Air Layering as a Source of Bonsai by Norman Haddrick Air Layering is a method of propagation believed to have originated over 1,000 years ago, in China. The many variations of air layering techniques can be applied to various tree species, whether hardwood or softwood, slow growing or fast growing types, to obtain the best possible results. To understand why and how air layering works, you need to understand the basic cellular structure of a tree and its functions. Diagram 1 below shows the 5 concentric layers of tree cells, called annular rings. 1) Heartwood is comprised of old, dead cells which act as a central support system. 2) Sapwood cells are living cells, which take up water and dissolved minerals from the soil via the root system, up to the leaves. These cells are also called Xylem cells and they are a part of the tree¹s transport system. 3) Cambium cells are the trees only productive cells. They are responsible for the growth, renewal and healing of the tree¹s structure. 4) Phloem cells are live cells located on the outer side of the cambium cell layer. They form the soft inner bark layer which transports sugars produced in the leaves, down to all parts of the tree, to be stored in the phloem cells as starches for use by the tree to sustain good health. 5) Bark is formed by dead phloem cells, which create a protective outer layer around the structure of the tree. Roots: Widespread surface roots provide a strong base. In the extremities of the fine, fibrous feeder roots of trees there are root tips, which seek out water with dissolved nutriments in the soil, and transport these elements up through the sapwood, to the leaves. Leaves/foliage: The leaves use these elements to manufacture sugars by taking hydrogen from the water, combining it with carbon, from carbon dioxide in the air, and with solar energy, photosynthesis transforms these elements into sugars and starches for the tree¹s use. Photosynthesis is light energy (photo), which is used in building complex substances from simple substances (synthesis), and the product is glucose. The by-product is Oxygen. This process only occurs in organisms that contain chlorophyll. Air Layering - The Method: If you have access to an unusual branch of a suitable shrub or tree species, from which you wish to create a future bonsai, consider trying the following air layering methods in springtime or early summer: Sketch 2A shows a suitable branch, below which two circular cuts have been made with a sharp knife, through the outer Bark, the Phloem and Cambium. All of these layers are removed, down to the Sapwood. If the cambium is not removed completely, or if the ring-barked section is not wide enough, (i.e. 1 to 1.5 X the branch diameter), the section may heal over without producing roots. Apply a root stimulant to the top of the ring cut, 2B, and then surround the ringed section with damp sphagnum or peat moss. Firmly encase the ball of damp moss in clear polyethylene plastic and secure it, top and bottom, 2C. Surround the clear plastic ball with a separate layer of black plastic and secure it also, top and bottom. The black plastic will retain warmth in the moss ball to stimulate root growth, while restricting sunlight, which may kill exposed, delicate new root tips. This method works very well on fast growing species, and produces roots evenly around the cut, 2D. Periodically, check the moss for moisture level and root development by loosening the top of the black plastic cover to look through the clear plastic. Now, consider the tree functions, described above. In making this cut, we have not affected the transfer of moisture up from the roots, through the sapwood to the foliage above the cut. The leaves on our future bonsai go through their processes, transpiring excess moisture and Oxygen, producing and sending the starches and glucose down through the phloem cells to be stored or used, as required. When this downward flow reaches the top of the ringed section, it has nowhere to go and begins to accumulate at the cut. The cambium layer has already started to produce new cells, and the resulting callus could eventually repair the damage at the cut section. However, we have provided a medium, which is a warm, moist, and dark environment in the presence of a rooting hormone, growth stimulant, and so the cambium creates new roots from the callus into the moss. (I have had best successes when dampening the moss in water treated with a few drops of Superthrive). When the moss ball is filled with enough new roots to sustain the tree, cut it from the parent tree. There are many cut variations, which can be used to ring a branch, intended for either speeding root production of slow growing species, such as pines, or, for the creation of a better root buttress on many species. An excellent, illustrated reference on this subject is Deborah Koreshoff¹s book, ²Bonsai, Its Art, Science, History and Philosophy², pages 29 to 32..