by Lew Buller
What is air layering? It is the creation of a new set of roots above the level of existing roots. By contrast, ground layering creates a new set of roots on a part of a plant that has been pinned to the ground and covered with soil.
The bottom side of the part that is being buried may be scraped or cut to stimulate growth at that point.
When should air layering be done? In San Diego, CA the best time to air layer is during the rainy season. The extra humidity in the air helps support the foliage above the cut. Tropical and subtropical trees seem to air layer best during the warm season when they begin to grow at their fastest. Other trees also seem to do well if they are air layered just before the beginning of their growing season.
Why air layer? There are at least three reasons: (1) to create a much more balanced set of roots than the plant originally had; (2) as a form of propagation, getting a jump start with a tree that can be grown and developed separately; (3) to reduce an otherwise too-tall tree down to a reasonable height for a bonsai.
Celtis sinensis –My Chinese Hackberry was grown in the ground and its roots went in all directions. They were far too large to fit into a bonsai pot. Kathy Shaner taught the class where I bought the tree and she marked the spot for air layering. This was in November and I air layered it the following spring when it was about to start leafing out. I was dubious about making the large root on the right part of the new set of roots but I did it and it worked. A year later the tree was still alive so I checked it for new roots, found them, and separated the new roots from the old when it began to show new buds, a sure sign active growth is beginning.
The cut was straight across, as close to the new roots as possible. Roots were sparse on one side and there was a gap on the other side. I knew I could balance the roots out in later transplantings so all I did was nick the cambium at the bare spot and apply rooting hormone to the fresh cut. The tree went directly into a bonsai pot.
The tree developed nicely. Within a few years, it had filled out and showed no sign of the trauma it had been through. It had the largest trunk of any tree I have air layered, nearly four inches across. Success in air layering seems to have more to do with the thickness of the cambium and the flow of sap than with size.
Ficus benjamina ‘Little Lucy’--Never throw anything away. Rather than cut the top from a ficus to create a new design, I air layer the top, propagating a new plant. The how-to-do-it comes later; right now all I am showing is air layering in process.
Removing a third branch and creating a new apex
Removing a top and leaving a side branch to become the new leader on a smaller tree
Two more planned cuts to be made after the air layer on the upper central leader is removed. That will leave me with a tree having an interesting set of curves and a substantial taper.
Quercus agrifolia (Coastal Live Oak)–A quick look at the tall, thin, sparse tree tells you that it needs to be shortened to be an attractive bonsai. An air layer is the way to make the best use of this tree. The top edge of the air layer is not a smooth cut; it has a sawtooth pattern which effectively doubles the amount of surface that can grow roots. The cut was covered with quite a bit of sphagnum moss and then wrapped with part of a plastic bag. Drainage holes were made in the bottom of the plastic and a veterinarian’s syringe was used weekly to add fresh water through the top of the plastic.
The top section was planted in a bonsai pot and thrived; the bottom section in a deep bonsai pot where it also thrived.
How to do it? A section of the bark about as long as the tree is wide is removed all the way around the tree, going down to the hard area under the cambium. All the cambium in the debarked section must be removed; otherwise the cut will bridge over and no roots will develop. On the oak, the upper edge of the cut was treated with rooting hormone, the cut area was covered liberally with wet sphagnum moss with the excess water squeezed out, the moss was tied in place with a thin strip of raffia, and then covered. The hackberry had a plastic grocery bag placed around the tree on the existing soil to keep new roots separated from old and then fresh bonsai soil was heaped up about 2 inches deep in all places. The ficus had a small plastic pot cut to fit around the trunk and then it too was covered with bonsai soil. The oak had no soil added.
When sphagnum moss-covered air layers are removed, great care must be used as the new roots are very soft and break off easily. Those air layers started in soil can be put in a growing pot immediately and enough soil added to stabilize the new tree.
I have never tried to air layer a juniper and probably never will. The very thin cambium precludes taking a ring of cambium off. Experts have recommended wrapping a wire around the trunk and tightening it very securely. New roots are supposed to come out above the ring. I prefer to start with junipers I can fix with a change in planting attitude or whose problems I can hide with an existing branch.
The last photo is an air layer I removed, only to discover it had very few roots. I put it, pot and all, into a half-gallon pot and put soil around it. If you owned this tree, how would you design it? How would you remove the small inner pot, knowing it still has a bottom?