Pruning is not only used to train and shape a Bonsai but also to maintain its existing shape.
During the growth season it is important to regularly prune you trees, this will help them to grow a more dense foliage and distribute growth from the top area of the tree to the lower parts.
Without doubt the most important way to train a Bonsai is to prune it on a regular bas.
Essentially, there are two different techniques: maintenance-pruning, to maintain and refine the
existing shape of a Bonsai and style-pruning, which involves more rigorous pruning to give a tree its
basic shape or style.
Before handling both techniques in more detail it is wise to look at some background of how trees
grow to help us understand how to prune a Bonsai.
Trees have a natural tendency to distribute most growth to the top and outer edges, which is called
‘apical dominance’. This natural mechanism encourages trees to grow higher in order to prevent the tree from being shaded out by competing trees. By distributing growth to the top and outer edges the tree’s inner and lower branches will eventually die while top branches grow out of proportion; two
effects not desirable for Bonsai trees.
This basic background reveals not only the importance of pruning in general but it also teaches us
to counter apical dominance by pruning the top and outer portions of a tree slightly more thoroughly.
Maintenance pruning
Important for maintenance pruning is to maintain and refine the shape of the tree. As explained above trees will concentrate most growth on the top and outer parts of the tree; it is important to prune these growth areas regularly in order to encourage growth closer to the inner parts of the tree.
When? Maintenance pruning should be done during the entire growth season
How? In order to maintain the tree’s shape cut shoots through the stems just above a leaf. Do not be afraid to prune your Bonsai; it is important, especially in the outer and top areas, to prune regularly in order to force the tree to distribute growth more evenly and develop a dense foliage.
Instead of being pruned, pine trees and conifers should be pinched by hand. Using scissors to prune conifers would lead to dead brown foliage at the cuttings (see photo 1). To prevent this from happening hold the tip of the shoot between your thumb and pointing finger and carefully pull it away; the shoot will snap at its weakest point and no brown ends will appear (see photo 2).
Another method of maintenance pruning is defoliation, which involves removing leaves of deciduous trees during the summer to force the tree to grow new leaves. This technique ultimately leads to a reduction in leaf size and an increase in ramification. For more information check the defoliation page.
Style pruning
Most often, to give a tree its overall shape larger branches will have to be removed. Deciding on which branches should stay and which ones should be removed can be difficult, not only because it is an irreversible action but also because it is part of deciding how the tree will look like.
Before learning more about the techniques used for style pruning you might want to take a look at the case studies part of this website, where you will find examples of experienced Bonsai growers style-pruning nursery stock.
When? Overall, the early spring or late autumn (just before and after the growth season) is the right
time to style-prune a tree.
How? Place the tree on a table at eye-level; first step is to remove all the dead wood from the tree. Now take some time to observe your tree and decide which branches do not fit the desired design and will need to be removed.
A few basic guidelines:
- If two branches occur at the same height of the tree, keep one of them and remove the other.
- Remove vertical growing branches, which are too thick to bend.
- Remove branches with unnatural twists and turns.
- Remove branches that conceal the front of the trunk.
- Remove disproportionately thick branches from the top of the tree, as branches at the bottom
should be thicker than at the top.
Pruning thick branches will result in creating ugly scars on the tree, but by using a special concave cutter you will reduce this effect significantly because of the indentation it makes when cutting off the branch.
A healthy tree should have no problem coping with pruning up to 1/3 of the trees foliage. However, when pruned significantly, it is important to prune the roots back in equal proportions. This way you prevent the tree from developing a rapid growth to fix the imbalance between the amount of foliage and roots. More details about pruning roots can be found at the root flare page.
Finally, it is advisable to seal large cuttings with wound paste, available at most Bonsai shops. The paste protects the wounds against infections and helps the tree to heal faster.
And then? Aftercare
After a tree has been style-pruned place it in the shade and out of the wind. Fertilize as you would do normally and let the tree recover from the training for at least a few months.