This method stimulates root formation in plants that are difficult to grow from cuttings and that have stiff, upright stems that cannot be layered by being brought down to soil level. If a houseplant such as a rubber plant, codiaeum or dracaeana becomes unattractive as a result of losing its lower leaves, air layering can help to rejuvenate it. The aim of this procedure, as the name suggests, is to stimulate rooting at some point on the stem without lowering the stem to the surface of the potting mixture.
The first step is to wound the stem at a point below the lowest healthy leaf, preferably no more than 3 or 4 inches below it. One way to do this is to make an upward slanting, inch long cut with a very sharp, thin-bladed knife. The cut must not go beyond the center of the stem. Force open the cut just enough for the insertion of a small piece of matchstick or a grain of coarse sand. Cutting the stem in this way, unfortunately, weakens it, so that the top may break off if the plant is accidentally jostled. Many experienced growers prefer a less risky method: using a sharp blade, scratch out two fine rings a half-inch apart in the bark or skin and peel off the area between the rings. This type of wound will leave the inside tissue of the plant undisturbed.
The next step is to dust the cut surface of the stem lightly with a rooting hormone (powder), then surround it with a double handful of moist sphagnum moss. Wrap the narrow end of and oblong sheet of plastic around the stem. A plastic bag cut down the sides will do the job as long as it is big enough for the ends to overlap. Tie the bag at the base with stout thread or secure it with insulating tape. Then fill the bag with the moistened moss and secure the top of the bad around the stem to keep the moisture from escaping.
After a number of weeks, white roots should appear on the outside of the moss within the plastic covering. When the roots are visible, remove the plastic and sever the stem with a sharp knife, making a horizontal cut immediately below the ball of moss. Plant the new root ball in a pot large enough to allow about a half-inch of potting mixture to be worked in around all sides of the mossy root ball. Treat the plant as a mature specimen. If necessary, use a support stake. The original stem need not be discarded. It should sprout again, usually near the top. When the new plant has been cut away, it is often wise to cut the old stem back to a point where new growth will make a more compact specimen. As long as the stem remains leafless, give the plant only enough water to make the potting mixture barely moist, allowing the top two-thirds of the mixture to dry out between watering. After new growth appears, increase the amount of water and begin to fertilize the plant.
If desired, the bare stem of a plant such as a dracaena that has been air layered can be cut into 2-inch lengths for use as stem cuttings.