Many bonsai artists are looking to develop their trees and in order to do this, they need to manipulate where branches are located and this can be difficult on larger thicker branches and advanced bonsai material. There are certain biological elements of the tree though that will make the bending of branches harder and one of these elements is the formation of reaction wood.
Broadleaved trees and conifers both produce reaction wood and this is wood that is formed when the wood is subjected to mechanical stress and it helps to strengthen the tree to hold the roots, trunk or branches into position. The stress may be as a result of natural forces like gravity, wind, exposure or soil movement and reaction wood is not always visible to the eye but asymmetric growth is a good indicator of this.
Nearly all branches have reaction wood as this enables the tree to hold the branches in place and conifers produce compression wood on the undersides of branches while broadleaved trees produce tension wood on the upper sides of their branches.
Therefore when it comes to moving and bending branches you need to use the various techniques in different locations on conifers to that of broadleaved trees to account for the differences in their wood properties.
Techniques used for bending branches include:
Hollowing out the branches heartwood to make the branch more flexible. This can be hard on small diameter branches and leave scars though and large wounds.
Channeling out the top side (broadleaves) or under side (Conifer) of the branch and this can cause large wounds to be created which the tree is unlikely to be able to seal over.
Splitting either along the sides depending on the movement or bend direction and again on the underside for conifers and topside for broadleaves. The split can be as little as a single scalpel blade width just to release the tension on broadleaves and compression on confers.
Notching where a small notch or wedge is removed from the branch and on Conifers this would be on the underside of the branch and on broadleaves this would be on the topside of the branch.
For more information on branch bending visit http://www.bonsai4me.co.uk/AdvTech/ATBendingThickBranchesOne.htm