Nearly all commercial apple trees are now 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, enables a tree to be productive and healthy.
There is no other fruit crop where so much attention has been devoted to roots. There are about 20 well-known rootstocks for apples. Some of them can be traced back hundreds of years.
As well as the choice of stock, the depth of planting
affects rootstock vigour. The higher the graft, or the shallower you
plant it, the less vigorous the tree. Remember this especially if you
are putting trees in pots: graft higher up.
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. If you come across these, they 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.
There are others, which more or less match the Malling
or Malling-Merton rootstocks, from overseas. They include G (from the experimental station
at Cornell, Geneva, NY), P (Poland), Bud (Budagovsky programme) and Antonovka (from Russia), O
(from Ottawa) and Mark (from Michigan).
Here's a list of the English rootstocks which are well-known,
smallest to largest:
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 high; produces perhaps 20
apples a year). It's OK in pots.
It's susceptible to tomato ring spot virus.
The best known dwarfing rootstock. This is the rootstock used at Brogdale, UK, for the National Fruit Collection. 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 8-9 feet tall at maturity on an ideal soil.
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 if unpruned.
OK in pots.
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
by my supplier as a
substitute for M26 in wet, cold soil : a little more vigorous.
Semidwarf. 9-11ft high.
Resistant to woolly aphid.
Descended from a French tree, "Doucin Reinette". Very hardy. Likes deep, well drained soils. It suckers badly, is prone to crown gall, is resistant to fireblight, and tolerates wet soils. About the same size as MM106 (semidwarf). Has been used in New Hampshire, USA for 40 years. Fruits in 5th year. Has a tendency to lean. Most trees are very fruitful. Needs staking for first 4-5 years.
Northern Spy hybrid. About 75% of full size; too large for small gardens. Prone to burr knots. 10-12ft. Semi-dwarfing or half-standard. Resistant to woolly aphid.
Very similar in size and vigour to MM111. Not quite so vigorous as 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 MM106 size (occasionally 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 - I've seen one in Burbage woods,
Leicestershire, 30ft high and with a trunk 2 ft in diameter.
Typical Use of Rootstocks:
Deacons, of Godshill, Isle of Wight, supply all of their trees on EMLA
rootstocks -M27, M26
or M25. It can be argued that these are the only stocks you need.
They recommend the use of M27 as stepover trees (single
tier espaliers) and in pots.
M26 is their main stock - for fans, bushes, pyramids, cordons and they
reckon staking is only necessary in an exposed situation. MM106 is the
most widely planted stock for bush trees in commercial orchards; also
OK for fans and cordons and Ballerinas (pole trees). M25 is "the best half standard rootstock as it induces
early fruiting - unlike the old type half standard, which took years to fruit".
Deacons also do family trees - two to six varieties on one
stem - using
M26 and M27. Are they the world's experts on this type of
tree? I have found no-one else who sells them.
There are some
American sites which give very comprehensive discussions of the
strengths and weaknesses of different rootstocks - including the ones from Poland,
Cornell, Michigan, Russia, Ottawa, etc. Using Google and entering ROOTSTOCKS will
take you straight there.
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