The formalized shape of a flowering plum tree against a wall or wooden trellis will be especially pretty in spring with the appearance of blossoms. Selecting evenly spaced branches on the plum tree in a single, flat plane provides the main structure for the espalier. Trimming back side twigs twice annually ensures the plum tree remains neat in appearance while the branch tips elongate to the desired length.
Creating the Espalier
Examine the plum tree, looking at its branching structure. Ideally find a spray of branches off of the trunk that are nearly in one plane that is parallel to the wall or trellis the espalier is to be attached.
Determine, based on the plant's branch structure, if the espalier shape is best as a fan or ladder. A fan-shaped espalier has branches that emanate from the trunk and spread out in increments, like the spacing of your fingers on an open hand. The ladder has branches equally positioned that grow horizontally like the runs of a ladder.
Prune away all small twigs and branches from the trunk that are not the main structural branches to form your espalier. Make the cut 1/4-inch above the trunk attachment with a crisp, one-motion clasp of the pruner blades. When done, only the branches you selected to be the main structure of the espalier should remain.
Remove side shoots and twigs from your remaining espalier branches with the pruners. Create main espalier "arms" with the branches so that they are long and lack side twigs and branches. Make the pruning cut 1/4-inch above their attachment to the main espalier arms. Do not prune the tips of the main branch arms.
Gently secure the main espalier branch arms to the wall or trellis in the shape you desire. Tie the branches with old nylon stockings or natural rope or string. Allow the branch to wiggle slightly in the tie so wind does stress the joint and the branch has room to grow in girth. Do not apply excessive pressure on branches and joints so the branches might snap or break.
Allow the plum tree to stabilize and grow in the shape created for the growing season. Re-do ties as needed and add ties to branches to secure them to the training trellis at their ends as they grow or flop.
Maintaining the Espalier
Prune back twigs and new growth on the main espalier branches in late winter to one or two dormant buds. When the pruning is done, there should be many short twig stumps or spurs along the long main branches of the espalier form.
Tip prune the length of the main espalier branches in summer once the final desired length is reached by the plant. To maintain a main branch at a length of 5 feet, for example, allow the branch to first grow to a length of 6 feet and then tip prune it back to the desired length of 5 feet.
Remove the current year's leafy and twig growth in midsummer by pruning them back to preserve the overall main espalier form. Trim side shoots on the main branch arms back to a length of 2 to 4 inches so that a few leaves or fruits remain.
Follow-up with Step 1 again in late winter, maintaining the structure and shape of the espaliered plum tree. Establishing the most handsome, well-shaped espalier will take 4 to 5 years of repeating Steps 1 through 4.