Deciduous trees grow fast in spring. Knowing how and when to prune and trim is one of the most important bonsai skills. This post is a tutorial that should improve your knowledge of what to do when.
The first concept is one that is often overlooked in many bonsai blogs and courses – Stage of development.
Good bonsai growers do not treat all trees the same. We use different techniques and timing on young, developing trees and change as the trees become more advanced. Unfortunately many bloggers focus mainly on techniques used for older, advanced trees and seem to forget that the vast majority of the readers are relative newbies with young trees.
It is the end of September here at Shibui Bonsai and I’ve been spending quite a bit of time pinching new growth on Japanese maples.
Japanese maples have some unhelpful growth habits that can quickly spoil the look of a great tree. New shoots grow very fast. If allowed to grow unchecked they can develop very long internodes and large leaves. Excess growth can also thicken delicate twigs and cause unsightly bulges on branches and trunks. On advanced trees new shoots are pinched as soon as possible to reduce vigor and slow excessive thickening.
Usually I pinch the extending shoot tips as soon as I can get hold of them. I’ve even seen photos of growers using tweezers to get hold of the tiny shoot as early as possible.
Sometimes the shoots are already too strong and long. Don’t be frightened to nip those ones below the first leaves. There are always plenty of dormant buds at the base of any active shoot which will activate when the shoot is gone.
Pinching new shoots is time consuming on older, well ramified Japanese maples but is an important technique to maintain fine ramification and avoid unsightly thickening. Trees do not just stop growing after pinching. Some slower shoots will still be growing so I’ll usually need to pinch every day or so for a few weeks. Buds at the base of the leaves will also activate after the tips are removed and in a couple of weeks a whole new crop of shoots will begin to grow and the process happens all over again.
Younger trees that are still developing need different technique. Shoot pinching is designed to slow growth and avoid thickening. When growing younger trees for bonsai we want just the opposite so development pruning is aimed at increasing growth.
In this case new shoots are encouraged to grow. Don’t start pinching. Don’t worry about the trees looking overgrown or having large leaves. Both those things are actually contributing to faster increase in trunk thickness so let all the shoots grow when the tree is young.
In the earliest stages I often let shoots grow for a whole season and only prune after the leaves drop in autumn. That approach will give maximum trunk thickening. Unfortunately it often also produces long internodes and much of the new growth may have to be pruned off completely at some stage. fast thickening and good structure can be hard to balance.
At some stage in the development of any bonsai the grower will begin to change from this ‘growth’ technique to ‘refinement’ or ‘maintenance’. There is no set age or size when such change take place. You as grower need to decide when is right for you and for your tree. i generally base the timing on trunk development. When trunk thickness is approaching the size I want in the completed bonsai I start to change pruning technique. Change does not have to happen all at once or over the whole tree. Often I will be trimming upper branches while allowing lower shoots to grow free to help thicken those lower branches. Some shoots may be pinched while others are allowed to grow longer before pruning back. Knowing the results of different techniques can help you choose the appropriate technique and timing to deliver the result you need.
Trident maples grow in a similar way to Japanese maple but do not pose the same growing problems. Even on the mature trees I rarely pinch emerging tips really early. On trident maples I usually let the shoots grow a few sets of leaves before trimming back with scissors.