Air-layering is a technique in horticulture that is mainly used to propagate trees. The aim of air-layering is the vegetative (asexual) propagation of trees. The new plants forms new roots on the parent plant. After roots have formed the two plants are separated.
When air-layering 2 parallel cuts are made with a sharp knife around a suitable branch on a parent tree. These cuts must be made deep, except for the wood. The distance between the cuts is usually 2-3cm.
In the next step, the bark is removed between the 2 cuts down to the wood. Important is: The entire Phloem (vascular tissue layer between wood and bark which is responsible for the transport of sugars) must be thoroughly removed (scraped off).
Then the ring (stripe) between the 2 cuts is completely wrapped with moist sphagnum moss. A dark plastic film is wrapped around the outside of the sphagnum moss and the film is fastened tightly to the branch with a bonsai wire or string under and over the moss pack so that the moisture cannot escape.
The best time for air-layering is late spring (April). If the sphagnum moss is kept moist, new roots will develop at the upper (outer) cut in the next few months.
If the new roots are strong enough the branch can be sawn off below the roots and potted as a separate tree.
Since the air-layering is a ornate method, it is rarely used. Often to multiply rare fruit tree varieties.
Perfect roots (Amur maple)
Why does a tree form new roots
A tree has 2 different conduits systems: The Xylem (vascular tissue) in the wood and the Phloem (vascular tissue layer responsible for the transport of sugars) between the wood and the bark.
Water and minerals are transported from the roots up to the leaves in the Xylem which is located in the outer annual rings of the wood.
In the Phloem the sugar produced by photosynthesis is transported from the leaves down to the trunk or roots.
At the air-layering site the Phloem is completly severed when cutting the rings and removing all between. It is no longer possible to transport the sugar downwards. If the air-layering site is kept moist and dark the tree forms new roots at the upper (outer) cut and can transport the sugar down to the new formed roots.
As long as the roots at the air-layering site are kept moist and dark, the branch can continue to grow normally. If the roots are strong enough, the entire branch can be separated from the mother plant and potted.
Perfect roots (Spindle tree)
Why is air-layering used in bonsai styling ?
Air-layering of bonsai is used in bonsai styling as a technique to improve the quality of the trees. Sometimes a long trunk is shortened or a new prebonsai is won. A bad root basis of a bonsai or a malformation of the trunk is more often corrected by air-layering.
Shorten long trunk: Sometimes bonsai or prebonsai have a good crown, but an excessively long stem (distance between the surface of the soil and the 1st main branch is too great). By air-layering the bonsai, ie. new roots forming higher, the trunk can be shortened after removing the old roots. The proportion of the bonsai can be significantly improved and at the same time there is the possibility of making a great root basis.
A new bonsai plant can also be obtained from the branch of a normal tree by air-layering. In this way, a good prebonsai can be obtained in a few months.
Bad root basis (= Nebari): The root basis does not correspond to the quality requirements (e.g. uneven, one-sided) and should be improved. If a root basis is so bad that it cannot be improved by other techniques, air-layering of the bonsai is a way to get a completely new root basis up a little further up on the trunk. This works very well with many deciduous trees (azalea bonsai, elm bonsai, maple bonsai).
Trunk malformations: If the trunk has a malformations that cannot be corrected otherwise (for example a bulbous trunk, i.e. the trunk tapers towards the roots) bonsai air-layering can be used to create a new root basis over the malformation. After root formation and removal of the malformed trunk below the air-layering site the tree can be repotted in a bonsai pot without the blemish.
Sometimes, as with us in our bonsai nursery, the air-layering of bonsai is used on a larger scale in bonsai cultivation. From the start prebonsai with good roots can be produced in this way.
Example of correcting a bulbous trunk
How does bonsai air-layering work ?
There are various types of air-layering technology. The botanical, physiological basis is identical for all techniques.
Steps when air-layering a bonsai
- 1. Interrupt the sugar flow by cut in and remove the Phloem and the bark, by wrapping bonsai wire arround the trunk (Tourniquet methode) or by using a air-layering disc. It is important here: The Pholem must be completely interrupted.
- 2. Keeping the air-layering site moist by heaping it up with bonsai soil or packing it in Sphagnum moss + plastic foil over several months, sometimes years.
- 3. Separation of the daughter plant from the parent by cutting below the newly formed roots.
- 4. Potting the new tree. A well drained bonsai substrate is recommended here.