Nearly all commercial apple trees are grafted or budded onto rootstocks, which determine the size of the eventual tree. Knowing which rootstock is needed, and matching it to the soil and the size you want, enable a tree to be productive and healthy.
Most of the important rootstocks for apples were derived from material collected by East Malling Research Station, UK, in the early 1900s. Researchers collected and characterised the stocks developed by growers during the preceding centuries in Europe. Each one was given a number, preceded by M.
In 1917 The Malling Research Station joined forces with the John Innes Institute at Merton to breed some aphid-resistant rootstocks: the MM101-115 series.
A later development has been the cleaning up of some of these stocks (in conjunction with the Long Ashton research station) to produce virus-free stocks. These are prefixed by the letters EMLA (East Malling – Long Ashton).
In the notes below, M denotes a Malling rootstock, MM denotes a Malling-Merton hybrid.
M27 – Very small indeed, around half the size of M9. Tree needs full support. Fruit size reduced slightly. Moribund in wet soils. Very little pruning is required once the tree is full size (around 5ft/1.5m high; producing perhaps 20 apples a year). It’s OK in pots.
M9 – The best known dwarfing rootstock. It is a cross between a French tree, “Jaune de Metz”, and the “Paradise” apple of ancient Persia. It is known as the “Paradise” stock of Europe. It fruits when very young, is fairly hardy, tolerant of wet but not drought, and compatible with all apple scions. It has to be staked strongly, its roots are slightly brittle, and it is about 8-9ft/2.4-2.7m tall at maturity on an ideal soil.
M26 – A cross of M9 and M16. Used in irrigated orchards on well-drained solis. Fruits early in its life, needs permanent staking, hardy. Susceptible to crown rot and fireblight. M26 is not so good in wet, clay soils where it is rather moribund. Produces burr knots – the beginnings of little aerial roots – which attract pests and which can compromise the tree. These can be sliced off carefully in the garden situation. Planting deeper (so less rootstock is exposed) helps solve the problem commercially. Reaches about 8-10ft/2.4-3m if unpruned. OK in pots.
MM106 – A hydbid of Northern Spy (English dessert apple) and English Broadleaf. Well anchored, fruits early in its life, few suckers, fruit matures late, trees have a long season, OK in pots with less vigorous varieties. Susceptible to crown and root rot. Recommended as a substitute for M26 in wet, cold soil as a little more vigorous. Semidwarf. 9-11ft/2.7-3.3m high. Resistant to woolly aphid.
MM111 – Northern Spy hybrid. About 75% of full size; too large for small gardens. Prone to burr knots. 10-12ft/3-3.6m. Semi-dwarfing or half-standard. Resistant to woolly aphid.
M2 – Very similar in size and vigour to MM111. Not quite so vigorous as M25.
M25 – Full size tree; avoid unless you have a large space in which to grow it. Very vigorous; typically 12-15ft high; can be bigger depending on variety; large, heavy, spreading tree.
SEEDLING TREES – OWN ROOTS
Trees grown from pips are usually M111 size or larger and extremely hardy. Some decorative crabs on their own roots are about the size of MM106 but others (especially native English green-fruited crabs) are enormous.
Colt – Semi vigorous – 13-16ft/4-5m. Fully compatible with all varieties, Considered very productive until the arrival of Gisela; still good for bush and half-standard cherries on thin soils.
Gisela 5. – Dwarf, 40% of height of Colt. Ideal for commercial orchards, gardens and patio pots.The best garden choice for Cherry Trees.
Compatibility – it should be noted that there are many incompatible varieties when grafted onto Quince (especially Quince C). In these instances a suitable interstock should be used such as Beurre Hardy or Doyenne du Comice. The latter will also impart some resistance to Fireblight.
Pyrus communis (Seedling pear) – Very vigorous. More suitable for half standard and especially standard trees.
Quince ‘A’ – Semi Dwarf. The ideal rootstock for bush trees.
Quince ‘C’ – Dwarf and slightly earlier into cropping.
Pyrodwarf – Limited availability as yet but this one is proving more compatible with Perry pears and others
Rootstocks for Plums, Gages, Damsons & Mirabelles
Brompton – Vigorous, very suitable for standards, does not sucker and fully compatible with all varieties unlike its predecessors such as Myrobalan.
St. Julien ‘A’ – Semi vigorous. This is fully compatible with all plums, damsons, gages, peaches, nectarines and apricots and many ornamental prunus species. Good yield influence. Not suitable for poorly drained soils.
Pixy – Dwarf and ideal for size containment in the garden. On very strong soils it still has commercial use for strong growing, shy cropping varieties such as Marjories, Avalon and Excalibur. Not recommended for Victoria.