Updated: Jan 7
Bending Large Bonsai Trunks Can Be Difficult, But Can It Be Done?
Today we are going to be looking at a Technique called the wedge cut that is used on larger Black Pine and Ficus Trunks. For now i am going to limit this technique to those species as so far these are the only 2 i know for sure that can handle this well. In simple terms a wedge cut is taking a chuck of the trunk out that is in the shape of a slice of pizza. This create a space for the trunk to be able to bend with far less stress and pressure on the trunk. If you think about a trunk that is being bent any material that is on the inside of the curve is being compressed as the bend is applied, the outside curve of the bend is being stretched which can cause the bark to tear open. If we remove the material from the inside of the curve then we can take away the pressure that is caused by the wood that is being compressed and avoid tearing on the outside of the curve but this also makes it actually physically possible to bend the trunk ( with some help from guy wires and some times a Bonsai Jack ).
In Autumn i undertook this procedure on a Black Pine that we had as nursery stock for sale here at Bonsai-En. Unfortunately the tree never sold as it had a long thick straight section in the tree and to the untrained eye seemed like material that couldn't be utilised as Bonsai. After seeing this tree sit there for so long i decided to rectify the issue and turn the tree into a Cascade Black Pine. To get the cascade i had to lay the tree on its side and perform a wedge cut on the straight section in the trunk to be able to get it to drop down and cascade.
I will show some photos here of that process then i will explain some things to understand about the technique.
As you can see in the Above photo the tree had a thick straight section half way up the trunk.
In the above photo the tree is secured to the work bench with a ratchet strap to ensure the tree does not move while being cut as the cut needs to be very clean and precise to ensure fast healing. The bending will also take a lot of muscle so its important that the tree is sturdy.
In the above photo you can see where the wedge cut was removed from the trunk ready for bending to begin. The material that was removed is what would have been compressed if i didn't remove the wedge.
In the above photo you can see the result of the bend which is being held by a thick guy wire and some thick wire. The wire is not really helping the bend but was to help support the outside of the bend.
in the above photos you can see the piece that was removed and the wedge cavity closed up. After this photo was taken cut putty was applied over the area to aid with quick healing.
It has now been 3 months since this was performed and all branches past the cut are still growing and living giving me a successful wedge cut. But what gave me the confidence to ensure success with this technique? Let have a look.
First of all timing is everything, like everything in Bonsai if the technique is performed at the wrong time you are going to get questionable results even if your practical hands on technique is sharp. This technique should be performed in the autumn period as this is the time of vascular growth in our trees, In the growing season we have vegetative growth which requires resources to be moved around in the tree at a rapid rate, If you were to perform a cut that large through the growing season you are going to end up with a lot of sap bleed out on the tree which will cause it to weaken significantly. Doing this technique during the trees vegetative growth period in autumn see's minimal bleed out and a quicker response to the cut due to the nature of vascular growth.
Another thing to keep in mind is your cap for this cut is 60% of the way through the trunk. do not cut anymore than 60% of the way through the trunk, i would start testing the bend at around 50% and see how far you get, then as you need more slowly proceed with the cut until you reach 60%. We still need to keep a good amount of live tissue behind the cut to allow the top of the tree to get nutrients and resources. If you cut off that supply chain this could be a point of failure.
Make sure you use a clean sharp saw that has a very precise cutting edge, this technique is not for cheap tools. The cleaner and straighter the cut is the better chance of wound closure. Although this wound will never completely close the closer you can get the 2 surfaces together the cleaner the cut will look.
When bending make sure that you still keep an eye on the outside of the bend for tearing, you can get away with some minor tearing but if it really starts to tear open then hold off on bending any further, this is why its also a good idea to only take 50% to begin with then slowly take little bit by little bit until you have the desired bend and there is minimal tearing and no more then 60% or material taken from the diameter of the trunk.
Apply cut putty or cut paste to the wound when complete to help protect it through the winter season that wont be far away after this technique is performed. you want to make sure you stop any moisture from getting inside the wound and rotting away over winter. With an open wound that large you also open yourself up to fungal infections which are much more liley during winter.
I hope this has shown you what can be done on the more extreme end of Bonsai. Most people think of Bonsai as very delicate trees but with the right timing and technique you can get away with some pretty intense work.
Until Next Time, Enjoy Your Bonsai Journey.