One method of growing bonsai trees is the air layering propagation technique. This technique has been around for over 1,000 years. This form of propagation is readily observed in nature, where we see new trees born from branches that have sprung their own roots.
This method of growing bonsai is not as popular in the West. It is however a great way of cultivating and growing bonsai. Bonsai trees grown using air layering technique matures much more quickly - in about 2 years. With this technique, you can actually choose the branch for your new bonsai and select one that has your preferred shape, form and character.
The Basic Principles of Air Layering Propagation
What makes the air layering propagation method viable is the propensity of the branch to survive in conditions of scarcity. In air layering, the flow of sap and nutrients to the branch that you want is cut. When this happens, the tree will try to restore the flow by bridging the cut. If this is impossible, the branch will strive to survive by sending out roots.
There are 2 basic methods of creating this injury. One method involves cutting a ring around the location where you want the root to grow. To do this, use a sharp knife to create a ring around the circumference of the branch. The ring should be at least twice the diameter of the branch to prevent the tree from bridging the wound. Remove the bark and the underlying soft layer, until you see only wood.
The other method of creating the injury is the wire method. In this technique, a wire is used to create a tourniquet around the proposed site for the roots. As the branch grows and thickens, the wire bites into the bark, slowly interrupting the flow of nutrients. This technique is suitable to trees that will not survive the complete removal of the bark.
How to Ensure Successful Air Layering Propagation of Bonsai
The best time to start the air layering process is during early spring. Starting this early will give you the most amount of time to establish strong roots that will allow you to transplant the branch to a pot well before winter.
That being said, specific trees can be started on this method at different times of the year to achieve good results. Air layering of deciduous trees are best done in spring, from April to May. For evergreens, air layering is best allowed to start a little later, from April to July. Timing the air layering at the point at which the trees are experiencing vigorous growth is a great way to ensure rapid rood growth on the air layered branch.
A branch that is at least 2 inches in diameter is a good candidate for air layering. Choosing a site just below nodes is another way of ensuring the survival of the tree. This is because you are giving the new tree a lot of opportunities for new growth.
Keep in mind that certain tree varieties take well to certain methods of air layering and may not tolerate the effects of other methods. Research this well to make sure you apply the correct method.
Once the proposed site has been injured, put rooting hormone on the site and then wrap it tightly with wet long-stranded sphagnum moss. Wrap the moss in clear plastic bag to keep it in place. This serves to insulate the area and create a condition that supports vigorous root growth. Put a small hole on top of the bag to allow watering. The sphagnum moss should be kept damp the entire time.
Depending on the tree variety, roots can be observed growing inside the bag anywhere between 3 weeks to 3 months. Do not remove the moss covering bag. Just allow the roots to grow until they become mature and turn brown in color. Once this happens, you should be able to safely cut the branch and plant it in a pot.
When the roots are ready, here’s how you transfer it to its new environment. Cut as much of the branch that you can below the root ball. Remove the plastic bag, but keep the sphagnum moss in place. Handle the root ball very carefully. Remember that at this stage, the root is still brittle and very easily damaged.
Choose a location that is shaded and protected from the elements. Plant the root ball in a pot of sphagnum moss. Secure the branch by tying it with strings. You want to keep it in place and resist the effects of strong winds. Mist it regularly to keep the soil damp and moist.
When separating branches, be sure to do so at least 6 weeks before winter hits. This will allow the roots to establish themselves well before winter arrives. If you think the air layer is not yet ready to be transplanted and it is almost winter, the best thing to do is to leave the air layer attached to the parent tree. This will give it the best chance to survive. You can then choose to separate it in Spring.
Once the new branch has established itself, or even while attached to the parent tree, it typically will not require any special care during winter. The sphagnum moss and the plastic bag serves to insulate the roots and protect it from winter frost. For severe winters or for added protection, you can wrap a layer of plastic, bubble wrap or fleece around the new roots to further insulate it and keep it from damage. Roots that die during winter are often replaced in spring.