Layering is a propagation method that encourages new roots to form on branches still attached to the parent plant. The parent supplies the layer ― the new plant ― with water and nutrients during the rooting process.
Also called simple layering, ground layering is an easy way to produce a few new plants, though it may take as long as a year. Some plants, such as trailing blackberry, reproduce naturally by ground layering. Numerous others are well suited to this method, among them forsythia, gooseberry, grape, hazelnut, mountain laurel (Kalmia), rhododendron, rose, spiraea, and lilac (Syringa).
To ground layer, follow these steps:
1. In spring, select a young, healthy, pliable shoot growing low on the plant to be layered. Loosen the soil where the shoot will be buried and work in a shovelful of compost. Dig a shallow hole in the prepared area.
With a sharp knife, make a cut where the shoot will touch the soil; cut about halfway through the shoot, starting from the underside. Dust the cut with rooting hormone powder and insert a pebble or wooden matchstick to hold it open.
Lay the shoot (the layer) in the hole and fasten it down with a piece of wire or a forked stick. Some gardeners tie the layer's tip to a stake to help it grow upwards.
2. Fill in the hole, firming the soil around the layer. A rock or brick can be placed on top to help hold the layer in place.
During the growing season, keep the soil around the layer moist. Adding a few inches of mulch will help retain moisture.
When you are sure roots have formed (this may take anywhere from a few months to more than a year; gently dig into the soil to check), cut the new plant free from the parent. Dig it up, keeping plenty of soil around the roots, and move it to its intended location.
Air layering involves the same principle as ground layering, but it's used for branches higher on a plant. It is often employed to propagate large house plants (overgrown rubber plants, for example), but it's also successful in some outdoor shrubs and trees, including citrus, witch hazel (Hamamelis), magnolia, and rhododendron.
If layering is successful, roots will appear in the sphagnum moss after several months; you can then sever the newly rooted stem from its parent and pot it or plant it out. At this point, it's usually a good idea to remove about half the new plant's leaves, to prevent excessive moisture loss through transpiration while the new plant gets established on its own.
If no roots form, the cut you made will form a callus, and new bark will eventually grow over it.
Air layering is most successful if done while a plant is growing actively. To encourage such growth in houseplants, fertilize the plant to be layered, then place it in a sunny window. When new leaves appear, proceed with layering.
Begin below a node. Make a slanting cut (insert a wooden matchstick to keep it open) or remove a ring of bark. Dust cut with rooting hormone, encase in damp sphagnum moss, and cover with plastic wrap to keep moss moist.