To make the crisscross espalier known as a Belgian fence start with 8-foot-tall, 4-inch square posts of rot-resistant wood, such as cedar, locust, or pressure-treated lumber.
1. Sink posts at least 2 feet deep, preferably in concrete, and about 8 feet apart. Then, measuring up one side of a post from ground level, mark off uniform intervals (anywhere from 18 inches to 2 feet). Transfer the marks to the other posts using a water level.
2. Drill a hole through intermediate posts at each mark. On a post or frame wall at either end of the fence, drill just deep enough to make pilot holes for screw eyes.
3. Secure wire to screw eyes at one end of fence.
4. Thread wire through holes in intermediate posts, and stretch it taut, using a turnbuckle.
5. Space trees at a distance equal to the vertical interval between parallel wires; attach trunks loosely to lowest wire with twine. Arborist Bill Miller recommends planting at least ten to fifteen whips (unbranched shoots) or saplings in a row in order to get the desired lattice effect.
6. Locate two opposing side buds on each stem near level of lowest wire. Cut stems just above them. Remove all other branches.
7. The result is a uniform row of stems. A year after the planting, branches emerging from buds will give each tree a Y shape. From then on, pruning consists of shortening additional vertical shoots to within 2 to 3 inches of branches. Do not prune out spurs, knobby side shoots where fruit will form. (Instead of starting from scratch, you can buy trees already trained into Y shapes. You’ll still need to construct a frame.)
8. At the point where each diagonal branch intersects with another, tie both to a horizontal wire. As the trees mature, Miller says 80 percent of pruning should focus on their tops: “Vigorous top pruning will help get sun to lower branches, giving you a leafier, more substantial fence.”