Nebari for bonsai is Japanese for surface roots. In the overall appreciation of a bonsai tree, surface roots are essential to create the illusion of a strong and aged tree. An idea root system for a bonsai tree would be a radial root system; a system that would be dispersed around the trunk evenly. The root base should have even roots all around and be of a width and extent of at least twice the diameter of the trunk of the bonsai tree. This will create an harmony and balance in between, roots, trunk, branches and foliage.
While a nebari is essential for the aesthetic of the bonsai tree showcase, it is also another an important factor in stabilising and anchoring the bonsai tree in itís bonsai pot.
When a bonsai tree doesnít have the proper root system to be successfully displayed, the root system can be corrected with a few grafting techniques. The most common are the root grafting made with seedlings carefully placed at the root base of the parent tree. The seedlings are taped around the trunk and as both will grow, the bark will fuse together. When both the parent and seedling have carefully fused together, the top of the seedling can be removed, leaving the roots of the seedlings attached to the parent bonsai tree.
Similar technique can be done with a phoenix graft. The difference is that a hole is pierced across the trunk of the parent bonsai tree. The hole pierced will be a few millimetres bigger in diameter then the seedling used in the graft. Then, the seedling is passed in the hole. As the seedling grows bigger, the bark will fuse with the parent plant. On the other side of the trunk of the needed roots graft, after the seedling as fused, you can cut the top part of the seedling leaving the roots attached to the bonsai tree.
With both techniques, the roots newly grafted will grow bigger and will then replace the missing roots in the incomplete root system, see nebari.
Another technique would be a ground layering. This technique is needed when the nebari, or surface root system is not incomplete but inexistent. The technique is simple and is copied from an airlayering technique. It is the tourniquet technique. About an inch over the beginning of the deficient root system, you would wrap a wire around the trunk and put this trunk in the soil with soil level over the tourniquet. After two years in the soil, new roots will have developed just over the wire. These roots are developed by the tree in order to continue its development. As the trunk gets bigger, the trunk is choked by the wire cutting down the flow of sap. To palliate this lack of sap, the tree will develop new roots at the beginning of the area where it is not restricted.
Forced Lateral roots
It is important to start an early age the development of the surface roots. A technique that can be successful with seedlings is the removal of the tap root after the seedling as produce its for set of true leaves. Replanting the seedling without the tap root will force him to reproduce lateral roots. The next year, when repotting the young seedling, newly created lateral roots should be combed and carefully place laterally to further develop the future surface roots. Same process can be accomplished with cuttings.
Nothing better then nature
While this last method is a good method, nothing beats a natural root system. With seedlings, it is possible to realise this. All you need is a seedling, the sun and lots of space. Field grown seedlings will develop a natural nebari as long as they are provided enough light/sun and space to grow their roots. A plant grown with sufficient light will not grow elongated and the branch system and internodes will be shorter and more compact. The branch system is the replica of the root system of a tree. A healthy root system will produce great branch structure and vice versa.