Article written by Gary English and published on this website with kind permission of The Gardener magazine.
© Gary English gary@cybersmith.co.za
© The Gardener Magazine - Editor: Tanya Visser tanya@thegardener.co.za
Trunk Cutting
I recently received the following question via email from Philip Rubin. It covers an important aspect of bonsai so I thought everybody would benefit from the answer.
"Hi Gary
I am fairly new to Bonsai but I have a quick question.
If I have a tree such as a Juniper or an Acacia from a nursery, and the tree is somewhat bigger (taller) than a regular Bonsai, say half a metre in height, can I simply lop off the top third or so, even if there are almost no branches below?
Will new branches grow?"
Hi Philip,
You question is actually a very good one. When bonsai enthusiasts buy a plant from a nursery, most of the time the first thing they do is to cut the trunk off fairly close to the ground. If this is done in the presence of the nursery owner they seem to go into some kind of epileptic fit.
Mostly trees are bought because of the shape of the trunk and the root structure. The rest of the tree is often removed (cut at about 45 degree angle) and the cut sealed with tree sealer or wood glue. The tree will then sprout a whole lot of smaller shoots at the cut. You must then decide which shoots to remove and which ones to keep. One of the most basic bonsai principles is that the trunk is for ever, the foliage gets renewed every season, consequently the shape of the trunk is possibly the most important aspect of a bonsai tree.
Be warned though, some trees, like the Acacia, do not recover very easily from this fairly major surgery. This is because acacia generally have quite weak roots. Acacia are also prone to something called “die back”, which simply means that if a branch is cut, the remaining stump will shrivel up and die back to the closest node or shooting point. If it is cut too close to the node then the die back may affect the branch past the node which could be disastrous. Always leave a fairly substantial stump when cutting Acacia.
“Buds easily on old wood” is a term that tree books use to describe the ability of a tree to generate new shoots on the trunk and thicker branches. Species that bud easily are very desirable for bonsai.
Only do surgery on very healthy trees, and in the case of chopping the whole trunk off, do this towards the end of winter when the sap flow is slow but about to speed up for spring.
Watch out for major cuts on Junipers. They are evergreen trees and they need a fair amount of foliage to grow, unlike deciduous trees which live off nutrients that have been stored in the trunk and branches. If you remove all or most of the foliage from a juniper or pine it will die. In this case it is best to cut back sections at a time. This will reduce the trauma.
One quite important trick is that once you have removed a lot (or all) of the foliage of a tree, you must then place the tree in a dark shady place for at least two weeks and keep the soil moist. The reduced light will stimulate the tree to put out the new shoots. Also, turn the tree every few days so that each side of the trunk gets a similar amount of light.
Lastly, a word about proportion. The height of the remaining trunk is actually quite critical. Your decision of where to cut the trunk must be made with the final style and design of the tree in mind. The above technique creates very nice baobab and flattop styles, but also with a bit of work one can still achieve the other styles like the informal upright. I will write an article on the basic proportions of bonsai trees in the near future.