What is a rootstock?
The apple tree rootstock controls the tree’s size, precocity, cold hardiness, and partly its disease resistance (such as fireblight). In order to grow a reliable and high quality fruit tree, growers graft the scion, which is above the ground and responsible for the fruit’s characteristics and disease resistance, onto the rootstock, which is underground.
In this article we will cover:
- Apple Rootstock Development History
- Common Apple Tree Rootstocks
- Selecting Apple Tree Rootstocks
Apple Rootstock Development History
Although fruit tree growers practiced grafting for centuries. Most of the rootstock growers now use have only been developed in the 20th century. Dr. R. Hatton at England’s East Malling Research station helped start this work by gathering 24 different rootstocks and naming them. As a result of his work, we now have M selections such as M9, M7, M2, M8 and M13 (note that the number in the name of the rootstock doesn’t correlate to tree size). However many of these rootstocks didn’t have strong disease resistance. For example, one of these diseases is woolly apple aphid which causes swollen enlargements to form on the above-ground portions or roots of the tree where aphid colonies feed on twigs or roots.
So in order to create woolly apple aphid resistant rootstocks, in 1917, the John Innes Institute of Merton England joined with East Malling Research Station and developed the popular Malling-Merton rootstocks, MM106 and MM111.
Then in the 1960’s, in order to create even more disease resistant rootstock, East Malling and Long Ashton research stations joined together in England and created the EMLA rootstocks which are virus free clones of the MM series. Many growers now use the EMLA series.
There have been other great rootstock that have emerged such as the Budagovsky series (known as Bud or B). This series originated from the Michurinsk College of Agriculture in the former Soviet Union.
Yet, the latest and most distinguished rootstocks have been the Geneva series which Cornell University developed (also known as G). In fact, these rootstocks are powerful since researchers developed them for their tolerance to fire blight, Phytophthora root rot, high yield efficiency and good tree survival.
Common Apple Tree Rootstocks
Below, we describe the most popular and successful apple tree rootstocks and their characteristics, such as the height at maturity.
- However, while a rootstock does affect the size of the tree at maturity, the variety of apple, the soil type, the amount of sun and the way the tree is pruned will also have a significant impact on the ultimate height.
- For example, an apple tree on an M9 rootstock can grow to the same height as one grown on an MM106 rootstock with the appropriate care. However, the M9 tree will have fewer and thinner branches.
- Therefore, when you see below the height of the tree at maturity, it is an approximate maximum.
Dwarf Apple Tree Rootstock 6-10 ft
Note: When planting trees on dwarf rootstocks, you can plant them generally about 5-7 feet apart.
Researchers bred Bud. 9 (also known as Budagovsky 9 or B.9) in the Soviet Union by crossing M.8 x Red Standard (Krasnij Standart). This dwarf rootstock is resistant to collar rot and very cold hardy. Additionally, it’s about 15-25% smaller than M.9. However this depends on the cultivar and site you grow the trees on.
M9, like other dwarf rootstocks which create small trees, is an ideal rootstock for dense plantings and making cordon apples, which is one form of tree training. However since it has shallow and weak roots, it needs soil that is rich in nutrients. Moreover, during dry spells, you will need to water regularly and also weed it. If you would like to grow your tree as a small bush, the tree will still need support because of the shallow root structure. There have been many clones of M9, including M9.337 which is the virus free stock. The original M9 has low replant resistance and is susceptible to fire blight and woolly apple aphid. It does have high crown/root rot resistance.
Geneva 11 (or G.11) is an excellent replacement for M9. Although it does really well in loam and clay-loam soils, it is not as tolerant of sandy soils. Although G.11 has replant, crown and root rot resistance, and moderate resistance to fire blight, it is not woolly apple aphid resistant.
This dwarf variety is a cross between M27 and Robusta 5. Not only is it highly resistant to fire blight and phytophthora, but may also be tolerant of replant disease. After five years, it produces trees similar in size to M.9, but it has higher yield efficiency and produces few root suckers.
Although G.214 is not yet widely available for purchasing, it has fire blight, woolly apple aphid, and replant resistance.
G. 16, a cross between Ottawa 3 and Malus floribunda, is very precocious with a productivity similar to M9. Additionally it is resistant to fire blight, crown and root rots, but susceptible to woolly apple aphid. Moreover, similar to all other dwarf rootstock, it requires full tree support.
Semi-Dwarf Apple Tree Rootstock 8-12ft
Note: When planting trees on semi-dwarf rootstocks, you can plant them generally about 10-12 feet apart.
While G.935, a cross between Ottawa 3 and Robusta 5, is the most precocious of the Geneva series, some of the plantings are under decline. Therefore it is good to be cautious with this rootstock until researchers understand the reason for its decline. Although it is not resistant to woolly apple aphid, it does have fire blight and crown rot resistance.
G.210, a cross between Ottawa 3 and Robusta 5, has resistance to fire blight and crown rot. While it is similar in size to M7, it is also more productive and precocious.
While the size of the G.969 rootstock has varied in different trials, it does have fire blight, crown rot, and woolly apple aphid resistance. Additionally, in these trials, it was noted as one of the best in the Geneva family.
G.202, a cross between M27 and Robusta 5, is a semi-dwarfing rootstock with resistance to fire blight, phytophthora, and woolly apple aphid. Overall G.202 produces good quality trees.
G.30, a cross between M9 and Robusta 5, has a precocity and productivity similar to M26 while also having a high resistance to fireblight and good resistance to crown and root rots. However, it is susceptible to woolly apple aphid.
M26, a cross between M16 and M9, is one of the more vigorous dwarfing rootstocks. Since it was created in 1929 at the East Malling Research Station, it has been used widely all over the world. However while M26 is precocious and very productive, it is susceptible to crown rot and fire blight.
Semi-Standard Apple Tree Rootstock 10-16 ft
Note: When planting trees on semi-standard rootstocks, you can plant them generally about 15 feet apart.
G.890 is one of the semi-standard rootstock that is also resistant to fire blight, crown rot, and woolly apple aphid. Additionally it is more precocious than Malling rootstocks with similar vigor.
MM111, a cross between Merton 793 and ‘Northern Spy whose virus free clone is EMLA 111, produces a tree about 80-85% the size of a standard tree. It is not only resistant to woolly apple aphid but is also tolerant of fire blight, crown and root rots. Additionally it’s winter hardy.
Bud. 118 (also known as Budagovsky 118 or B.118) produces very cold hardy trees about 85% the size of a seedling. However it is more precocious than a seedling. Additionally it is moderately resistant to fire blight and crown rot.
MM106, also known as Malling-Merton 106, produces trees around 60-70% of the standard size so around 12ft tall. However you can prune the tree to a smaller size. In addition to being precocious and productive, it is also resistant to woolly apple aphid. However it is susceptible to collar rot. Moreover it doesn’t require support after it is established. Its virus free clone, EMLA 106, is now very popular among growers.
Standard Apple Tree Rootstock 14-20ft+
Note: When planting trees on semi-standard rootstocks, you can plant them generally about 30 feet apart.
P.18 (or Polish 18) produces trees with a standard size (20ft+). The Research Institute of Poland in Skierniewice, Poland created this from a cross between M.4 x Common Antonovka. When it was tested in North America, it was less precocious and had lower yield efficiency than MM111. Some tests also showed that it is moderately resistant to phytophthora. However P.18 is susceptible to woolly apple aphid and moderately susceptible to fire blight. Additionally, it produces few root suckers and burr knots.
The Antonovka seedling produces very healthy, vigorous, and long-lived trees. Additionally these trees are the most drought-tolerant and adaptable to different soil types. Although with varieties the tree will bear only after 4-6 years, with others, such as Anna, Dorsett Golden, and Shell of Alabama you can see fruit in 2 years.
M25 produces trees with a standard size of 20ft+. Many cider apple orchards use M25. Researchers developed this rootstock in the 1950s as a cross between the original Malling M2 rootstock and the American Northern Spy apple variety.
How to Select a Rootstock
When choosing a rootstock, some considerations for growers are how well the rootstocks adapts to your soil, the disease pressure on your site, how well the rootstock anchors, and what size tree is optimal for your site. Moreover, a rootstock that grows well in one location, may not grow well in another. Therefore you must also consider your specific site considerations before choosing a rootstock. Other considerations are enhanced productivity and precocity (bearing at a young age).
From our experience growing in New York, we have found the Budagovsky, Geneva, and EMLA series to be great options since they are virus free and produce very healthy trees. According to Scott McDougall and Tom Auvil, who worked at the Washington Tree Fruit Research Commission, the G.41 is especially great as an all-around rootstock. Not only does it have replant, fireblight, and woolly resistance but it also performs well in different soil types. However the union where the scion meets the rootstock can be easily broken on a windy day so it will need support.
For growing standard trees we recommend Antonovka rootstock since they produce very healthy, vigorous, and long-lived trees. Additionally these trees are the most drought-tolerant and adaptable to different soil types.