Establishing the High Density Supported Apple Orchard

Part 3: Choosing a Tree Training System

Table of Contents 

1. Basics of Supported Tree Training Systems:
   1. Slender Spindle (SS)
   2. Vertical Axe (VA)
   3. Trellis
2. Comparing the Systems

 Basics of Supported Tree Training Systems

M.9 will require tree support for the life of the planting. In fact, all trees on any rootstock in a high density system need tree support. This can be accomplished with several different structures.

There are 3 supported training systems which have been most commonly used by apple growers in Ontario:

1. Slender spindle (SS)
2. Vertical axis (VA)
3. Trellis   

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 Slender Spindle System

This is the system preferred by growers who wish to work exclusively from the ground and are not confident in building wire support systems. The slender spindle (SS) consists of an individual support post at every tree.

Figure 2 Slender Spindle Support System (taken from Support Systems for High-Density Orchards, K. B. van Dalfsen, B.C. Ministry of Agriculture and Fisheries, 1989)

The post should be 2.4 - 3 m in length and of pressure-treated wood, concrete or metal to ensure it lasts the life of the orchard (perhaps 12 - 18 years). A diameter of 4 - 6 cm is preferred, since risk of frost heaving increases with larger diameters. The depth of the post in the ground should be 60 - 90 cm for stability leaving 1.5 to 2.5 m above ground. A common mistake is to have insufficient post height above ground. Some growers have tried to correct this condition by adding extensions at the top for more height.

The tree is trained to a slender bell, or pear shape with the bottom whirl of branches acting as a permanent fruiting table. The leader and top of the tree is kept quite weak to contain height. Renewal pruning of mature trees consists mainly of removing 2 - 3 of the largest diameter branches on an annual basis during the dormant season.

Tree height does not exceed 2 - 2.5 m.

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Vertical Axis System

The vertical axis (VA) system has been touted by some growers as the next logical step from free standing central leader trees to high density supported systems. The main reason cited is the great similarities between the systems and the low emphasis on limb manipulation by tying. There are ladders used in picking, but with a flat tree wall at ladder height it is quite fast and simple to manage ladders.

Even though the VA system is one of the taller systems used in high density supported systems, there is still a critical need for lower limb development. These lower limbs will form a fruiting table yielding perhaps 60% of the crop and must be established before the trees should be allowed to grow taller. Proper development of the bottoms of the tree will allow 75% or more of the fruit to be picked from the ground. Cultivars that have a high requirement for light (e.g. McIntosh) are well suited to this system. Other cultivars like Gala, Goldrush, Golden Delicious and Empire have a growth habit highly suited to this system.

Figure 3 Vertical Axis Support System VA systems allow trees to grow taller than SS systems. The system basically consists of one or more high tensile steel wire(s) drawn tight and supported 2 - 3 m above the ground by a series of in-line posts spaced 9 to 15 m apart. The closer the spacing for the inline posts, the higher the degree of stability of the support system under strong wind or high cropload conditions.

Individual trees in the row are supported by vertical leader supports that reach up to the top support wire. The tree consists of a conical, or "Christmas tree" shape and grown up to 3.5 - 4.0 m tall. The leader is not pruned until the tree reaches its full height. Shoots arising on the side of the axis or trunk close to and competing with the leader are removed as they arise or during the dormant pruning season. Side branches on the leader are renewed on a periodic basis.

The VA support system is somewhat more complex than the SS to install. It does require a high level of skill to build the support system and be sure it is adequate to hold the trees and crop load. A post failure in this system can result in the loss of several trees. The standard anchoring system now in use is the "auger anchor" which is screwed into place. Posts are generally pounded or watered (water gun) into the ground. More information on building the VA support system is available from the Apple Team. 

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Trellis Systems

The various trellis systems require a similar set up as that described above for VA. The number of wires used can range from 3 - 5 in simple vertical trellises and up to 10 - 12 for a tatura or Y-trellis. Unlike the VA there is no support along side each individual tree. Instead, branches are trained horizontally along the wires.

Figure 4 Trellis Support System (taken from Support Systems for High-Density Orchards, by K. B. van Dalfsen, B.C. Ministry of Agriculture and Fisheries, 1989)

If you are planting a trellis system it would be wise to follow the specific guidelines for whichever system you select. The key problems of trellis systems are varieties with excessive vigorous or strong rootstocks that result in excessive pruning to contain the tree. Also, trellis systems support the total weight of the crop load and, as a result, must be exceptionally sturdy with posts for wire support located every few trees in the row (much closer, than the VA system).

Super Spindle - There is some interest in this system in Ontario. The super spindle is characterized by very close in row spacing at less than 1 meter. From planting onwards, all structural wood coming from the main axis of the tree is pruned off. Trees are shaped to a very narrow columnar look. The hugh advantage to this system is in labour savings. Anyone sent into the block to prune follows the 50% rule.

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Comparing the Systems

In terms of installation costs the VA is slightly less expensive than the SS which is slightly less expensive than a trellis system. This varies depending on the availability of supplies to build the various systems. A one-year whip can be used in trellis and VA systems. Two year feathered trees are preferred for VA and essential for SS plantings. If a grower is starting the planting with a "sleeping eye", then they can expect to pay special attention to the training and development of the shoot that arises from the dormant bud or "sleeping eye". This usually requires the use of a supporting bamboo stake to ensure a straight and vigorous new whip.

As stated earlier, the advantage of all three systems, when planted to appropriate cultivars and dwarfing rootstocks, is early production (precocity). These are labour efficient since all can be worked from the ground.

Of the three systems, the trellis system probably requires the most pruning (winter and summer) to maintain horizontal scaffolds trained to the wire support. The SS would be next in labour requirements to train the tree, the VA has the least labour costs to train and manage. Care must be taken when using pneumatic or back-pack operated pruners and loppers on wire systems, to avoid damaging the wire(s). Pruning and training costs also vary greatly depending on cultivar growth habit.

Harvesting may also be challenging in wire systems because of the solid barrier nature of the tree row.

The economics of production between the SS and the VA do not differ significantly. It is a personal preference that steers growers to one system or the other. A technical document titled, Cost of Production - High Density Supported Apple Orchard is available from the Apple Team.

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