What is bonsai defoliation?
Defoliation as a bonsai technique is a method of cutting off part or all of the new leaves that have grown in spring, leaving the tree bare, and allowing new leaves to sprout again.
As bonsai defoliation is drastic and very stressful for trees, not every tree can withstand the process. Defoliation will kill the trees if it is done to tree species with poor regenerative power or to an already weakened tree. Or, if defoliation is not done at an adequate time of the year or the defoliated trees are not well treated, new leaves will not sprout.
So why do defoliation?
Why bonsai defoliation?
The main reasons for bonsai defoliation are;
- To encourage ramifications,
- To reduce leaf size,
- To improve autumn colors,
- To enjoy new leaves,
- To control growth vigor,
- To improve rooting of repotted bonsai, and
- To premature bonsai trees.
With bonsai defoliation, you can artificially create the defoliation phenomenon that occurs only once a year in nature. By repeating this process a few times a year, bonsai trees experience spring several times a year, producing new and fine branches each time. Defoliation is a shortcut to increasing the branching within a year that would otherwise take several years.
On the other hand, there is a limited number of times that defoliation can be performed on bonsai trees in a year since their energy is limited. Bonsai trees usually have the amount of energy to shed leaves only once a year.
They, therefore, need to be very well fertilized and able to store enough nutrients to endure defoliation. If done too much, the stored nutrients within the trees will be completely used up, and the leaves may not sprout again.
Reduce leaf size
A bonsai tree should have small leaves to make it look like a big tree. Branches must be shorter to achieve overall consistency as well. There are various ways to make leaves smaller, such as restraining water and fertilizer and putting in small and shallow pots.
But By far, defoliation has a much greater effect in a short period of time. Defoliation leads to less photosynthesis and energy. As the tree vigor is suppressed, bonsai trees grow smaller leaves and branches with short nodes. Defoliation is an indispensable process in bonsai to grow finer branches and keep the whole tree small.
Defoliation is mainly performed on deciduous trees but also on coniferous trees like black pine. If some of the old pine leaves are removed or pruned before the new leaves grow in spring, they will have fewer leaves with smaller/shorter sizes.
Improve autumn colors
The leaves that come out after defoliation are soft with thin layers of cells, which makes leaves susceptible to temperature changes for color change. Defoliation at the right moment is important because the sugar in the leaf cells will not be sufficient enough to produce anthocyanins (red pigment) if the leaves are taken off beyond the appropriate time. Autumn leaves need anthocyanins (red pigment) for bright red color.
Enjoy new leaves
The green color of new shoots is graceful and beautiful. Depending on the species of maple, for example, there are some trees whose new leaves are red, which we can enjoy. By defoliating, you will be able to enjoy new leaves more than once a year.
Control growth vigor
Leaves are one of the essential organs for life support for plants, and the enrichment of leaves directly leads to tree vigor. Getting rid of leaves thus reduces the strength of the bonsai trees. The next leaf grows smaller and the branches finer.
If defoliation is done partly to vigorously growing branches, tree energy goes to weaker branches, thus averaging the overall tree vigor.
Improve rooting of repotted bonsai
You may sometimes have to urgently repot a bonsai tree that missed the normal repotting season. Or, you bought a new bonsai tree after repotting season but you want to repot it anyway.
In such cases, all or part of the leaves can be defoliated to reduce transpiration. Bonsai repotting entails some kind of root pruning to regenerate the root system and/or to make it fit in the new pot. Though water in plants is constantly lost by transpiration through leaves, pruned roots might not take in water as much as the tree needs.
Rooting will revive if the temperature is adequate and the roots are in the growing season.
Premature bonsai trees
Deciduous trees lose their leaves once a year in fall unless something unusual occurs. When plants lose a lot of leaves due to disasters, air pollution, insects or animal feeding damage, they try to maintain the number of leaves by growing new ones in order to survive.
Normally, only one cycle of growth is achieved in one year. By forcibly removing the leaves and growing new leaves again, bonsai trees experience two cycles of growth in a year. Defoliation may encourage the bonsai trees to premature at an early stage of their growth.