Many bonsai enthusiasts derive great pleasure from growing their own bonsai trees. Some like to plant the seeds themselves and nurture them from sprouts to young trees, ready for shaping. Others prefer to take cuttings from a “parent tree” so they can grow a new tree with the parent tree’s characteristics. Still others like to grow bonsai from air layering—a technique that’s been practiced in Asia for thousands of years—or grafting, which is typically used by gardeners at bonsai nurseries. These last two propagation techniques are a bit more difficult to master than growing from seeds or cuttings, but they are reliable methods to grow your own bonsai.
Layering involves creating a new bonsai from the developed branches of fully-grown trees or shrubs. One of its advantages is that you will have a mature tree in one growing season, much faster than other methods. The principal behind layering involves intentionally injuring the tree to interrupt the flow of nutrients, or sap, from its roots to a branch. In order to survive, the injured part of the branch will first form a callus and then new buds that form roots to pull nutrients and moisture from the environment. This branch will then eventually become a new bonsai. Layering should always be done in the spring when the tree is growing and the sap is rising, no matter what the species.
There are two techniques to air-layer a tree: the tourniquet method and the ring method. With the tourniquet method, you wrap a wire tightly around the branch to partially stop the flow of sap. As the branch slowly grows, the wire will become tighter, digging into the bark and then underlying soft, green cambium layer, stopping the flow of nutrients. The branch will be forced to grow new roots just above the wire. Some bonsai experts wrap the new rooting area with sphagnum moss, peat moss, or a plastic bag to protect it. Make sure you can water the area through the wrapping. Good species for the tourniquet method include cedars, junipers, azaleas, and wisteria.
The ring method involves using a sharp knife to cut a ring around the diameter of the branch and then remove the ring of bark. Make sure you remove the bark and the cambium, leaving just the tree’s “shiny” hard wood or the tree will not grow new roots. You can dust the ring with hormone, found at bonsai specialty shops, and wrap it with moss or plastic wrap. Japanese maple, Chinese elm, and cotoneaster do well with this technique.
Your goal with either type of layering is to force the tree to send out new roots. They will be easier to see if you’ve used plastic and not moss. It’s important not to remove the branch from the parent tree too soon. Once you can see a mass of roots, or root ball—usually within three-to-six months, you can cleanly cut off the branch and place the root ball in a pot filled with peat most. Freshly potted air-layered plants should be placed in a damp, humid area and misted regularly.
Grafting is a complex method that involves combining two plants—either two parts of the same plant—or of two different plants. This is done by exposing the cambium, the layer under the bark, and joining the two parts together and allowing them to heal or graft together. The cambium of both the transplanted plant, or scion, and the rootstock or under-stock (plant which interacts with the soil) must be kept in contact with each other for several weeks for the graft to take place. The scion is usually a short piece of stem with one or two buds, and the rootstock will become the new root system. Generally, the closer in species two different plants are, the better the chances of a successful graft.