"Espalier" is the cultivation art of growing trees against wires or a trellis, either as a free-standing fence or up against a wall. Espalier trees are attractive and produce abundant fruit in a very limited amount of ground space. Apple trees make effective espalier specimens. The best rootstocks for espalier apple trees are productive, dwarfing types that maintain a smaller tree suitable for training.
The M27 dwarfing rootstock is desirable for espalier apple trees, according to the Chicago Botanic Garden, as using a larger, full-size rootstock will result in a tree with a thicker trunk and limbs that are not as amenable to the bending and training necessary to achieve the desired espalier effects. The M27 is a very dwarf rootstock, not suitable to standard orchard growing, reports All About Apples, but it does produce early-bearing, prolific apple trees. Its small size requires firm support from tying and staking, which is provided by the espalier process. Apple trees grown on M27 rootstock will generally reach approximately 6 feet tall, with limbs 3 feet to 4 feet long. This is an ideal size for espalier, according to the Chicago Botanic Garden.
The M9 rootstock is ideal for growing supported apple trees on a trellis espalier system, according to the Ohio State University Extension. Training apple trees along wire fences, akin to the method of cultivating grapes, results in more fruit production in a smaller space. The M9 is the most important dwarf apple rootstock in the world, reports Cornell University. This rootstock produces trees about 10 feet high, with large fruit size and early harvests. The M9 is cold-hardy and tolerates wet soils, but it is not drought-resistant, and its brittle roots require sturdy staking. Espalier growing provides the support and protection from wind and storm damage necessary to be successful with this rootstock.
The Bud 9 is an appropriate dwarfing rootstock for espalier apples, according to the Ohio State University Midwest Home Fruit Production Guide. The Bud 9 stock produces a full dwarf tree, slightly larger than the trees produced on an M9 rootstock. The Bud 9 is also very productive and extremely winter-hardy, as well as resistant to collar rot, powdery mildew and apple scab, reports All About Apples. The Bud 9 is not drought-resistant, however, and will require regular watering if regular rains do not provide enough water. Bud 9 apple trees produce a prolific early harvest, but, as with other dwarfing stocks, the Bud 9 tree will require staking and support, as its roots are brittle.