There is a lot of confusion in the retail nursery market about “dwarf” apple trees. What makes an apple tree dwarf? Why would somebody want a dwarf apple? How dwarf is dwarf?
Let’s start with the basics. Apple varieties must be cross-pollinated to set fruit. This means that apple flowers must have pollen from a different apple/crabapple variety in order to set fruit. This is why you must plant 2 different apple varieties (unless you have a crabapple nearby). The seeds produced in the apple will be a hybrid of the 2 parents but the fruit will always be the same as the parent tree. Because of this, one cannot plant seeds from a McIntosh apple & have it bear McIntosh fruit!
To propagate an apple variety, a branch from the desired variety is grafted or budded onto a rootstock. This is a form of asexual propagation. Years ago, apple seeds were grown out to be used as rootstocks. Seedling rootstocks were variable in rooting characteristics, hardiness, ect. They are still used today to some extent. As the hunt for better rootstocks went on, many selections were made that were a vast improvement over seedlings. These rootstocks were named & are used for better uniformity, greater cold hardiness, height control, ect.
Standard apple trees are no longer used much except in extreme cold areas of the U.S. They are called “standard” as the desired apple variety is budded/grafted onto rootstock selections that result in a full sized tree ( averaging 18’-30’ tall). Standard apple trees also are slow to start bearing fruit until about 5-8 years of age. Most yards today are too small for such large trees & nobody wants to wait 8 years to get some fruit!
There are many “dwarfing” rootstocks in the trade that will reduce the size of the apple tree & also make it bear fruit in about 3 years from planting. Hooray! Great news for the backyard orchardist! Please note that a dwarfing rootstock only reduces tree size, not the size of the fruit.
Some “dwarf rootstocks” are more dwarfing than others. What dwarf rootstock is used also depends on the general vigor of the apple variety propagated. Some varieties that are extremely vigorous are grafted onto more dwarfing rootstocks & those that are less vigorous are put on rootstocks that are less dwarfing to compensate for this. The final outcome is trees that offer great height control.
The most common dwarfing rootstocks for apples are M26 & M7A. Apples on M26 are considered “dwarf” & those on M7A are considered “semi-dwarf” but one cannot assume all apples called “dwarf” are on M26 as there are other “dwarf” rootstocks besides M26. Likewise for M7A. Thus the importance of listing what rootstock the apple is on! I have seen apples trees on M7A sold as “dwarf” at many garden centers! This can be a problem if they also have varieties on M26 listed as “dwarf”. Should a homeowner buy 2 apples & each is on a different rootstock how will they know how much room the trees will require if not properly labeled?
Apple trees on M26 rootstock generally will grow 10’-12’ tall & should be spaced 12’ apart. M26 is a delightful rootstock for the homeowner & is quite cold hardy. Sometimes in youth, trees on M26 may tip slightly. If this occurs, the tree may require staking. This does not always happen & the benefits of the reduced height & the ability to bear fruit in 2-3 years from planting far outweigh this possible disadvantage.
Apples on M7A usually will grow 14’-16’ tall & should be spaced 16’-18’ apart. M7A is a very important rootstock for commercial orchards. The only bad news is that M7A sometimes produces root suckers prolifically which can be controlled by pruning should that occur. Apples on this rootstock usually start producing fruit 3 years from planting.
Both rootstocks are highly recommended for the backyard gardener. Just be sure that next time you buy a “dwarf” apple tree that the rootstock is properly labeled. If not, ask the sales help. This way you will know what to expect when the tree is full grown & also how far apart to space out the trees. Having this knowledge at planting time will prevent a lot of problems in the future.