Without a doubt, the most important way to train a Bonsai is to prune it regularly. There are two different techniques: Maintenance-pruning, to maintain and refine the existing shape of a Bonsai, and structural-pruning, which involves more rigorous pruning to give a tree its basic shape or style.
Before discussing both techniques in more detail, it’s helpful to get a bit more fundamental information on how trees grow. This will help us understand how to prune Bonsai trees Bonsai trees efficiently.
Trees have a natural tendency to grow with apical dominance. This means that the main, central stem of the plant grows more dominantly than its side stems. For example, on a branch, the main stem of the branch is more dominant over its side twigs. This natural mechanism encourages trees to grow higher to prevent them 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, both of which are not desirable traits for Bonsai aesthetics.
Knowing the natural growth patterns of trees tells us how we can use pruning techniques to counter the effects of apical dominance. Because dominant growth occurs on a trees’ central stems, we know we have to prune the top and outer portions of a tree more thoroughly. This forces the tree to redistribute growth to the inner and lower parts, which gives us control over the growth and design of the tree.
The goal of maintenance pruning is to maintain and refine the shape of a tree. As explained above, trees will concentrate most growth on the top and outer parts of its stems; it is important to prune these growth areas regularly to encourage growth closer to the inner parts of the tree.
Maintenance pruning can be done throughout the growing season, usually from March to September for outdoor Bonsai. Indoor Bonsai can be pruned year-round.
As previously mentioned, maintenance pruning is required to maintain a trees' shape. To do so, simply prune branches and shoots that have outgrown the intended canopy shape using twig shears or normal cutters. Using the right Bonsai tools will help significantly. Don’t be afraid to prune your Bonsai regularly, it’s important to force the tree to distribute growth more evenly and develop dense foliage.
Pine trees and some conifers should be pinched by hand rather than cut with scissors. Using scissors, cutters, or shears to prune some species of conifers can lead to brown, dead foliage at the cuttings. 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 you will avoid brown or dead ends. Different species need different maintenance regarding pruning and pinching; some even need a combination of both. Please consult our species guides for information per tree species.
Another method of Bonsai pruning is defoliation, which involves removing leaves of deciduous trees during the summer to force the tree to grow new leaves. This technique is used to reduce the size of the tree’s leaves and increase ramification.
Giving a tree its basic shape often involves pruning large branches. Deciding on which branches should stay and which ones should be removed can be a difficult choice. Not only because it is an irreversible action but also because it will define how the tree will look. Before rushing into techniques used for pruning Bonsai, we recommend taking a look at the Bonsai progressions section. You‘ll find great references and examples of experienced Bonsai artists structure-pruning nursery stock.
Generally speaking, the best time to structure-prune a tree is in the early spring and some cases late autumn, just before and after the growing season. The exact timing differs from species to species. In the tree species section you can check the specifics on your particular tree, a Ficus Bonsai needs different timing from a Juniper Bonsai for example.
Place your tree on a table and position yourself at eye-level with it. Begin by removing all the dead branches from the tree. Once that’s done, take a close look at your tree and decide which branches need to be removed to create your desired design. We’ve provided a few guidelines in the image below, but designing your tree is more of a creative process and not something bound by 'rules.'
Pruning thick branches typically result in ugly scars but by using special concave cutters you can reduce scaring effects significantly.
A healthy tree should have no problem coping with the pruning of up to 1/3 of its foliage. Some say you should cut/remove an equal percentage of roots after a tree has been styled. However, most experts advise only performing one big maintenance at a time (or even once a year). For example, if you structure-prune this spring, you should wait to do any repotting or root cutting until the next spring when the tree has fully recovered from the structure-pruning. Take a look at the root flare (Nebari) page for more details on pruning roots.
Finally, we advise sealing large wounds with cut paste, available at most online Bonsai shops. The paste protects the wounds from infections and helps the tree to heal faster. Again, using the right Bonsai tools will help significantly.