Certain species of plants do not develop roots rapidly enough to be propagated by cuttings. In these cases, the stem dies from lack of water and nutrients before the roots can be initiated. Layering permits the stem to remain partially attached, receiving water and nutrients through the still intact vascular system, while initiating roots at the point where separation from the parent plant will eventually occur.
Compared to other methods of propagation, layering is usually slower, more expensive, and produces fewer new plants per parent plant. For reproduction of large numbers of the most common nursery and greenhouse crops, layering has limited use. Amateur horticulturists use the techniques frequently when quantity is not important. Specialty nurseries use layering for unusual or rare species that do not reproduce from cuttings. Landscape gardeners whose professional efforts are directed to a single landscape such as an estate, cemetery, or school campus also use layering techniques.
Successful layering depends on treatments applied to the stem to create an accumulation of carbohydrates, auxins, and other organic materials in the layered region. The treatments commonly applied to the stem include:
• elimination of light in the region where rooting is desired
• intentional injury or girdling where rooting is desired
• application of growth substances to promote rooting
• provision of a rooting medium that is well-aerated, moist, and of a consistent and moderate temperature