The following lists rootstocks in ascending order of size, smallest first. The numbering scheme for rootstocks does not run in an intuitive sequence!
Whilst most authorities quote the mature size and spread of a tree (as do we) when comparing rootstocks, it is not necessarily as simple as that. An apple tree on M9 can readily grow to the same height as a tree on MM106 if you let it or encourage it. However the M9 tree will have far fewer branches than the MM106 tree, and the branches will not be as thick or have as many secondary branches, and will not form as dense a canopy of leaves in the summer.
The most dwarfing of all apple rootstocks, produces a tree which will be about the same size as a person standing with their arms slightly spread out. Some authorities suggest that M27 is "difficult" because it is so small, but in our experience growing M27 apple trees is straightforward provided you attend to their needs - they benefit from a bit more attention to watering and mulching and weed suppression than more vigourous rootstocks.
The great thing about M27 is that it allows you to grow a lot of different apple trees in a small space. This means you can choose varieties that crop at different times, to get a spread of ripe apples throughout the season. You could plant 5 trees in a row 7m x 1m or 10 trees in a space 7m x 3m - the same space that you would need for one "traditional" standard apple tree. The yield depends very much on the variety and conditions, but you should get 4-5kg of apples per tree - equivalent to 5-7 supermarket poly bags.
Apple trees on M27 also have another interesting characteristic. Unlike every other rootstock, these trees are the same scale as humans (all other rootstocks produce trees that are much taller than us). This creates a very different effect in the garden situation because an "orchard" of M27 apple trees does not take over an area of the garden in the way that fruit trees on other rootstocks would.
Advantages: Produces a very small apple tree, reaches its mature size within 2-3 years. Allows you to grow several different apple varieties in a relatively small space. Very easy to manage because everything is within easy reach. Useful for growing in patio containers.
Disadvantages: Needs a permanent stake. Requires regular watering and good soil conditions. Mulch or clear the soil around the tree - do not allow competing plants to get near.
Article: in praise of the M27 rootstock.
Produces a tree of similar size to M27, but with much better fireblight resistance and cold-hardiness.
Widely used by commercial orchards, and also ideal for the garden. M9 was one of the first modern apple rootstocks, released in 1917 as a specific classification of an old French "Paradise" rootstock called Jaune de Metz.. The "Paradise" rootstocks were used in Europe since the the Middle Ages.
M9 is a great choice for most garden and small orchard situations in the UK and western Europe, especially where you want to maximise your crop and range of apples in a small space. The only slight drawback is that each tree will need a permanent stake, but this is a small price to pay for its ability to produce lots of apples in a small amount of space, and from a relatively young age. Apple trees on the M9 rootstock are also easy to look after and pick from ground level - most of the apples are borne on branches less than about 2m / 7ft high. In addition, M9 apple trees generally have spindly branches and are quite compact, so they don't tend to take over or dominate a small garden.
Its close relation with the old-fashioned Paradise rootstocks which were in widespread use before the 1900s means M9 is a good choice for achieving period authenticity in pre-20th century garden projects.
These qualities also apply in the USA, but M9 is not suitable for areas where fireblight is prevalent or zones where winter-hardiness is an issue.
Advantages: Although M9 induces a small dwarf tree, the apples are usually slightly larger than for the same variety on other rootstocks. It also encourages precocity - in other words, the tree will bear fruit at a young age, you should get a few apples in the 2nd or 3rd year.
Disadvantages: Requires a permanent stake. The ground around the tree should be mulched or kept weed free, because it cannot compete with other plants. Not suitable for areas where fireblight is prevalent (i.e. most of eastern USA).
This roostock is in the M9 class, but perhaps slightly less vigorous. It is the one to choose if cold-hardiness (USDA zones 3 or below) is your main requirement as it outperforms all others in this respect. In warmer zones (including all of the UK) other M9 class rootstocks are a bit easier to manage.
A popular rootstock developed at Cornell University in Geneva, New York (Geneva-series). It produces a tree of about the same size as M9 or perhaps slightly more vigorous, but far better suited to North American conditions.
Advantages: Precocious, some resistance to fire blight, woolly aphid, and collar rot
A good alternative to M9 for areas of the USA where fireblight is an issue. Other attributes are similar to M9, but unusually for a rootstock in this size class, trees on G16 may not need a permanent support.
Another good alternative to M9 for areas of the USA where fireblight is an issue. It is probably the most fireblight-resistant of all the M9-class rootstocks.
M26 is a good general-purpose rootstock, which can be used for a wide variety of purposes, from free-standing trees, to cordons and espaliers. Best considered for the same situations as MM106 (below) but where you want a slightly smaller tree, although vigour increases in warmer climates. Avoid planting on soils where flooding might be a problem because M26 has no resistance to collar rot.
Advantages: Produces a good productive tree. Good choice for cordons. Cold-hardy in North American conditions (unlike most of the other Malling-series rootstocks).
Disadvantages: Usually needs a permanent stake, but this need not be as prominent as it is for the smaller rootstocks. Susceptible to fire blight, woolly aphid, and collar rot.
One of the original Malling-series rootstocks, produces a tree intermediate between M26 and MM106. Like M9, M7 was a specific selection of an original "Paradise" rootstock.
Advantages: Popular in the USA because it turned out to have reasonable resistance to fireblight and crown rot - before other rootstocks had been developed specifically for these conditions.
Disadvantages: Newer Geneva series rootstocks are usually more suitable for North American conditions.
G11 / MM111
Whilst most trees have a single rootstock, it is possible to insert an "interstem" - a second piece of rootstock - between the main rootstock and the scion (fruiting) variety. In this case the MM111 rootstock is used, with a grafted piece of the G11 rootstock as an interstem. This results in a well-anchored tree which is somewhere between M26 and MM106 in size.
Advantages: All the benefits of the vigorous MM111 rootstock (good anchorage and suitable for a wide range of soil conditions) along with the precociousness of the G11 rootstock.
This is probably the most versatile rootstock for growing specimen apple trees in Europe, producing a tree of 3m-4m in height and spread, and equally suitable for growing in permanent containers or in various trained forms such as espaliers. It is occasionally used in North America too. Staking is useful after planting (more so if growing in an exposed situation, less so in a garden situation), but the tree will become free-standing within a few years and the stake can be removed. Trees on MM106 do not require much attention apart from watering in dry spells, and once established will tolerate other plants or grass growing around them.
Advantages: The best rootstock for most garden and small orchard situations in Europe, particularly when grown on good soils and well watered. Useful for both free-standing trees and for large fans and espaliers. Does not need staking, and can be left to its own devices once established.
Disadvantages: Whilst much of the crop should be accessible from ground level, you may need a ladder to pick fruit from higher up the tree. Less successful in North America because it is susceptible to fireblight, collar-rot, and is not particularly cold-hardy.
A new rootstock which is very similar to MM106 but produces a tree about 5% larger in some conditions, otherwise about the same size. It was developed in the 1960s from MM106 crossed with M27. Although it is not widely planted yet, it can be considered as an improved MM106, with roughly similar performance to MM106 but adaptable to a wider range of soil conditions.
Advantages: Resistant to Phytophora (the fungus which causes brown rot / collar rot) and woolly aphid. Resistant to re-plant disease.
Disadvantages: Relatively new, so there is less knowledge of its performance with different scion varieties and in different conditions.
A semi-vigorous rootstock, producing trees somewhat larger than MM106, in the range 4m-5m / 14ft - 18ft.
MM111 is well-known for its ability to grow in both heavy and light soils and to tolerate drought and damp conditions.
Advantages: Doesn't require much looking after, and ideal for growing traditional large apple trees.
Disadvantages: Can take many years (5+) before fruit is produced in quantity.
A vigorous rootstock, producing trees somewhat larger than MM111, in the range 4m-6m / 14ft - 20ft.
Advantages: Don't require much looking after, and ideal for growing traditional large apple trees.
Disadvantages: Although B118 is more precocious than MM111, and produces fruit from an earlier age, it is still going to take a decade or more to reach full size.
M25 is the most vigorous apple rootstock. It produces a standard apple tree of around 6m height after 10 years or so, and is the best choice for old-fashioned traditional orchards.
Advantages: Doesn't require much looking after, and ideal for growing traditional large apple trees.
Disadvantages: You will need a ladder and fruit-picking bags to pick the apples - an enjoyable community activity but obviously not without dangers, seek specialist help if necessary.