Air layering, also known as marcottage, is a method of vegetative propagation used to create a new, independent plant from a chosen branch while it is still attached to the parent tree. This technique involves inducing the branch to grow roots by wounding it and surrounding the wound with a moist rooting medium. Establishing a root system on the branch before separation bypasses the difficulties often encountered when rooting conventional cuttings. This process is particularly useful for fruit trees because the resulting plant is a genetic clone of the mother tree, preserving desirable traits like fruit quality and disease resistance. This method allows growers to quickly produce a larger, more mature plant than starting from seed.
The Biological Mechanism of Air Layering
The success of air layering relies on manipulating the plant’s vascular system, specifically the phloem and xylem tissues. Photosynthesis produces carbohydrates and hormones, which are transported down the branch through the phloem layer to fuel growth. When a ring of bark is removed from the branch—a process called girdling—the downward flow through the phloem is interrupted, but the upward flow of water and nutrients through the xylem remains intact.
This interruption causes an accumulation of sugars and growth hormones, particularly auxins, just above the wounded area. Auxins are plant hormones that initiate root development. The high concentration of these compounds, combined with the humid environment provided by the rooting medium, stimulates undifferentiated cells near the wound to develop into adventitious roots. The removal of the vascular cambium layer is necessary to prevent the plant from quickly healing the wound and restoring phloem continuity.
Step-by-Step Guide to Creating a Fruit Tree Layer
The air layering process begins with selecting a healthy branch, typically one to two years old and about the thickness of a pencil or slightly larger. The ideal time for this procedure is spring or early summer when the tree is actively growing, which makes the bark easier to remove. Necessary materials include a sharp knife, rooting hormone powder, moist sphagnum moss, and a protective wrapping material like plastic film or aluminum foil.
The primary technique is girdling, which involves making two parallel cuts around the circumference of the branch, spaced about one to one-and-a-half inches apart. After connecting these parallel cuts with a vertical incision, the ring of bark and the underlying phloem layer are peeled away completely. It is important to scrape the exposed inner woody tissue to remove the slick, green cambium layer, ensuring no vascular tissue bridges remain that could allow the wound to heal.
Once the cambium is clean, rooting hormone powder is applied directly to the exposed cut surface just above the girdle to encourage root development. Next, the rooting medium, typically sphagnum moss soaked in water and squeezed until damp, is applied around the wound. The moss should be moist like a sponge, as excessive wetness can lead to decay.
The moss-wrapped wound must then be securely covered with a sheet of plastic film, sealed tightly at the top and bottom with electrical tape or twist ties to lock in moisture. This plastic covering creates the humid microclimate necessary for root formation and prevents the moss from drying out. Covering the plastic with aluminum foil is recommended, as it blocks light and inhibits algae growth.
Advantages for Fruit Trees and Post-Separation Care
Air layering offers several distinct advantages for fruit tree propagation. The most significant is the creation of an exact genetic replica of the parent plant. Because the new plant is a clone, it inherits all the desirable characteristics, such as fruit size, flavor, and maturity rate, ensuring the new tree produces the same quality fruit as the source tree. This method is especially useful for woody species and tropical fruit trees like lychee, guava, citrus, and figs, which are often difficult to propagate from simple cuttings.
Another benefit is the ability to produce a larger, more established plant in a shorter time compared to growing from seed, leading to earlier fruit bearing. The process typically takes 8 to 12 weeks. Once a robust network of white roots is clearly visible through the plastic, the new plant is ready to be severed from the parent tree with a clean cut made just below the root ball.
Following separation, the plastic wrap and moss are carefully removed, and the new tree is immediately potted into a container with well-draining soil. Newly potted air layers are highly susceptible to transplant shock because the small root system cannot yet supply enough water to the established leaves. To mitigate this, the young plant should be placed in a lightly shaded area and kept humid for several weeks to allow the roots to establish and acclimate to the soil environment. Delaying fertilization for two to three weeks is also advised, giving the plant time to recover before being introduced to concentrated nutrients.