The graceful sweep of espaliered berry canes growing across a sunny wall is among the loveliest garden views. Given the structural support of a wall, trellis or fence, the blackberries are trained to grow out wide and flat on stretched wires. The fruit yield can be boosted by the good air circulation and sunlight exposure. Espalier blackberries by tying the fruiting canes to one side and the new growing canes to the other. With more than one plant, alternate the sides so that like canes meet each other.
Plant the blackberry canes directly beneath a wall or fence in sunny spot. Part shade is also acceptable, but make sure the site is protected from the wind. Feed with compost each spring and mulch the blackberry espalier with 3 to 4 inches of mulch each autumn.
Create an espalier grid by pounding nails into the wall or fence. The nail rows should extend as long and as high as you wish the blackberries to grow at their maximum. Use galvanised nails on wood so they will not rust and use masonry nails on stone or brick.
String a thin galvanised-steel wire from nail to nail, creating grid squares. Secure the wire onto each nail by twisting it once around the head. When completed, each nail should look connected by wire to the nail next to it on each side, above and below.
Tie the growing canes to the wire grid with string or plastic-covered wire. Tie them to create the shape you wish to see in espalier. Tuck very thin stems behind wire to hold them until they are large enough to tie.
Separate the blackberry canes after the first fruiting. Prune the fruit-bearing canes deeply and tie all toward one side of the espalier. Tie the non-fruit-bearing canes to the opposite side and trim lightly in autumn or the following early spring. The canes that bore no fruit will do so the following year and more new shoots will grow from the old canes. These will bear fruit again after one season passes.
Manage the old and new canes on the blackberry espalier by keeping track of which canes have fruited in the current year and which are new. With the knowledge of which canes are due to fruit, you will always know which canes to prune deeply and where to train new growth from old canes. Continue to manage the espalier, and by pruning and tying you can achieve the shape you desire.