Dwarfing Apple Rootstocks: Pros and Cons

Dwarfing Apple Rootstocks: Pros and Cons

To Be or Not to Be Little. That Is the Dwarf Fruit Tree Question.

By Guy K. Ames, NCAT Horticulture Specialist

At right: The author beneath a full-size Koyama pear tree. Photo courtesy Ozark Natural Foods.

Whether ‘tis nobler to suffer the posts and cables of outrageous trellis systems… Okay, I’ll stop. Most professional orchardists and amateur gardeners seem to greatly prefer smaller dwarf trees. However, the rootstocks that underlie the dwarfing itself are not without problems—the need for outrageous trellis systems among them. Let’s take a short look at the pros and cons of these short trees.

Before going further it needs to be said that there are some good dwarfing cherry rootstocks and some promising pear dwarfing rootstocks. However, in general, rootstock research and positive results for other fruits lag far behind the apple rootstock situation. Accordingly, this short essay focuses on apple rootstocks.

A Brief History of Dwarfing Apple Rootstocks

The British began the era of dwarfing rootstocks with the first release of named rootstock varieties for apples in 1912. These first, and the many following, including dwarfing rootstocks for cherries and peaches, came out of the research stations at Malling and Merton, England. These rootstocks now dominate the world’s apple orchards and still bear the designations “M” (for Malling) and “MM” (for Malling-Merton) for their origins. Professionals and the more ardent amateurs will recognize these names: M.9 (most widely planted rootstock in the world), MM.111, M.26, MM.106, M.7, and so on.  These are all clones, of course, with predictable characteristics such as percent dwarfing (compared to a “standard” tree grafted to rootstocks grown from apple seeds), ability to induce precocity (cause the tree to bear at an early age), free-standing or needing support, resistance or susceptibility to certain diseases or insects, and so forth.

By the way, though the Brits started it, the Russians, French and others have made their own contributions. Possibly the most comprehensive and valuable American research into dwarfing apple rootstocks has come out of Cornell University. Cornell’s research appears now to be making significant contributions to commercial apple production, at least in the U.S.

Revolutionary Rootstocks

Dwarfing Apple Rootstocks on Trellis
Dwarf apple trees supported by a trellis system at the University of Arkansas. Photo: Luke Freeman, NCAT.

The small stature of the “fully dwarfing” apple rootstocks, like M.9 and M.26, combined with their precocity have revolutionized apple orcharding world-wide. The modern orchard might look more like a strange grape vineyard at first glance. These roots, frankly, are weak and need the help of a trellis to hold up the weight of the upper tree, especially when these trees begin fruiting at such a tender, young age. Gardeners are more likely to stake such trees individually like a tomato or a prize rose.

At any rate, these modern full dwarf fruit trees are a far cry from the image a lot of us might have in our heads of a 25-30-feet-tall apple tree with a swing attached and ladders propped against. An unstaked or untrellised, modern dwarf apple tree with a full crop is very likely, especially with a little wind, to just fall over! It could never support a swing! No child will ever scramble up such a tree because there is essentially no “up” to it.

Nevertheless, these small fruit trees have a lot to offer growers. The stature means that spraying and harvest are greatly simplified and can reduce labor and machinery costs. And bearing fruit quickly after planting is not only satisfying to the home gardener but, importantly, allows the professional orchardist a quicker return on their investment, which is considerable. An orchard planted on standard seedling rootstocks might take four to eight years to come into bearing while an orchard on dwarf stocks might only require two to three years.

Disadvantages of Dwarfing Apple Rootstocks

So there have to be some downsides to these little trees, besides not having the satisfaction of climbing or swinging from an apple branch. Yes, there are problems. First, and already mentioned, is the necessity of supporting these trees.  Second, their small, restricted root systems require more careful attention to both watering and fertilizing. They simply are unable to better fend for themselves.

Third, all the rootstocks with the single “M” designation turned out to be susceptible to the wooly apple aphid, a root aphid that can do serious damage when conditions are favorable. The Merton station’s main research goal was breeding for wooly apple aphid resistance, and they succeeded. Thus, all “MM” (Malling-Merton) designated rootstocks are resistant to this pest.

Fourth, most of the full dwarf rootstocks are susceptible to fire blight. Some of them—as well as of some of the semi-dwarfing rootstocks like MM.111 and MM.106, which are roughly half-way between standard and full dwarf height—are susceptible to other disease problems like root rots and parasitic nematodes.

Lastly, and more-or-less because of the combined effects of these other problems, the dwarf tree is not going to live nearly as long as a standard tree. A standard tree will be better able to fend for itself during tough times. Standard trees are just better able to tolerate the feeding and privations of diseases and insect pests. Most full dwarfs are lucky to make it to age 10 to 15. A standard apple tree, depending on geography/climate, could live 30 to 200 years!

This photo illustrates one of the disadvantages of a full-sized tree: much of the harvest must be picked from a ladder! Photo: Robyn Metzger, NCAT.

Choosing Your Rootstock

So, all in all, there are serious trade-offs involved in choosing a dwarfing rootstock or a standard rootstock for your apple trees. Commercial apple orchardists have developed comprehensive systems for making the most of dwarf trees and they are paying off for them. Home growers, however, might want to consider the pros and cons. An older gardener, wary of ladders and thinking his time on Earth is limited, might go with the dwarf tree. On the other hand, the same gardener might have a comforting image of his grandchildren climbing an apple tree to pick their own fruit. Young orchardists, especially permaculturists, might want to reconsider some of the benefits a larger, longer-lived tree can impart to their farms. One size doesn’t fit all.

Additional Information

For more on apple production, see ATTRA Sustainable Agriculture’s publication Apples: Organic Production Guide.  You can also contact Guy or our agriculture specialists directly with questions! Email askanag@ncat.org or call 800-346-9140.

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