For some shrubs, taking cuttings is not successful as propagules may die before new roots can be formed. In these cases, layering is another option.
Layering is a form of propagation where new roots are formed on vegetative pieces (primarily stems) while the propagule is still attached to the parent plant. This form of propagation produces propagules that are genetic clones so your propagule will be the exact same plant as the parent plant with the same flower color, form, and other attributes. This form of propagation can be time-consuming, but because plants are supported by the parent plant while developing new roots, it is relatively low stress on the plant and has a good rate of success for home gardeners.
There are several methods of layering. The method best used depends on the species of plant and not all species are propagated by layering. Many shrubs are successfully propagated by air layering, simple layering, or tip layering.
When to Propagate | Rooting Hormones | Simple Layering | Tip Layering | Air Layering | More Information
When to Propagate
Early spring while the plant is still dormant through mid-summer is the ideal time to propagate by layering. Some plants will root quickly and be ready for transplanting by early fall and other species may take several growing seasons to fully root and then be separated from the parent plant.
Rooting Hormones
Rooting hormones are sometimes applied to stems being layered to promote root formation.
The two synthetic auxins most frequently used are IBA (indolebutyric acid) and NAA (naphthaleneacetic acid). Various concentrations are available. Consult the label to determine the appropriate concentration based on the species of plant you are propagating.
For layering, use powder forms as liquid forms are difficult to apply. Start by placing a small amount of powder in a separate container or on a paper plate or towel. Never return leftover material to the original container or use rooting hormone directly from the original container, as disease issues can easily be spread this way.
To apply, dust the damaged area with the powder. Do not over-apply. Too much rooting hormone can sometimes slow root development.
Store rooting hormones in their original containers in a cool, dark location. After approximately two years, their efficacy drops sharply and should be replaced.
Simple Layering
Simple layering works well with plants that have long flexible stems. The propagule is formed by pinning and/or burying a portion of the stem, waiting for new roots to form, and then cutting it from the parent plant. By bending and burying the stem, it slows and interrupts the downward translocation of carbohydrates and other compounds. The accumulation of these compounds at the bend promotes rooting.
How to Propagate by Simple Layering
- Bend or stretch a stem or branch down to the soil
- Bury the stem 2-4 inches deep, bending the tip of the branch up out of the soil. Make sure at least one (if not more) node is buried.
- Do not bury leaves. Remove any leaves that would be buried in the rooting media
- If needed, pin the branch with landscape pins or bent wire to help hold it in place
- Try wounding the branch and dusting it with rooting hormone powder before burying it for faster root development
- New roots should form in 6 to 12 weeks (maybe longer, depending on the species)
- When adequate roots have formed, the stem will be firmly rooted into the soil. Cut or separate it from the parent plant, dig up the propagule, and transplant it to its new location.
Species Propagated by Simple Layering
- Forsythia
- Climbing Roses
- Honeysuckle
- Azalea
- Rhododendron
- Boxwood
Tip Layering
Tip layering works well with some species with long flexible stems. The propagule is formed by burying the tip of a long flexible stem, waiting for new roots to form, and then cutting it from the parent plant. When the tip is buried, it starts pointed downward and then begins to grow upward. The bend created slows and interrupts the downward translocation of carbohydrates and other compounds. The accumulation of these compounds at the bend promotes rooting.
How to Propagate by Tip Layering
- Bend or stretch a stem or branch with current year's growth down to the soil
- Bury the stem tip 3-4 inches deep.
- If needed, pin the branch with landscape pins or bent wire to help hold it in place
- New roots and a new shoot should form in 6 to 12 weeks (maybe longer, depending on the species)
- When adequate roots have formed, the stem will be firmly rooted into the soil. Cut or separate it from the parent plant, dig up the propagule, and transplant it to its new location.
Species Propagated by Tip Layering
- Raspberry
- Blackberry
Air Layering
Air layering is a procedure used to induce roots to form on a plant stem while it is still attached to the parent plant. It is particularly useful for those plants without flexible stems. Complete or partial girdling of the plant stem interrupts the downward translocation of carbohydrates and other compounds. The accumulation of these compounds promotes rooting at the point of injury.
How to Propagate by Air Layering
- Select a point on a stem about 12 to 18 inches from the shoot tip. Remove any leaves in the immediate area
- Wound the plant at this location
- Using a sharp knife, cut completely around the stem. The cut should penetrate down to the woody center of the stem
- One inch below the first cut, make a second cut completely around the stem
- Make a third cut connecting the previous two cuts. Remove the ring of bark.
- Scrape the exposed surface to insure the complete removal of soft (cambial) tissue
- Dust a small amount of rooting hormone on the exposed surface or by pushing it into the cut
- Place one or two handfuls of moist sphagnum moss (un-milled) around the exposed area
- Wrap a piece of clear plastic (such as a cut-up plastic sandwich bag) around the sphagnum moss. Make sure none of the moss protrudes out the ends of the plastic wrap. Secure the plastic above and below the sphagnum moss with twist ties.
- Aluminum foil or plastic wrap can be used instead of a piece of clear plastic
- Electrical tape or cotton string can be used instead of twist ties
- Roots should appear in the sphagnum moss in several weeks. Although for some species it could take several months
- Monitor the sphagnum moss and add moisture should it dry out (it feels dry to the touch and gets lighter in color)
- If dry, remove the top twist-tie and pour a little water on the sphagnum moss so that it is fully wetted again
- When a good root system has developed, it will be readily visible in the sphagnum moss with roots several inches long. Cut off the stem just below the bottom twist tie.
- Remove the twist ties and plastic sheet and plant the propagule in its new location.
Species Propagated by Air Layering
- Roses
- Azalea
- Rhododendron
- Magnolia
- Holly