Air layering is a plant propagation technique which involves wounding a branch and stimulating it to produce roots, and then cutting off the branch and planting it. While this process may sound slightly strange, it has been practiced for centuries, and in its native China, air layering is a widely used method of propagation. This technique can be used for woody ornamentals, some trees, and many houseplants, and it is relatively easy to do, even for novice gardeners.
Gardeners usually decide to air layer a plant when they plan to trim away a branch or piece of growth anyway. The logic is that the healthy branch may as well be turned into a new plant and removed, rather than being trimmed and thrown away altogether. People may also utilize air layers to make clones of favorite plants and cultivars. People who work with bonsai are especially fond of this propagation technique, since the cultivation of bonsai is already heavily controlled.
People can air layer in the spring after the plant's leaves have fully established themselves, using a branch from the previous season or year's growth, or in the summer, using a branch which grew during the spring. Generally, a branch of at least pencil size is necessary for successful air layering.
The process starts with removing the outer layers of bark to girdle the branch. The goal is to allow nutrients to flow up the branch so that it does not die during the air layering process. In some plants, rather than girdling the branch, a deep slit is made and held open with a wedge. In either instance, the next step involves wrapping the injury in damp moss, and then enclosing the site with a plastic cover which will keep it moist. Some people use potting soil instead of moss, and many wrap the plastic in foil to reflect heat so that the developing roots are not cooked in the plastic.
It can take three to six months for roots to develop. The air layering process is generally considered done when a network of roots can be clearly seen inside the plastic. At this point, the branch can be severed below the root ball, and planted. Some people provide the plant with root stimulating hormones at the beginning of the process or during the planting phase to promote the rapid development of a root ball.
The new plant is usually very fragile, and it needs special care to encourage the small root ball to develop and support the plant. Some gardeners surround the plant with a plastic bag to keep it moist, or store the plant in a warm, humid environment such as a greenhouse while it establishes itself. Growth above the ground is often minimal during the first season or two, as the plant sinks much of its energy into making healthy roots.