pumpkiwi:

The "M" series of rootstocks were developed for specific characteristics of size control and disease resistance by a process of cross-breeding and selection. This particular rootstock series was developed at the East Malling and Long Ashton research stations in England, supported by the British government.

Rootstocks are propagated by a procedure called "stooling". A stem (or stems) are allowed to grow up from the rootstock, then soil is mounded around the newly-grown stem to induce roots to grow in all around it. At the end of the season, the new rootstock can be cut off, above soil level, while the original rootstock beneath remains to produce shoots for future rootstocks. Botanically, this procedure gives the same result as rooting a cutting or air-layering a plant. Suckers that appear from the rootstocks of apple and other trees are also copies of the original rootstock beneath, and can often be used when they have adequate roots.

Seedlings are re-mixtures of genetic material, for rootstocks just as for any apple variety, and will not reproduce the same characteristics as the parents. Most seedling apple rootstocks will grow a very large tree, but there may be some random genetic combinations that would not.

Don Yellman, Great Falls, VA

Just a PS to Don's post:

M-27, called by some a "mini-dwarf," will generally top out at about 6' or so, depending on the vigor of the grafted variety. But it's not well-anchoring and the graft can be brittle, so it needs permanent staking.

M-26 is larger, often about 40-50% of a seedling tree, if I remember.

M-7 is the semi-dwarf "workhorse." About 60-70% seedling height. Widely planted. Well-anchored but prone to suckering.

M-111 is about 70-80%.

Those percentages are off the top of my head, so I may be off a little. There is also a M-9, which is smaller than the M-26, a Bud series (no, not as in beer) as well as new rootstocks from Cornell fruit station in upstate New York named the Geneva series. Each rootstock offers not only size-controlling attributes but resistence to certain insects and diseases, better suitability for various soils and climates, and productivity.

It's often easy to fixate on the dwarfing aspect alone, but, truth is, you can control the size of any tree by agressive pruning and if you choose your rootstock simply for size, you might miss some aspects that would make other choice prehaps better for your climate, soil and location.

Wow. What a long PS. Sorry.

Don

Here's a great link on info about rootstocks:

Here is a link that might be useful: North Carolina Ag Extn

Thanks!