Air layering 6″ thick apple tree branches, can it be done?
Layering is an old method of woody plant propagation whereby a branch on a plant is selected, a section is wounded (sometimes leaf buds are rubbed out or the branch is nicked), and a light moist “soil” is applied and left for a prolonged period of time until roots form at the wound site, and the branch may then be removed from the parent plant as a new “clone” of the original.
Layering can occur naturally or intentionally at ground level in plants such as forsythia, gooseberry, currant and dogwood. Pressed into the ground, the branch is held there for a few weeks (or months), until roots form. Then that section may be removed from the parent plant and relocated.
Air layering functions in more or less the same way, except that a “soil” such as moist sphagnum moss is wrapped around the wounded branch that has no contact with the ground, and this is wrapped with something like plastic cling wrap to retain moisture until roots form.
You would need a young branch (one or two years old) for most active cell growth, so it’s unlikely that a 6″ branch would be a good candidate.
Here is an online tutorial on air layering: