Air layering is a simple propagation technique that was perfected in China more than 4,000 years ago to create offspring that are genetically identical to their parent plants. The process, generally used for small, woody plants, involves wounding the stem, then enclosing it in moistened moss. Roots are produced at the wound site and, once established, the new plant is severed from its parent and potted up.
An excellent method for replicating existing plant material without disturbing the parent plant, air layering has a high success rate, and good-sized specimens can be obtained in a fraction of the time it would take to grow them from seed.
In our Canadian climate, this technique is best carried out in early spring on mature wood from the previous season's growth, 15 to 30 centimetres behind the growing tip. In the case of flowering trees and shrubs, wait until flowering has finished.
Step-by-step guide for air layering
1 Select a healthy, vigorous stem. Trim off leaves and side shoots, leaving just two or three leaves at the growing tip. Girdle the stem by removing a ring of bark about one centimeter wide using a sharp, sterile knife. This enables food and hormones to build up above the girdled section.
2 Dust the girdled area with a rooting hormone that contains IBA (indole butyric acid), which will help to speed up the process. The ideal rooting medium for air layering is sphagnum moss; it holds water, is well aerated and easy to work with; avoid using peat moss, as it doesn’t hold moisture well.
3 After the sphagnum is completely soaked, take two large handfuls, squeeze out the excess water and work into a ball about six centimetres in diameter so the fibres are interwoven. Next, split it in half as it you were dividing an orange. Place the two halves around the girdled area; then weave them together again so the sphagnum remains firmly in place.
4 Take a 20-by-20 centimetre piece of black plastic (industrial-strength garbage bags work well), wrap it around the ball of sphagnum and secure it at either end with strong, weatherproof tape. Then seal the seam along the side with tape.
After four to six months, the layer should have produced enough roots to be potted up on its own (in late summer or early autumn).
Prune back any new growth that the layer has produced during the season. Remove the black plastic and gently loosen the roots and moss; then cut off the stem with sterile secateurs below the roots.
Place the layer in a pot filled with moist soilless potting or cutting mix, and put it in a protected area of your garden until the first hard frost of autumn. Once the layer is dormant and the leaves have dropped, store the pot in an unheated garage or porch. Do not water the layers until the following spring, when it should be gradually acclimatized to outdoor conditions.
Plant out in the garden in late spring or early summer and enjoy!
Plants that can be propagated by air layering include azaleas, camellias, hollies (Ilex spp.), Japanese maples (Acer palmatum), lilacs (Syringa spp.), magnolias, rhododendrons and witch hazels (Hamamelis spp.)