In teaching beginner bonsai classes we practice wiring and bending garden material and learn how, where and why branches break.
Branches tend to break where they are weakest or under the most stress:
- at the outside radius of bends
- At or near branch forks, where the wood is less pliable
- At the the site of wounds
Refering to the diagram below, one thing to keep in mind when bending branches is that the branch rarely breaks right at the point where it is supported by wire (C) or where it is compressed, even strongly (A), but rather where it is under tension but unsupported by wire (points like B) or the break illustrated.
So if you avoid trying to create bends at areas where you have wounds or forks, and wire the branch with the intention to protect the outside radius of the curve with a wire, then grasp the branch with the thumbs on the interior of the curve and push it into the wire, it will be less likely to break.
Another step you can take is to "exercise the branch" prior to wiring by bending it back and forth. This breaks up the cellular structure of the branch. Don't water the tree in the 24 hour period prior to bending. With the cells full of water (turgid) they put up more resistance to bending.
WHEN A BRANCH BREAKS
Don't try to force it back too much or you may break the cambium on the opposite side and really stuff it up. Instead try and ease it back gently. Then immobilize the branch by securing it to another branch or making a splint from a chopstick tied across the wound.
Dab the wound edges and completely seal the area with a wound sealant; you can use most anything from grafting pastes to latex sealants. The Masakuni sealant or Callusmate over at
TreeBay Bonsai Tools & Supplies
work fine. I wouldn't use cut paste for this because it's too hard to apply at a weak joint.
Hope this helps in the future.