Almost all fruit trees are grafted onto a rootstock. This means that the tree is actually two genetically distinct individuals, united by the skilful hand of the grafter. One of these is the rootstock, comprising the roots and the lower portion of the trunk; while the other, known as the scion, is all the rest of the plant: most of the trunk, branches, leaves and fruit. The scion is the fruiting variety, e.g. Cox, Bramley etc. and determines what the fruit is like. Meanwhile the rootstock determines certain characteristics of the tree as a whole:
Size. Rootstocks are classified as vigorous, i.e. full size, or dwarf, with various intermediates such as ‘semi dwarfing’ and so on. (The variety also affects the size of the tree, but to a lesser extent.)
Vigour. Dwarf trees are like infants throughout their lives. Vigorous trees only need to be staked and weeded or mulched for their first 3-4 years and then can look after themselves, but dwarfs need this level of care forever.
Life cycle. Dwarf trees start bearing fruit a year or two after planting and have a short overall life, as little as 25 years for extremely dwarfing rootstocks. Vigorous trees may not start bearing for 8-10 years but can have a productive life of a century or more.
How to Choose Rootstocks
One aim of permaculture is to keep the need for maintenance low, so it might seem that vigorous trees would be the thing. But there are some disadvantages to these big trees:
Yield. A single vigorous tree can produce over 100kg of fruit per year. Can your family eat that much, especially if it’s a non-keeping kind such as a stone fruit or an early-season apple? It may be better to have two or three smaller trees of different varieties.
Space. The most vigorous pears can have a diameter of 20m and apples easily 10m, and you may need two of each for pollination.
Reach. Vigorous trees are tall and all picking, pruning etc. needs to be done from a ladder. A dwarf is reachable from the ground or a little step up.
Life cycle. Most of us want to start harvesting some fruit within a couple of years of planting.
So the advantages of vigour and dwarfness need to be balanced and there are plenty of good stocks that fall in the middle of the size range that combine the advantages of both.
If you want to grow your tree or trees in a restricted form, i.e. the two-dimensional espallier or fan shapes that make such good use of the favourable microclimate up against a wall, you will need to use a relatively vigorous stock. The intensive pruning that goes with this style of growing reduces their vigour anyway. The same goes for fruit trees in pots or other containers: the pot will reduce the size of the root system, so a more vigorous stock is needed to balance this out.
If your soil is poor or your climate challenging, the standard advice is to use a more vigorous rootstock than you would if conditions were more favourable.
M26 is a good stock for medium to large gardens. It makes a tree of 2.5-4m diameter, depending on variety and soil conditions. It's the smallest apple stock that doesn't need staking and mulching throughout its life.
MM106 is ideal for orchards. Diameter is 4-6m and you should get your first fruit within two years of planting.
Quince A is the best all-round stock, giving a tree between 3 and 7m diameter. If you’re short of space you might try the smaller Quince C but only if you can provide the best soil conditions and good care.
St Julien A, at about 3m diameter is the usual choice, with Pixy a slightly smaller alternative.
The problem with cherries is that if you only have one or two trees, the birds will eat all the fruit, so you have to net them. It’s much easier to net a short tree than a tall one and the dwarfing stock for cherries is Gisela.
For more comprehensive information on rootstocks, and much more information about growing fruit, see Patrick’s book How to Make a Forest Garden.
The Minimalist Gardener by Patrick Whitefield
Watch: How to graft a fruit tree