Vertical Axis Support System
These comments made at the High Density Tree School - 1997, on construction techniques for vertical axis support structures. Major contributors include Hugh W. Fraser, Agricultural Engineer, OMAFRA & Darryl Oakes, Lynoaken Orchards, Lyndonville NY.
POSTS - Pressure treated (CCA) pine is the preferred post to use. This species is stronger than cedar and will last longer. Cedar can not be effectively pressure treated because the cell structure is closed. All posts should be put into undisturbed ground. Posts that are pounded in are 50% stronger in resisting overturning than augured posts. For every 33% increase in depth the overturning resistance increases by 100%. Clay soils have more resistance than sand soils. Dry soil is better than wet soil. The big end goes down on augured holes; with the small end down when driven in. If inferior posts are used the trellis may fail prematurely costing valuable trees, fruit and more money. Poor anchorage is a common problem if growers are not careful. A quality post can last for 2 decades or the life of the planting. Resetting of posts may be necessary . A frost can heave a post a few centimeters each year after being pounded into the soil.
Vertical Axis Fig. - 1 - Dead head ANCHOR POST - 5 ft long by 5 - 6 inches in diameter, not sharpened, pounded 4 ft straight down in undisturbed soil. The grape industry uses a 5 ft. screw in anchor that works well. In the last few years, auger anchors have become standard in the apple industry. An auger anchor is essentially a large rod with a screw-like plate at one end. It is turned into the ground mechanically.
Vertical Axis Fig. - 2 - GRIPPLE (patented wire fastener) used to join wire and eliminate the need for an additional mechanical wire tightener on the wire as it can be retightened if needed. If a ratchet type of mechanical winching device or tightener is used, it should be placed in the middle of the wire length. Other mechanical tighteners that bend the wire excessively can break the wire. Retightening or changing wire tension with the season is not commonly done. A wire vise is a small locking device not much larger than a loonie. The wire is drawn or pulled through the vise and locks into a fixed position and it cannot be pulled back out but can be tightened if necessary. The locking mechanism can be described as being a 'one-way' locking device.
Vertical Axis Fig. - 3 - HIGH TENSILE STRENGTH strength smooth 12.5 gauge galvanized wire - Diagram - Fig. #3 - is recommended. This type of wire is dangerous to work with as can spring back and put out an eye. Wear eye protection and gloves when working with this type of wire. Do not kink the wire or it may break at that spot. Carefully roll the wire off the coil; do not lay it on the ground and lift if off. If the wire is not remove from the roll opposite to how it was put on the roll the wire will behave like a spring.
Vertical Axis Fig. - 4 - END ANCHOR POSTS are pounded in 4 ft at a 60° angle to the soil. This post is usually heavier than the in-line posts and longer so the wire remains at 7.5 ft with the post on an angle. The end posts are usually 14 ft in length with a 5 - 6 inch diameter. This is the key post so it must be set well. The wire when installed goes right over the top of the post and rests on a staple or two laying flat on the post top to prevent the wire from cutting deep into the post upon tightening.
Vertical Axis Fig. - 5 - IN-LINE SUPPORT POSTS are usually set 2 ft in undisturbed ground. Experience has shown that the distance between support posts should be no more than 30 - 50 feet. Length of row not to exceed 500 - 600 ft. This is for both strength of wire and ease of exit from the planting as needed, e.g. at harvest.
Vertical Axis Fig. - 6 - Install wire with large STAPLES on the wind-ward side of the in-line posts to resist pull out. Never on the top of the post as the staple will not hold well driven into the wood grain. Use a big galvanized staple and put on the side of the post 3 - 4 inches from the top.
Staples should be 1 ¾ inch galvanized staples (50% more pull resistance than the 1 ½ inch size). Slash-cut points better than diamond shaped points, as they help 'rotate' and set the staple. Double staple where wire rises or dips over hill/valleys. Never drive the staple home as this kinks, weakens and damages wire finish.
Vertical Axis Fig. - 7 - LEADER SUPPORT is the most costly part of the system as one is required at every tree. The support is usually set in the ground a few inches to stabilize the bottom. Install on the wind-ward side of the wire. Material used for the leader support must be strong, long lasting, easy to install and of low cost.
Vertical Axis Fig. - 8 - There are special FASTENER CLIPS available to hold leader supports to the wire so it does not slide along the wire. Some growers use snow fence ties or other soft galvanized wire.
N.B. Tree is usually tied on the lee-ward side
Support Systems for hail netting are not much different than what is described above except for using a longer post to get the ridge wire up to an elevation of 12 feet along the row. This normally requires inline posts to be 16 feet in length with 4 feet in the ground and 12 feet above ground. This height would support the ridge of the netting over the top of the row. The angle of the pitch going to the furrow between rows has to be sufficient to shed hail pellets down and off the netting between the edges of adjacent coverings.
As growers gain more experience, this list of suggestions will improve. Your comments on other items to add would be appreciated.
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