Keep soil moist. When roots have formed sever stem from parent, bury in rich soil and keep moist. Daphnes, Japanese tree lilacs, and shrub and climbing roses all respond well to this process. Tall trees and shrubs are difficult to layer because they do not have branches long enough to reach the ground, or stems that are too rigid to be bent. Often it is possible however, to root these high branches by bringing the earth to them in a method called air layering.
Air layering is a technique invented by the Chinese four thousand years ago.
They would place a pack of wet soil around an upright growing limb, wrap it in cloth and keep it moist until roots formed. The ancient method was later improved upon, and with the invention of plastic to hold and seal the medium, air layering became a method easy for even a beginning gardener. Air layering can be done at any time, but it is best to do it in early spring. The best place to position an air layer is on the new growth of the upper branches, and leaves should always be left on the branch. Make a slit on a branch about 12 inches from the tip and insert a matchstick to keep it open.