It is necessary to have skills and knowledge about the treatment of wounds in Bonsai as pruning leads to the creation of wounds. Here we are not talking about the cutting of thin new or green growth, but more the structural pruning leaving larger wounds in more woody growth.
It is important that the tree is healthy before big cuts are made as it is stressful for the tree and critical that the conditions are maximal for optimal healing and growth. A free draining soil, good light, water and fertiliser are all requirements for good healing.
Both cuts on roots and cuts on branches and the trunk can be treated in the same way. What you need is:
- A sharp cutter. I use a craft knife with replaceable blades. It needs to be very sharp and sterile.
- Knob cutter or concave cutter. See tissue thickness requirements in the next paragraph.
- Cut paste, either the putty type or the more liquid one.
If the tree has relatively thicker living tissue (cambium and outer layers), a concave cut needs to be made and if the tissue is very thin i.e. Azalea, then a convex cut can be made. Anything in between needs a flatter cut.
Start by using the cutters to either flatten or hollow the area of the cut wound. Use this opportunity to reduce the area by cutting at an angle or to the back of a branch.
It is important that the cut area is as smooth as possible. What is meant by this is that a ridge in the middle of a cut will cause the new tissue to bulge over that or even stop the formation of new tissue. The living tissue (cambium outer layer) must be intact and the best way to do this is to run a very sharp blade across it. This will allow intact cells to multiply better and faster to grow over the open wound. Also referred to as the cambium rolling over the wound. Once the wound is clean, relatively smooth and the cambium prepared, use cut paste to cover the wound, especially the cambium. Proper cut paste will keep the cambium moist and it also contains chemicals that will enhance the growth of new cells.
Allowing branches to elongate freely in the vicinity of the wound will help to bring nutrients and hormones to that area for faster healing.
The area could be cleaned again after a few months of healing. Remove the cut paste and study the progress. If it looks as if the cambium roll over came to a standstill, gently open the edge of the cambium up again, apply cut paste and repeat the wait and check again process.