Apple rootstocks have been developed to provide a tree with predictable characteristics, especially size. These may be modified to some extent by the vigour of the variety that has been grafted on to that rootstock. Rootstocks are numbered, but those numbers do not form an obvious or logical pattern. The rootstock that forms the smallest tree is M27, followed by M9, M26, MM1 06, and M25 or M11 giving trees of increasing size. The characteristics of each rootstock are listed below.
M27 can be described as EXTREMELY DWARFING, producing a tree of about 1.2- 1.8metres (4-6 feet). It is useful for trees to be grown in pots as patio fruit and also for reducing the vigour of triploids such as Bramley’s Seedling. This rootstock requires good soil and will not stand neglect or competition from weeds or grass. It needs continuous support and is often shorter lived. The trees will come in to fruit in between 2 and 3 years.
M9 is described as VERY DWARFING, producing a tree of about 1.8- 2.4metres (6-8 feet). The main problem with this rootstock is that it has brittle roots, and even when staked, has a tendency to blow over. The trees can be pulled upright again and stabilised using a tripod. This rootstock tends to be the main one used for trees available in Garden Centres. These trees come in to fruit in about 3 years, but do need careful staking and will not withstand competition from grass or weeds.
M26 is DWARFING producing a tree of about 2.4-3metres (8-10 feet). It is a useful general purpose rootstock, and can be used to produce most of the tree forms such as bushes or cordons but not espaliers, however it does need continuous staking. Trees on this rootstock will grow in most soil types, and come in to fruit in 3 to 4 years. Experience has shown that it is not always a good choice for northern gardens.
MM106 is SEMI DWARFING producing a tree of about 3-4 metres (10-13 feet). It can be used for most purposes, including all trained forms. It only needs staking for the first few years until the root system is well established. This rootstock will grow in most soils, even light ones. The trees come in to fruit in 3 to 4 years.
M25 or MM111 are VIGOROUS rootstocks, producing trees well over 4.5 metres (15 feet) tall. These rootstocks are used for trees in grazed orchards. They will grow in most soils and take about 5 years to come in to fruit. They may need staking for the first few years.