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Standard Trees versus Dwarf Trees
Trees on dwarf and semidwarf rootstocks are ideally suited for home fruit production. Although more expensive, the smaller trees are easier to prune, spray, and harvest; they also begin to produce fruit at an earlier age than full-sized trees. The two most dominating influences on tree size are the rootstock and the type of strain used (spur or nonspur). Other factors influencing ultimate tree size include general care, variety, soil type, earliness of fruiting, and time and severity of pruning.
Apple tree size as influenced by rootstocks is generally divided into three categories: standard (also called seedling), semidwarf, and dwarf. Standard trees are propagated on seedling rootstock and produce large trees that can grow to be 30 feet tall. Semidwarf trees are propagated on one of several clonal (vegetatively propagated) rootstocks that produce trees that will be about three-quarters the size of standard trees grown under similar circumstances.
True dwarf trees will be about 30 to 40 percent as large as standard trees and require support by either a trellis or a post. The two most common dwarf rootstocks are Malling 9 and Budagovsky 9 (commonly abbreviated as M.9 and Bud.9, respectively). Trees grown on Bud.9 are the smaller of the two. The most common semidwarf rootstocks used for apples are M.26, M.7 or M.7a, Malling Merton 106 (commonly abbreviated as MM.106, and MM.111. Trees on M.26 will produce the smallest trees while MM.106 will produce the earliest bearing trees. The MM.106 and MM.111 will produce the largest of the semidwarf trees.
Dwarf fruit trees often require fewer pesticides. Since the trees are smaller than standard-sized trees, air circulates better inside them and they dry off more quickly. Most diseases develop under wet conditions. Small trees that dry off quickly have a reduced potential for disease development and therefore require fewer pesticide applications to control disease. In addition, when pesticides are necessary, obtaining a uniform application is much easier on small trees. Uniform pesticide deposits are necessary for disease and insect control.
The interstem tree is another category of rootstock that might be available. It has a small stem section of M.9 grafted between an understock such as MM.111 or MM.106 and the variety. These trees are slightly larger than dwarf trees but smaller than the semidwarf. Because of the extra propagation needed, interstem trees are the most expensive. Current recommendations suggest planting these trees so that a portion of the M.9 piece is below the soil line.
Table 4.3 lists the space requirements and probable yields for fruit trees grown on different types of rootstocks. The spacings listed are minimum distances; wider spacings can be used.
b. Malling Merton trees require extremely well-drained soils to perform as advertised. Do not plant them where drainage is slow or the soil is heavy clay.