The cordon apple or pear tree has a single stem or leader from which grow the short laterals and sub-laterals (light pruning keeps them that way). The tree is seldom more than 18 inches wide. The stem of the tree is tied to the slat as it grows. These training aids for the young tree can be removed once the tree has reached its full height. 1. Begin by anchoring posts into the ground (2 feet deep) no more than 10 feet apart. Provide further support by using a guy wire at each end. String three wire strands between the posts, the first at 18 inches above the ground, the second two feet above it, and the third another two feet up.
Attach wooden slats or stakes to the wires at a 45-degree angle where each tree will go.
Dig the planting holes and buy young one-year-old whips of a heavily spurring dwarf variety from the nursery.
Plant the trees and carefully bend over the whip or stem and tie it to the angled slat. Use surveyor's tape for tying, since it's soft enough to yield to the broadening stem as it grows.
2. Regular summer pruning of the trees is vital to cordon fruiting. In mid-June cut back all lateral branches to four buds or 4 to 6 inches. Sub-laterals (branches of the branches) will develop at this stage. In mid-July cut back laterals to two sets of leaves and sub-laterals to about 2 inches. Repeat the procedure for your final summer pruning, in mid-August, and for all prunings in subsequent years.
3. On each cluster of short branches, stubby fruiting spurs will begin to develop, on which the following year's blossoms and fruit will appear.
Don't cut back the central leader until it has grown a few inches above the top strand of wire, when it will have reached the final height needed for this system.
By reducing vegetative growth, summer pruning forces the tree to divert much of its energy into fruiting spurs. As a result these trees develop fruiting spurs much earlier than free-growing trees.
Eventually the spurs become so thick that they have to be thinned out.
Horticulturist Steven Frowine recommends a permanent mulch around these trees. The continually decaying mulch will eventually provide all the food your trees need. In the first year or two, however, you may want to fertilize lightly.
Too much rapid-release fertilizer, however, will stimulate far more growth than you want for the system.
(For more detailed pruning information on cordons and espaliers, Frowine recommends the book ``Pruning'' by Christopher Brickell, Simon and Schuster, $8.95.)