Pruning Bonsai Maple Trees

Introduction

The aesthetic and monetary value of a Bonsai tree is determined by its health, shape, size, age and these days the celebrity status of the artist. All of these, accept for the last one, can be enhanced through proper care which includes shaping, pruning and pinching as developmental techniques.

Why Pruning

There are a few reasons why Maples should be pruned or trimmed. Developing structure is a big part of this and then culminates in developing good ramification and a pleasing shape. The different phases depends on whether you are working on a seedling, a well-established tree or a tree that was field grown and in its early stages of development.

The seedling or young plant is the easiest as it can still be bend in a suitable shape and very little cutting is needed until later. Use wire for this bending. At this young stage it is important to develop the basic structure and to leave as much growth as possible to feed the trunk.

The more advanced tree will have its main flow established and the emphasis is now on branch development according to the desired style and shape. The great thing about Maples is that you can cut a whole branch off and in a few years’ time you can grow a new branch in a more suitable place or with more movement in it. This is where patience comes in.

This is also the time to remove unwanted growth such as bar branches, crossing branches, branches that do not add to the aesthetics of the tree like branches growing upwards and downwards, interfering with layers above or below it.

Once the tree is established and with a desirable structure and flow, you start to refine the secondary and tertiary branches by either trimming back to a couple of leaves or by using the pinching method. This enhances ramification and forcing the internodes to be shorter. Defoliation is part of this strategy and this also helps to reduce the leave size.

I also do believe that deciduous trees, like conifers need to have the energy throughout the tree balanced. Apical dominance plays a big part here. Sometimes lower branches become weaker. This can be due to the top of the tree growing too vigorously or just because the lower branches are shaded out by the upper branches. By removing some of the upper leaves or just reducing them in size by removing about half of the leave, more light is let through.

The Timing of Pruning

The best time for structural pruning and shaping is early to late spring as the tree is getting out of dormancy and will be full of vigour to get growing again. Heavy pruning or shaping should not be done around repotting time when large quantities of roots are removed. A lot of the trees energy is stored in the roots and when this is removed, new growth will be jeopardised. If you are not going to remove a lot of roots during repotting, pruning can be done at least two weeks before repotting.

How to Prune

For structural pruning, use sharp cutters and seal the wound with sealing paste or something similar. You want the edges of the cut to be clean and not torn. Hollow the wood in the cut a little bit by using knob cutters (rounded blade) or even a Dremel tool. The cambium (thin green layer just under the bark) needs to be kept moist and healthy (that is what the paste is for as well) to allow it to grow and roll over the wound and after time, sealing the wound off for a natural appearance.

The main reason for pruning throughout the growing season is to keep the internodes short, the leaves small and the most important one, increasing ramification. It is also used to create layers or foliage clouds by removing upward and downward growth.

The main refining method is trimming, supplemented with pinching in more established trees. The general convention is that you will prune back to two or four pairs of leaves. This is done when the new branch has extended to three or more pairs of leaves. Sharp scissors are used to cut through the central shoot and leaving a short part of this shoot still intact. Maples do die back where a cut is made. By leaving a short stalk, the die back will not affect the buds from where new growth will sprout.

Pinching is used on well-established tree and is a refinement technique. The new leaves are removed just as they start to unfurl, as early as still in their embryonic stage. If there is a specific area where you want denser growth, remove the leading shoot as well as the two side shoots. The finer leaves will have finer twigs and this all adds to refinement and better ramification. This is what gives deciduous trees and especially Maples, the great silhouette during Winter time when the tree is without leaves.

Large leaves can be trimmed off at any time. As mentioned before, this will allow more light to penetrate through to the interior of the tree which in turn will cause more back budding to occur.

Defoliation

Defoliation can take place by mid-summer as long as you still have a decent length of growing season ahead. As mentioned, this will lead to smaller new leaves growing and will also help to allow more light to penetrate into the tree. This can be done by removing all leaves. Only do this when the tree is healthy and you have good weather conditions ahead. It will take up to three weeks for leaves to grow again. Defoliation can also be used to balance the energy and growth across a tree. If a specific branch is lagging behind, partial leave removal on that branch can help to invigorate the branch. This method is not as invasive as complete leaf removal and allows the branch to grow new shoots. I personally prefer to defoliate over two weeks. I do the lower branches first and then over the next two weeks move up the tree until done. This is less stressful and balances leave growth across the whole tree.

Conclusion

  • Think about and plan structural pruning as well as refinement pruning and pinching.
  • The health of the tree always comes first.
  • Use sharp and clean equipment for cutting and pruning.
  • Prepare and clean cutting wounds.
  • Always use cut paste on larger wounds.
  • Keep the big picture in mind.
  • Make cuttings of the prunings.

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