5-6" in diameter, driven 4' into the ground. The length of the posts depends on the desired height of your trees. These posts should be hydraulically driven to help prevent pullout. A hydraulically driven post is 7 times stronger than a hand set post. In-line posts should be 4-5" in diameter and driven 3' deep. They should be a maximum of 30' apart; closer on rolling terrain.
End Brace Assemblies
Construction of a single-span brace assembly is outlined in John's book, and these are recommended for most types of high tensile wire trellises. These require a 4" brace post, an 8'x4" horizontal brace, and a 5" end post. The brace post and end post should be driven 4' deep, with post length determined by the desired tree height. With shorter tree rows, tie-back posts are an option. Tie-back posts should be 5-6" in diameter and driven 4' deep. Tie-backs need to be angled slightly away from the direction of the pull of your system.
Wire Tensile Strength and Resistance to Corrosion
Wire should be high tensile, class 3, 12.5 gauge, .099" galvanized steel wire. 12.5 gauge wire is more cost effective than other gauges of wire. Your wires should be 2-2.5' apart, allowing leaders to be fastened securely. Wire tension should be between 200-250 pounds per strand. However, over-tensioning your wires will weaken them. High tensile wire has greater breaking strength than other potential trellis wires. Because of this higher breaking strength, high tensile wire can be pulled tighter and provide greater support across the entire trellis system. Furthermore, high tensile wire is resistant to corrosion. Corroded wire is another potential source of failure.
According to John, "loose or sagging wires … serve as starting points for stretching and breaking - and ultimate failure of the trellis." Wires should be secured to the posts using 2 inch, 8 gauge, double barbed, class 3 galvanized staples.
Stapling to Resist Pull-Out
Staples should be placed so that they are at a 45 degree angle from vertical. Vertical staples are likely to separate the wood grain of your post and weaken your trellis. Also, the staples should be driven so that the legs of the staples spread outward. This makes them much less likely to be pulled out. According to John, "laboratory tests show that staples driven so that each leg curves away from the vertical centerline of the post have 40% more pull-out resistance than staples driven incorrectly (so that their legs converge)." While you can run wire through holes drilled in your posts, this is not recommended. Without proper airflow (a 3/8" hole is required per wire per post), the wire may corrode much more quickly than it otherwise would.
Joining of the wire can be done by use of crimping sleeves and a crimping tool for full strength connections. Other options on the market would be Fastlocks, Gripples, or Quick Splices.
Penn State Extension has developed a great tool that allows you to use Microsoft Excel to estimate costs for trellis construction. You can change variables such as number of wires and length of system, and the workbook will auto-calculate the cost of that theoretical system. Trellis Construction Workbook
There is also a video on trellis construction that is available in Spanish and English . Your local Extension Educators are great resources and will help to provide you with answers for any questions or concerns you may have about your trellis.