Layering is basically a method of getting a branch or stem to produce roots while still being attached to the parent plant. When the roots are established, the branch is cut and the new plant is potted or planted into the ground where it starts growing as a new plant. This is a method of propagation that is asexual, or vegetative rather than sexual, as is the case when propagating from seed. Two main benefits of asexual or vegetative propagation are: New plants are capable of reaching maturity much faster than when propagated from seed. When layering though, it may take a long time for roots to start growing in some species. Some plants such as hybrids will not reproduce true to parent stock when propagated from seed, in fact, some of these kinds of plants will not even produce viable seed. Asexual propagation in such cases is the only way to get new plant starts.
Propagating by layering, in its simplest form, is accomplished by bending a low growing branch of a tree or shrub to make contact with the ground. At the point where the branch touches the ground the branch must be secured. It can be tied down with stakes and partially buried with soil, or it can be weighted down into loose soil by placing a stone, brick, or block over it. Anchoring it down with wooden stakes or hardware hooks is best. Pruning the parent plant a bit will usually stimulate growth in the lower branches of a plant. In some cases, where the branch is long enough, contact with the ground can occur at several points along its length, resulting in several new plants from one branch. This is known as compound layering. Roots can be coaxed to grow from the low growing branch branch by cutting away a 1 or 2 inch strip of bark from the side that faces the ground. Apply some rooting hormone powder to this wound and secure the branch to the soil. If compound layering, repeat at several points along the branch.
The best season for layering is early spring. Layering can be done later in the year, but if there is not enough time for roots to form during the current season, the propagation will not be complete until the following year.
Many species of house plants can be propagated in the same way. Bend a stem, branch, or vine over to another pot (or pots) and new roots will begin to grow there.
In some species of plants, such as many kinds of berries, layering is done from the tips of the canes rather than along their sides. In mid summer, bed the canes over until the tips come in contact with the ground. The ground at these points should be softened up with a spade or you can use pots about 8 inches deep full of potting soil. These cane tips should be buried no more than 6 inches deep. After new plants have sprouted and established their own roots, the connecting canes can be severed. The new plants will still have several weeks to develop before winter.
Many kinds of deciduous shrubs, roses and fruit trees that are not more than 4 feet high can be layered in mounds of dirt. "Stool Layering" is accomplished by cutting back the main leader or trunk of the shrub to within 2 or 3 inches from the surface of the ground in late winter or early spring before the plant begins its new growth. This method works best if the plant has been heavily pruned the preceding autumn. New shoots will start to grow just below the top of the stump. Pinch off any buds that occur to stimulate more of these shoots to start growing. When these new sprouts are about 6 inches tall, get some rich garden soil and bury the stump and the base of the new shoots leaving only the top leaves exposed. As these shoots grow, continue adding more soil until a mound (stool) nearly a foot high is covering all but the top leaves. Mulch heavily with dried leaves, bark or lawn clippings to retain moisture within the stool. After several weeks, each shoot will develop roots. Sever the stem connecting them to the parent plant and transplant to new location or to individual pots.
Another method, similar to Stool Layering, is to cut the entire plant back to within a few inches from the ground the preceding autumn. In early spring new shoots will start to grow from just below the severed top of the stump. When these new shoots are 6 or 8 inches tall, dig up the entire plant and bury deeper into the ground until only the tops of the new shoots are exposed. Use a fine rich garden soil to back fill around these new shoots. Each of these shoots will grow there own roots and can be transplanted once they are will established, by the end of summer.
Air Layering is accomplished by cutting away a half inch strip of bark all the way around an upper branch. Apply a rooting hormone powder to the exposed wood and wrap some damp sphagnum moss around the area. Wrap the sphagnum moss with a 5 or 6 inch wide strip of black polyethylene plastic and secure it above and below the area with electrical tape or duct tape. Allow the plastic to balloon out to offer space for the new roots to grow. After the new roots are well formed, cut just below the area to sever from the parent plant. This is a great way to obtain bonsai specimens. Plant in pot or in the ground.