Did you know that when you buy an apple tree you are really getting two trees? You are getting two genetically different apple trees grafted together. The part that produces the apple is called the “scion.” Haralson and Honeycrisp are examples of scion cultivar names. It has been grafted onto a “rootstock.” You should pay as much attention to which rootstock you buy as to the scion.
The rootstock you choose will contribute to the mature tree size, anchorage, hardiness, adaptability to different soil types, the number of years before the fruit is produced and the ease of care for the tree.
According to Doug S. Foulk, an Extension educator in Ramsay County, horticultural professionals recognize at least three rootstock categories; standard, semi-dwarf and dwarf. Standard trees reach full size, 16 feet or more. That is depending on the vigor of the scion, cultivar and the environment. The older Honeycrisp has only lived about 30 years before failing.
Semi-dwarfing rootstock produces a tree that will be between 10-15 feet tall, perfect for most landscapes. Of course this depends on the vigor of the scion cultivar and the environment the tree is grown in. No tree, no matter it’s size, will grow to its true potential if not watered regularly, pruned properly and in good soil. These semi-dwarfing trees are often sold as dwarfing rootstocks. A true dwarfing rootstock generally restricts the tree height to 10 feet or less. A true dwarf tree takes only 2-3 years to fruit. You don’t need a ladder to prune or pick fruit on this little girl. One bad thing is that they are not as long lived as a standard tree.
Standard root stocks are generally more winter hardy, more tolerant to wetter or drier soils and are better anchored (more and longer roots) than the other two. It will take the larger tree longer to bear fruit, 5-7 years, but you will get a larger crop.
When you go to the nursery, will you know which rootstock you are getting? Probably not although nurseries, both mail order and local are beginning to list the specific rootstock as individual rootstocks have their own set of advantages and disadvantages. You should know which rootstock is used on the tree you are buying. It will give you a better idea of how to handle your tree for better success.
MM111 is a semi-dwarfing rootstock sometimes called semi standard. It is extremely hardy. It produces a tree 80% the height of a standard tree, is well anchored and can withstand drier soils.
M. 7a also called EMLA 7 is the least hardy of the semi-dwarfing rootstock. It suckers profusely but doesn’t require staking. M26 and M9 produce trees that need staking. All are susceptible to fire blight.
A Russian import, Budagovsky 9, shortened to Bud 9 rootstock grows trees 6-8 feet tall. They do need staking for life but produce fruit early and have few suckers. Hardiness has been excellent. Other hardy rootstocks are from the “Polish series.” P2, P22. Mr. Foulk has no more to say about them.
When staking one of these petite trees, use a stake on both sides of the tree. The tie should be loose so the tree can sway in the wind. This makes the trunk stronger. Never let a new apple tree of any size become overburdened with apples. Too many will break the branches and lead to fewer or no apples the next year. Thin apples to one per bunch and bag for bug-free apples.
Bev Johnson is a Master Gardener with the University of Minnesota Extension. Her column appears in the Weekend Edition.