Best time to defoliate Japanese maple bonsai is mid-summer (as the month of June is ending). At this time all the leaves from the tree can be removed. In 3-4 weeks you should see new leaves emerging from the buds at the base of the leaf stalk (petiole). However, perform complete defoliation only on a healthy tree. With defoliation, you are basically forcing the tree to produce a second crop of leaves in the same season. Only a strong and healthy tree will be able to handle that stress.
Defoliation is an important part of caring for a Japanese maple bonsai, as it helps to promote overall health and shape of the tree.
Important note: Defoliation (also known as ‘leaf cutting‘) is only done on deciduous trees. It should not be done on conifers.
Why to defoliate Japanese maple bonsai
There can be many reasons why complete defoliation of your tree must be required:
- Reduce the size of the leaves. Defoliation will not only lead to the production of smaller leaves but also brighter color. It is not always the case, however. Occasionally, the leaves will not shrink in size.
- Defoliation will also reduce the length between the nodes.
- Force the tree to push new growth. There are two growth flushes on Japanese maples, in Spring and summer. If you are not satisfied with the growth in summer or you notice that the tree has stopped growing, you can defoliate the tree to push new growth.
- Increase ramification and inner growth of the tree. A complete defoliation will make the tree push new growth. The tree will produce more inner growth and increase the ramification of the branches, resulting in more dense and bushier plant. If you are planning to defoliate the tree to promote new growth, do it when the tree has slowed down growing in summer. Some new growth will also happen on the tips of the shoot. If you want to restrict the growth on the tips of the shoots, then perform ‘partial defoliation‘. (Partial defoliation is discussed further in the article)
- Defoliation is also done to remove damaged leaves (eg. leaves burnt due to sun or frost) from the tree and reduce the risk of disease and pest infestation. Continue reading about bonsai pest and diseases.
- Defoliation is also done to provide a clear view of the structure of the tree. It makes pruning the tree and choosing the desired branch structure easy. Continue reading Best way to prune a bonsai tree.
- Partial defoliation also allows more light to penetrate the canopy and reach the inner parts of the tree, promoting new and healthy growth. If left unpruned, the lower and inner branches will become weak.
Defoliation will delay the onset of fall color.
Rather than heavily fertilizing Japanese maple bonsai, performing the right pruning technique and defoliation will accelerate the growth of your tree. Heavy fertilization results in thin cell walls and elongated cells. This will make the tree less hardy especially in colder zones (zones 5-6). Continue reading about how to fertilize a Japanese maple bonsai tree and how to prune Japanese maple bonsai tree.
How to defoliate Japanese maple bonsai
There are 2 ways of defoliating a Japanese maple bonsai tree:
- Using a sharp shear, remove the leaves (you can even pinch the leaves with your fingers). Please read essential and advance bonsai tools. Even if some of the leaves are young or have just emerged, remove all the leaves from all the branches. Because you are removing each leaf one by one, this is a time-consuming process (a medium to large sized bonsai tree will take almost 1-2 hours). You may be able to make the process a little bit quicker with the help of an extra set of hands. Make sure that you are using a clean set of scissors to avoid any risk of spread of diseases. Continue reading how to take care of your bonsai tools. Leave the leaf stalk (petiole) on the branch. The leaf stalk will eventually dry and shrink, and fall from the tree. As mentioned earlier, new leaves will emerge from the nodes right below the leaf stalk in about 3-4 weeks.
- The other method of completely defoliating Japanese maple bonsai is to scrape off the leaves from the branches. This is done by grabbing the branch with one hand and pulling on the branch with the other hand so that you can scrape all the leaves off the branch. However, it is important to note that this method is not generally recommended for bonsai beginners. You have to be very careful and apply the right amount of pressure to just remove the leaves and not break or pull the whole branch off the tree. Furthermore, if you apply too little force, you may not be able to scrape the leaves off the branches. There are different viewpoints about this technique. While some bonsai enthusiasts do not recommend this technique, it appears to work if done correctly. If you have a garden, you can try this technique on a tree planted outside before trying it on your bonsai. The purpose of this method is to save time. If you have time, I would recommend pruning the leaves one by one to defoliate the tree.
Partially defoliate Japanese maple bonsai
As discussed earlier, if the tree has become too bushy, sunlight won’t be able to penetrate through the dense canopy into the inner sections of the tree. This will result in weaker inner and lower growth on the tree. To avoid this, you can perform partial defoliation. Almost half of the leaves are removed in this process. Partial defoliation will also strengthen weak and discolored inner leaves.
Japanese maple leaves grow in pairs. When you start partial defoliation, remove one leaf from each leaf pair. If possible, remove alternating leaves i.e. if you prune the leaf on the right on the first pair, then prune the leaf on the left on the next pair.
Continue doing this on all branches. However, do not do this on weaker branches. Keep the leaves on these branches so that they grow stronger.
Complete defoliation not only encourages new growth in the inner sections of the tree but some of the new growth will also occur at the tips of the branches. Hence, if you want to restrict growth at the tips of the branches, you can perform partial defoliation. Leaving a leaf at the tip of the branch will discourage new growth at the tip.
