The techniques described in Part One of this article increase the possibility of bending a thick branch, however, when a branch is so thick or brittle that it can still not be moved into a new position, it’s structure must first be weakened to make its manipulation by coiled or guy wire possible.

Part Three of the series ‘Bending Thick Branches’ addresses the techniques of ‘Hollowing’, ‘Splitting’ and ‘Channeling’.

Channeling

Hollowing and Channeling involve removal of some of the wood in the centre of the branch that needs to be bent. This can involve removing a channel of wood from along the length of the branch, or the creation a hollow so a sharp bend can be made in a small area of the branch.

The above image shows the branch of a Perovskia atriplicifolia (a rarely used species for bonsai, similar to Lavender or Rosemary). The wood of Perovskia is very brittle; this 1"/2.5cm diameter branch was too straight and was what is termed as an 'eye poker', that is, it grow straight out into the eyes of the viewer!

Before channeling, bending the branch would have been impossible without snapping it. So a deep channel or groove was carved out of the branch to make it much thinner and more pliable. As can be seen, it was then possible to wire and move the channeled branch.

Consideration must be given to the resulting scar. With this particular example, the channel in the branch will not heal over and will always be visible. However, the tree features many shari and jin already and so the channel can be said to complement the overall design. An alternative would of course have been to make the channel underneath the branch so it could not be seen from at least the front view.

 

Hollowing

The first branch of this Hawthorn required some movement to be added to break up the long, straight section and to bring down the tip of the branch. As a short abrupt bend was required and a long wound (caused by Channeling) needed to be avoided, the branch was hollowed.

(Seen from the reverse side) To hide the resulting wound, the hollow was made at the back of the branch using a Dremel with a small router bit. As much as possible of the interior wood was removed without damaging the cambium layer.

Having finished the hollowing, the branch was easily bent downwards using two guy wires to position the branch precisely.

(Seen from the front view) After the branch had been positioned, the hollow was filled with sphagnum moss and bound tightly with black plastic tape. This will help insulate the wound through the Winter.

Update Spring 2009

2 years later and the branch has healed well. All that remains of the hollow is a natural looking uro on the inside bend of the branch. The guy wires are still in place and I will keep them in position for another few months just to ensure that the branch does not return to its original position at all. With fast-healing tree species that callus quicker than Hawthorn, the guy wires could easily have been removed last Summer.

This image shows the first branch from the opposite angle (from the front of the bonsai) and compares it to the original position before the bending technique was carried out.

Splitting

I have seen thick branches split in half along their length, bent into position and then the two halves 'pushed' back together. This creates a laminate effect making the two halves of the branch more pliable. Although the two halves would often callus together, in all honesty, I did not find the resulting effect pleasing to the eye. There is a great tendency for the branch (or trunk) to develop inverse taper in the areas that have calloused and joined together.

Virtual rendition of the Hawthorn branch, split and ready to be bent. The branch can be split with either a fine wood saw or branch splitters. In this case, the resulting scar would not be pleasing given the surrounding smooth bark of the branch.

Splitting does have its place in bonsai however. It is best used when there is a need to bend a live portion of trunk or branch away from a section of deadwood. Using a saw or branch splitters, the live wood is literally split away from the deadwood. Or, the deadwood can be removed entirely from the live wood (similar in principle to channeling) in order that the live wood can be bent.

Virtual Images of a Juniper in development: from left to right. The first section of the trunk cannot be bent as it is too thick. So the live wood is split from the deadwood. The live part of the trunk is now thinner and can be bent using coiled wire and guy wires.

The upper branch of this Hawthorn bonsai was not only very straight but too thick for its position in the apex of the tree. So I split it along its length. This allowed me to add interest to the branch by bending it with coiled wire and also 'thinned' the diameter of the branch so it was a more appropriate diameter.

Further notes

As with some of the other techniques described in this series of articles, hollowing, channeling and splitting all carry the real risk of causing the death of a limb or even the tree itself if not carried out correctly and the correct aftercare provided. These techniques should be considered as advanced and only carried out on healthy, vigorous trees and limbs that are able to respond to such invasive work.

Protect wounds by your usual method, be it wound sealant or otherwise (there is debate currently as to the necessity of some or even all wound sealants). Personally I find a smear of vaseline/petroleum jelly more than adequate to protect the exposed cambium.

When hollowing or channeling, remove enough wood from the branch to enable bending without splitting or otherwise damaging the outer bark/cambium layer, but leave enough wood to ensure that the branch has enough strength to support its own weight. Keep checking the flexibility of the branch as you remove the wood.

When removing wood from the centre of the branch, if you see the green of the cambium, you have drilled too far. Seal the cambium and continue to remove wood elsewhere!

As with other techniques described in this series, the best time to carry out this work is in late Summer or early Autumn when the heat of the Summer has passed and there is plenty of time for the wounds to start healing before the onset of frosts. Do carry out this work while the tree is active (in leaf) so that its response can be gauged immediately and so that the tree can respond to the work (by healing) immediately.

Be cautious; if in doubt, create the channel or hollow or split the branch, allow the wound to heal and then carrying out the bending and wiring, weeks or months later.

Finally, make sure these techniques are actually necessary. Always bend a branch using coiled wire, guy wires or other less intrusive techniques, if at all possible.