Growing Fruit Trees in Maine - Rootstocks and Dwarf Fruit Trees
Fruit trees are not grown from seed because seeds of fruit trees are not true-to-type for the variety. Seeds from a McIntosh tree will not grow into another McIntosh tree, but will be a unique variety instead. This is also true of seeds from other varieties and other types of fruit trees. True-to-type varieties are propagated by grafting buds or shoots onto rooted cuttings, called “rootstocks.” The grafted bud will grow into the above-ground portion of the tree, called the “scion.” The scion determines the variety of fruit that the tree will bear.
Trees are classed into groups according to their size, and these groups are dwarf, semidwarf and standard. Tree size of fully-grown trees is determined by both the scion variety and the rootstock. Varieties vary in their natural vigor with some being very vigorous and producing a large tree. Northern Spy is an example of a very vigorous variety and Honeycrisp an example of a low vigor variety. Trees size is also determined by its rootstock. Dwarf fruit trees are grafted onto dwarfing rootstocks. Standard rootstocks produce a full-sized tree. A particular variety can be grafted to a dwarf, semidwarf or standard rootstock giving the gardener a choice in tree size for most varieties. Dwarfing rootstocks are available for apple, cherry and pear. For peach, apricot and plum, fewer size controlling rootstocks are available so fully dwarf types are not an option. Most garden stores sell semidwarf trees, but specialized nurseries will offer a wider range of tree sizes or will offer a particular variety on a choice of several different rootstocks.
Rootstocks also influence how rapidly trees begin to bear fruit. In general, dwarf apple trees begin to bear two to three years after planting. Semidwarf trees begin to bear fruit four to five years after planting. Standard trees can take as much as seven to ten years to reach an age when they bear fruit.
A dwarf apple tree attains a height of eight to ten feet and can be planted at a distance of six to eight feet from other trees. Because of their smaller size, dwarf fruit trees are easier to prune and harvest. However, they require a permanent stake or trellis for support because of their brittle roots. The roots easily break causing the tree to lean when the tree is not staked. Dwarf fruit trees are a good choice where space is limited and trees are protected from deer. There are several dwarfing rootstocks available for apple, and some of these are described below.
Malling 27 (M.27) produces a very small tree of about five feet in height at maturity. These can be planted three feet apart from other trees. M.27 is appropriate when only a very small area is available. Trees on M.27 rootstock are available through specialty catalogs.
Malling 9 (M.9) and Budogovsky 9 (Bud.9) produce dwarf trees that reach about six to seven feet in height in Maine. Trees on this rootstock can be planted five to six feet apart. Budogovsky9 has greater winter hardiness than Malling 9. Either rootstock is a good choice for very vigorous varieties that are slow to bear such as Northern Spy.
Malling 26 (M.26), Geneva 11 (G.11) and Geneva 16 (G.16) are small semidwarfing rootstocks that produce a tree about ten feet in height and can be planted as close as eight feet apart for most varieties.
When pruned each year, semidwarf trees reach a height of 10 to 16 feet and should be planted 12 to 18 feet apart. Unpruned trees will require more space. There are several different semidwarfing rootstocks available, each having a different recommended spacing. Most garden stores specify whether the tree is dwarf, semi-dwarf or standard, but specialized nurseries specify the particular name of the rootstock.
M.7 is a semidwarfing rootstock that does not require staking, but lacks winter hardiness and is slow to bear fruit. Trees on this rootstock can be planted 12 to 14 feet apart. M.7 is most likely the semidwarfing rootstock of trees purchased from garden stores. Geneva 30 (G.30) is a better choice than M.7 for colder climates, but requires staking and is not widely available.
MM.106 and MM.111 are semidwarfing rootstocks that do not require staking, but require more space than dwarf trees. They can be planted at a spacing of 18 feet apart for most varieties. MM.106 lacks winter hardiness. They are useful for very low vigor or slow growing varieties such as Honeycrisp.
Standard or seedling apple rootstocks produce full-sized trees. Trees on seedling rootstocks should be planted at least 30 feet apart. They do not require staking and begin to bear fruit seven to ten years after planting.
Most pear rootstocks are semidwarfing. Pears are vigorous and should be spaced 20 feet apart. Quince is used as dwarfing rootstocks for pears, but lacks winter hardiness. Pyrodwarf is a new dwarfing rootstock that has not been evaluated in Maine, so its winter hardiness is unknown. Most Asian pear varieties are lower in vigor than European pears and can be planted 12 feet apart.
The cherry rootstocks Mazzard and Mahaleb are very vigorous. With sweet cherry, they should be spaced 25 feet apart. Colt is semidwarfing and can be spaced 20 feet. Gisela 5, a dwarfing rootstock, can be spaced 10 feet. Tart cherries are less vigorous and can be spaced 15 to 20 feet apart depending on the vigor of the variety.
Most peaches and other stone fruit are grafted onto standard rootstocks. Several new rootstocks are available for plum and peach, but have not yet been evaluated in Maine. Peach and plum trees should be planted 15 to 20 feet apart.