Layering is a plant propagation technique where a stem or root of a plant forms roots while still attached to the parent plant. When root formation is complete, the layered portion is then removed from the parent plant. There are several types of layering including simple, trench, serpentine, stool/mound, tip, and air layering. Air layering is a technique where a portion of the stem is girdled and wrapped in moist sphagnum moss to induce root formation, without burying the stem in soil. It has the advantages of being relatively simple and usually very successful, but requires more time and effort than other layering methods.