Regarding pruning a of a plant for espalier, if you start with an unpruned plant, be sure to plant it far enough away from the base of the wall, and prune sparingly until the plant becomes established. Then, regular pruning and training as desired can be accomplished.
The secret of satisfactory results with espalier is to begin with a younger tree or shrub that has several well balanced limbs off the main trunk.
There are numerous patterns from which to select. These range from the formal checker-board patterns to the simple informal natural growth spread. Almost any design can be worked out with proper pruning. remember though, the simpler the design, the easier the maintenance.
To maintain an espalier, remove all stray branches that appear vertical; growing out too far from the flat wall surface and beyond the boundaries of the desired pattern and shape. Pruning and the occasional tying of new shoots to the surface of the wall are the main maintenance jobs.
Most of the major pruning should be done while the plant is dormant, or if it is a flowering plant, be sure to prune in the appropriate season. Most flowering shrubs and trees should be pruned just after they bloom except for ones like crape myrtles which should be pruned in February or March. Remember that pruning stimulates more growth. The limbs are most flexible during the summer. One can bend and train them to supports as the season progresses.
Once established, the espalier tree or shrub requires only a small amount of maintenance each season, yet it contributes year-round distinction to the garden. A plant which has been espaliered correctly is a real work of art. Patience, skill, and creativeness is necessary for a successful project.
Below are a few images of plants that visually show how plants can be used as espalier. Some of the plants in the images have been planted close against the wall and allowed to grow naturally, while others have been formally trained to grow in various shapes and patterns.
Granny Smith Apple Tree
Little Gem Magnolia