Espalier is the term used to describe the process of training trees, shrubs, and woody vines against a flat surface, such as a wall. You can also train them to a freestanding fence or trellis. To espalier, prune to create a main vertical stem, then train the side branches to achieve the desired shape. Depending on the plant, this can take a year or two to establish and requires regular care. Thereafter, an espalier requires only light pruning to hold its shape.