How to create a good Bonsai trunk
The base and trunk is what immediately attracts attention when looking at a Bonsai tree. We discuss the most important aspects of the trunk: the surface roots, tapering, thickness, and shape.
The Nebari (surface roots, or root-flare) is important in providing a Bonsai with a well-balanced appearance. Deciduous Bonsai, like the Japanese maple, can often be found with wide, radial surface roots, that anchor the tree. More information can be found at the Surface roots page.
A trunk should be thicker at its base than at the top of the tree; this is called tapering. Although it is hard to improve irregularities in the thickness of a trunk (select trees well before buying them) it is possible to achieve minor changes:
Bonsai plants often look older than they are when they have a thick and gnarly trunk. The only way for a trunk to grow thicker is to let the tree grow freely in a large container, without pruning it for several years. Once you are satisfied with the thickness of the trunk you can train it again and place it in a smaller pot.
One technique to thicken a trunk is to grow "sacrifice branches" from the trunk. These branches are not pruned at all for two to five years, thickening the trunk as they grow quickly. After the two to five years the branches are removed.
The overall shape of a trunk is one of the most eye-catching aspects of a tree. Some Bonsai have slender, elegant and twisting trunks; Juniper Bonsai for example often show these qualities. The classic Japanese black pine on the other hand often reveals a thick, heavy trunk. As it is nearly impossible to bend a trunk once it reaches a certain thickness (until that point you can use a trunk-bender) it is important to take the shape of the trunk into account when buying it.