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.

This second article addresses the technique of notching

The Basic Principle of Weakening Branches in Order to Bend Them

As with a tree trunk, tree branches consist of a live layer of living tissue (immediately below the bark) that surrounds a ‘dead’ wooden core. The core of a branch (or trunk) exists to provide the branch strength and structure.
This structure supports the live tissues, holding the foliage in position and is strong enough to support the branch so that it doesn't collapse under its own weight, even when snow laden or buffeted by winds.
It is this inner core of dead cells or wood that we are trying to work against when bending a branch. It is also this ‘deadwood’ that we can weaken or remove in order to bend the surrounding living tissues and therefore, the branch.

There are a number of techniques for weakening a branches’ structure so it can be bent; all should be considered ‘advanced’ and only used with great care and experience. All should be considered risky techniques that can lead to the demise of the branch if care is not taken.

‘Notching’, ‘Hollowing’, ‘Splitting’ and ‘Channeling’ must only be carried out on healthy trees and vigorous branches that are strong enough to heal and recover from major trauma. The one major downside with these techniques is that they often produce large wounds that may not ever heal over; such wounds should be made so that they are out of sight of the front of the tree and ‘dressed’ if possible to be made to look like natural deadwood features such as a ‘uro’ (hollows) or ‘shari’ (lengths of natural deadwood often seen on coniferous species such as Pine and Juniper).

Timing

The techniques described in parts two and three of this article all cause major trauma to the branch that is to be bent.

The concept held by some enthusiasts that carrying out major work on a tree during the Winter when it is dormant or 'asleep', almost in an effort to 'fool' the tree, is wrong and a little misguided.

If carried out in the early-mid winter when the tree is dormant, the damaged area will not heal until the tree has returned to active growth, weeks or months later. This will leave the wound(s) exposed to frost and further trauma for too long a period.
For this reason, these techniques should always be carried out during the growing season while the tree is in active growth and the threat of frost damage can be kept to a minimum.

For the majority of tree species, the best timing is from midsummer to late-summer or very early Autumn when the first frosts are not due for at least 6 weeks.

By midsummer, a tree will have extended the new leaves and shoots of the growing season and will be at it’s strongest and most vigorous. Work carried out from mid to late Summer will allow the tree to heal quickest, reducing the risk of dieback or infection in the tree without interrupting growth.

For resinous coniferous species such as Pine or Spruce, work should be carried out in late Summer when sap flow is reduced. For deciduous species that have a tendency to bleed, these techniques should be avoided during early Spring before leaf break or bud extension.

Above all else, always try bend a branch with coiled wire and/or guy wires before using these techniques.

Notching

Notching is simply a technique where the branch is cut across its width and the branch is then bent into position.
It is a very quick and straightforward technique to carry out however it has a tendency to produce some callus swelling in the area of the notch.
This technique is also more suited to deciduous and broadleaf species that do not have as strict ‘life-lines’ as conifers (if a life-line supporting a secondary branch and/or foliage is entirely severed on a coniferous species, the live growth can and will dieback).

Branches must be wired or at least guy wired to hold the limb in place while the notch wounds heal and callus. Smear a coat of Vaseline around the exposed cambium of coniferous species or use cut paste on deciduous species.

Two angled cuts are made approx 2/3 of the way through the limb to be bent. If the cuts are not made deep enough, the branch will not bend neatly and cleanly, if at all. The notch is made using a thin saw and should form a triangular shape so that when bent, the two sides of the notch meet; as the resulting wounds callus over, they ‘graft’/grow together.

This image shows the cascading branch of a Hawthorn that has been notched and has since healed over. It also shows one of the disadvantages of notching midway along the length of a branch; the resulting callus formation can create a bulge in the branch. For this reason, a notch made in the middle of a branch should be placed, where possible, so that the notch itself and the resulting wound are invisible from the front of the tree.

Notching is useful for altering the angle at which a branch leaves the trunk of a tree. This can often be difficult to change with just wire alone.

The base of the branch can be notched at the bottom and can then be pulled downwards with coiled wire or guy wires. The sides of the notch are pulled together and they will eventually heal together.

Some enthusiasts prefer to notch above the base of the branch, rather than below. This leaves the notch open and visible until the notch calluses over and fills out the gap.

Ultimately. either method works reasonably well and should probably be used according the attributes of the plant species it is applied to; some species are slow to form sufficient callus to fill in the notch and a bottom notch is preferable.

Notching can also be useful for bending thick roots. There are occasions where a bonsai will not fit into its intended bonsai pot because of a thick lateral root. If removal of the thick root may threaten the health of the tree, it can be partially severed with a notch instead and bent so that it then fits inside the pot.

The notched area will often callus and produce new roots during the course of a growing season. The thick root can then be pruned back to these new feeder roots at the next repotting. This allows a tree to be fitted inside an otherwise appropriate-size pot and also allows the tree to slowly adjust to the removal of a major root.

Notching Examples

These images show the repositioning of a short and brittle Acer palmatum branch by notching at its base; the first image was taken in March 2006, the second in November 2006. The notch was made in late June at the base of the branch so that it was hidden from the front of the tree. A guy wire tourniquet was used to hold the branch into position.

The healed notch can be seen from the left hand side of the tree.

 

The thicker of the two trunks in the foreground of this Elm clump leans backwards too far and is growing at a poor angle compared to the other 4 trunks in the clump. The trunk is too thick to manipulate by coiled or guy wire alone so the notching technique is used to rearrange the angle that it grows from the base.

The image on the left shows the trunk just after starting work on the notch; the image on the right shows the trunk after the notch has been completed and the trunk pulled into an upright position with the help of a thick copper guy wire. This work was carried out during the Summer of 2005; by the Spring of 2006 the guy wire was removed and the trunk remains in its new position to this day.

In this final image, the size and depth of the notch in the base of the trunk can be seen.

 

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