Why does the neighbour's apple tree reach three metres and bear basketfuls, while another of the same variety grows into a giant you can barely pick? The difference is not in the variety but low down on the trunk: in the rootstock.
Almost every fruit tree on sale is grafted. Understanding what that means lets you buy more deliberately and avoid the most common mistake in the orchard, namely the far too large tree in the far too small spot.
Two plants in one tree
The rootstock is the rooted part. A shoot of the desired variety, the scion, is set onto it. The two fuse at the graft union, the swollen seam just above the soil. From then on the variety supplies leaves, flowers and fruit, the rootstock supplies the roots and the growth rate.
This is done because many fruit varieties cannot be grown true from seed, and because the rootstock brings qualities the variety alone lacks: a defined final size, hardy roots or tolerance of heavy soil.
What the rootstock controls
Four things the rootstock decides
- The final size
From the knee-high potted column to the stately standard, the rootstock alone decides how big the tree ends up.
- When cropping starts
Dwarfing rootstocks bear early, often in the second or third year. Vigorous rootstocks take their time but then crop for decades.
- Stability
A dwarf tree on a weak rootstock has little root mass and needs a permanent stake. A standard stands on its own.
- Soil and drought
Some rootstocks cope better with heavy or dry soil. In difficult spots the right rootstock is half the battle.
The key apple rootstocks
On apple the names are standardised and usually printed on the label. A rough guide:
- 'M27' and 'M9': very weak to weak. The spindle tree for small gardens and rows, early cropping, always needs a stake and good soil.
- 'M26' and 'MM106': semi-vigorous. The classic bush tree, easy to pick, often the sensible choice for the home garden.
- Seedling and 'M25': vigorous. The standard for the traditional orchard meadow, grows large and old, crops later but over generations.
On pear the same principle runs through quince rootstocks (weaker) and seedling (vigorous), on cherry through the 'GiSelA' types that finally make the once-huge trees pickable.
Choose the variety by taste, the rootstock by the space. Both belong together before the tree goes into the trolley.
The core rule on rootstocks
Frequently asked questions
What is a rootstock on fruit trees?
The rooted part of the tree onto which the actual variety is grafted. It mainly sets the final size, the age at first cropping and the stability. The same apple variety comes as a dwarf or a giant depending on the rootstock.
Which rootstock suits a small garden?
On apple a weak one such as 'M9', giving an easily picked tree of about two to three metres. It bears early and needs little space, but a permanent stake and regular water.
How do I recognise the rootstock when buying?
Usually it is on the label next to the variety, for example "Elstar on M9". If the detail is missing, ask the nursery. Without a rootstock label you are buying a pig in a poke as far as size goes.
Why does a dwarf tree need a stake?
Weak rootstocks form little root mass. Loaded with fruit, the tree cannot hold itself and would topple in wind. A stake reaching to just below the crown stays permanently on these trees.
Can I change the rootstock later?
No. The rootstock is fixed at purchase and does not change. What you can influence is the tree form through pruning, but the basic vigour is set by the rootstock.
