Richard C. Funt
With the advent of size-controlling rootstocks for fruit trees and high density plantings, growers have developed a renewed interest in trellis supports for fruit trees. This is especially true with apple cultivars on the most dwarfing rootstock, M9. Trees trained and secured to wire trellises have been estab lished in home plantings. This method of growing apples can accommodate from four to six dwarf trees between two posts, depending upon planting distances. Most other rootstocks result in growth that is too vigorous for economical trellis training or are not adaptable to Ohio soils.
The trellis may be constructed for three to six or more wires, depending on vertical spacings of the wires and the ultimate height desired. In most instances, the wires are spaced 18 to 24 inches apart vertically with the bottom wire 18 to 24 inches from the ground. The height of the top wire is determined somewhat by the harvesting method to be used. If all picking is to be done from the ground, the top wire would be six feet from the ground. If a picking platform or short ladders are anticipated, it could be 8 to 10 feet from the ground.
The cost of available posts of the desired length would be a determining factor. Posts to carry the wires may be set before or after planting the trees with the line posts spaced 35 to 45 feet in the row and located halfway between trees. End posts should be anchored. The wires, usually No. 9 galvanized or three to four mm monofilament (not recommended for spur type Delicious), should be in place and secured firmly to the posts by the middle of the first growing season.
Training begins at planting. If no branches are present near the bottom wire, head the tree at the height of the bottom wire or four inches below, in the case of Delicious. This will induce branching just below the wire. The uppermost new shoot usually grows in an upright position and assumes the position of a central leader. At least two other shoots will arise below this one. The two most suitable branches are tied loosely (plastic ties) to the bottom wire as soon as they are long enough, one in each direction. Any other shoots are cut back to short stubs. In tying a shoot to a wire, do not bend it downward to a level that the tip is at a lower level than the point of attachment on the trunk. To do so greatly retards extension shoot growth. The shoot will be in the best position when the tip is a few inches higher than its base. Also, this position is less likely to induce vigorous risers on the scaffold (Figure 1). Growth of the uppermost shoot should extend well beyond the second wire by the end of the first growing season.
During dormant pruning the next spring, head back this central stem at a point just below the second wire. Branching will occur just below the cut. Tie two of the lateral shoots, as they develop, to the second wire - one in each direction. Train the uppermost shoot to the central leader position. For production efficiency, it is important to cover the trellis with fruiting wood as quickly as possible. If possible, it is best to bend by tying shoots that compete with primary laterals rather than delay fruiting by pruning. The branches trained to the lower wire need little pruning the second year, other than to maintain terminal growth and to prevent vigorous upright shoot growth. Strong upright growth is headed back severely so as to contain it well below the second wire.
Pruning during the succeeding years of training will be similar to that described for the second year until the basic framework is complete.
When the central leader reaches the top wire, one of two procedures may be followed. The leader may be bent in one direction and tied to the top wire. Then, when a lateral shoot develops below the bend and becomes large enough, it may be secured to the wire in the opposite direction. The other procedure is to head the leader just below the top wire. When new lateral shoots develop, tie the two uppermost to the top wire, as soon as they have sufficient length, extending each in opposite directions. The latter method gives a little more assurance of adequate branches for developing into scaffold branches.
As the arms or scaffold branches touch those of the adjoining tree, an overlap (10 to 20 percent) may be desirable to insure all portions of the trellis are covered with fruiting wood. Each year, after the fruiting wood covers the trellis, pruning should be limited to thinning out to insure good sun light penetration. Extra scaffold shoots left in during the early years should be removed gradually over a three to four year period to permit no more than one primary scaffold per side per wire. Prune side branches lightly with thinning cuts to maintain the desired three to four feet width of tree row.
Mature plantings in the trellised hedge-row system require only a moderate amount of annual dormant pruning. It is often helpful to go over the planting in August each year and remove excessive or unwanted shoot growth.
For additional information about growing fruit, obtain a copy of Extension Bulletin. 528, 'Training and Pruning Fruit Trees', Bulletin 591, 'Growing and Using Fruit at Home' and, Bulletin 780, 'Controlling Diseases and Insects in Home Fruit Plantings'
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Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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