Air layering - Air layering is a method for propagating trees through the removal a large branch or section of the trunk to create a new tree. One of the main attractions to propagating bonsai material through air layering is that you can create a sizable new tree with in one growing season, as opposed to the other methods - except collecting - which all involve several seasons of development. Removing a branch from a desirable tree or bonsai requires the removal of the bark, cambium, and phloem. This prevents carbohydrates and photosynthates from flowing down the trunk, past the removal site, but still allows water and mineral nutrients to flow upward to the leaves through the xylem. The removal site should be 1" wide all the way around the branch. It must then be protected with sphagnum moss, peat moss or other water retaining media, wrapped to in dark poly or tin foil and allowed to root. When there are enough roots to sustain the branch independently (approximately between 3 to 6 months depending on species) the branch is cut off of the "parent" tree and then the new bonsai is planted in the ground or a large, deep pot.
Grafting - Grafting is a commonly used method for propagating trees, when propagation by seeds or by cuttings is impractical or impossible. Grafting techniques are often applied at nurseries for reproducing large numbers of a desirable species for use as bonsai material. The species of tree to be grafted it is called the "scion" and the tree to which it will be attached is called the "root-stock." Customarily, the "scion" is of a fine or unusual species and the "root-stock" tree is usually a common version of the same species.
Collecting - Creating a new bonsai tree by "collecting" wild plant material is certainly the most thrilling method of bonsai propagation. Finding a tree in its natural habitat that has been shaped by the forces of nature alone is tremendously exciting. It is one of those few phenomenons that defies description and must be experienced to fully appreciate. Collecting a tree from the wild is best done in early spring and with the explicit permission of the landowner. When collecting a tree it is important that you dig up a large amount of soil surrounding it, in order to avoid shocking your the tree and then immediately transplant it into your growing garden or a large, deep training box. Collected trees usually require a couple of seasons to recover, so don't attempt collecting your first tree, until you feel you are skilled enough to care for it during this extended time of rehabilitation. Collected trees hold a special place in the world of bonsai and are, by virtue of their unadulterated form, highly venerated.
Source: BonsaiBoy.com
