This is a very good way of starting a tree. The technique of layering can be split into two types.

Ground layering

Air layering

If a tree is being Air layered, the top part will be grown into a new tree, the bottom part will produce shoots, one of which will be used to create a leader that will eventually give a good tapered trunk.

The layering is wrapped in clear plastic, and then closed up with black plastic, as roots grow best in the dark.
The black plastic can be opened when you wish to inspect progress, or check that the moss is still damp.
With both ground, and air layering, the technique below should be followed, noting the difference between deciduous and coniferous trees.

• First remove a ring of bark, about as deep as the tree is wide.
• Smear the upper cut with hormone rooting compound, and wrap in wet Sphagnum moss. (Not needed in ground layering).
• Enclose in a plastic bag, and tie both ends. (Not needed in ground layering).
• Check regularly for root growth, and that the moss is still damp. (Not needed in ground layering).
• Allow time for enough roots to develop to support the tree.
• Cut tree from stock tree.
• Pot tree into a container. * But do not remove moss.
• Tie the tree into the container to stop it moving around, moving around in the pot will break the new roots, and kill the tree.

Note: In most cases you are advised to leave the layering until the plant is in growth the following year.

When can you air-layer Bonsai?
Layering should always be done during the spring, when the tree already started growing after its winter rest.

The 'Ringing' method works well with deciduous species; however for conifers an alternative way is best. This involves wrapping a piece of strong wire around the trunk, and twisting it until it bites right into the bark. Then cut a number of small nicks in the bark just above the wire, and apply hormone compound, then wrap in moss.

Conifers take longer to root by layering, and may not show roots until the following year.

On the whole most species will root but pines are more difficult, and may take up to five years to do so. Air layering should be your preferred option as it produces a good radial root formation.

The moss in the bag must be kept moist at all times. There is a tendency for the water in the moss to be absorbed into the trunk, and out through the leaves. You may have to open the top of the bag, and pour water into it.

When it's time to separate your tree, try to create a balance between the volume of root, and the amount of foliage present. This may mean reducing the foliage, but a tree that is 'out of balance' like the one on the left may find it difficult to survive.

Under no circumstances should you try to remove the moss, as this will damage the soft new roots. The moss will decompose in a short while, and any left can be removed when the tree is next repotted.

Acknowledgment to Bonsai Primer.com

Bonsai, Layering, Air layering, Ground layering