What Is Defoliation In Bonsai?

Defoliating a bonsai is an advanced technique that is used to reduce the leaf size of a refined tree.

It can be extremely effective, but it comes with a risk, so it is best that you fully understand why we do this and when it appropriate, to make sure you get the best response from your own tree, which I will go through here.

What Is Defoliation?

The technique of defoliation is pretty simple; you just remove some …but usually all of the leaves of your tree.

If we look at the word, it makes sense. The leaves are often referred to as foliage, and the de- comes from Latin, meaning to remove or take away … so the word literally means – remove leaves.

Of course you need to know why we do it and when, which I will discuss below, but very the basic principle is to just cut the leaves off your tree. 

Why Do We Defoliate Bonsai?

Everything we do in bonsai has a reason and defoliation is no exception. The point of this technique is to produce smaller leaves on our trees.

When a tree reaches the refinement stage it will really start to look a bonsai, the whole structure can really start to look like a full size tree in miniature.

However, often our trees are actually very healthy and you may find they push out some strong growth in spring. This usually means the leaves may be a little larger than we want, they are probably going to still be quite small, but perhaps we want them to be even smaller to make them really look in scale with the rest of the tree.

If this is the case, then defoliation is the answer. When we remove the leaves it forces the tree to react and replace what it has lost. The leaves are like the solar panels for the tree and produce its energy, so the tree will not be very happy that they are missing and will make it a priority to replace them.

Now that the tree is not currently producing energy …since we removed all the leaves, the tree has to use its energy storage reserves. This means that the tree does not really have the optimum level of energy to produce new leaves. This sounds bad, but it’s actually perfect as it means the new leaves end up being smaller.

We are literally taking advantage of the trees weakness to get smaller leaves. Once the leaves grow back, the tree will be able to operate normally again, it’s just that we now have the desired look of smaller leaves.      

It is common for people to defoliate a tree a few weeks before a show, so that by the time the show starts the leaves are looking very small, and the tree will look more impressive. 

When Can You Defoliate A Tree?

Ideally you want to do this is late spring or early summer. Most people suggest around June, which is about right. 

You want the spring growth to have fully grown and hardened off before removing it and more importantly you want to make sure there is enough time left in the growing season for the new leaves to grow back. 

How Often Should You Defoliate A Bonsai?

Defoliating a tree can really knock the wind out of it; you are dipping into the energy reserves, so really this technique should be used sparingly. Doing it too often can significantly weaken the tree.

Really you need to make sure you tree is healthy enough to handle the procedure and more importantly you need to make sure it has time afterwards to recover.

You need to take into account what other work you have done to the tree recently. Pruning and repotting a tree usually knock some vigour out of the tree, so it may not be wise to defoliate if you have done on of these things recently.

Generally you will find most people defoliate only once during the growing season and it is also not done every year.

While a year is a long time, the tree may still be weakened from what you did to it last season, so it can be best to not defoliate it every year. This would be especially true if you tree is old, although a younger tree may have more vigour and may be able to handle it more often.

What Trees Can You Defoliate?

You cannot defoliate all trees. You will need to look up your individual species and see if it can handle it or not.

It is important that you check this as if the tree cannot handle it; you are going to severely weaken it and maybe kill it. At the very least it can really disturb the energy distribution of your tree and you will find some leaves grow back small, while others are massive.

Trident Maples

I just want to mention tridents are they are sort of the exception to everything. They can be defoliated and while I warned above that you shouldn’t do it too often, tridents can seem to handle it. People often defoliate them every year and even sometimes a few times within the same growing season.

They are just extremely robust. I would still be cautious, but you will find they are more vigourous than a lot of other species.

(You can read more about – Is A Trident Maple A Good Tree For Bonsai?)

Is There Any Downsides To Defoliating?

The only real downside is that you weaken the tree, but of course the trade off is that you are getting the smaller leaves so it’s a balancing act when it comes to deciding to do this. 

As I already mentioned, doing this too often, or to the wrong species can be damaging for the tree, but overall it is worth doing and it can be a part of a balanced and healthy trees life.

I’ve also mentioned it throughout, but I will be clearer here …This technique is really only for a refined tree. If you tree is in development then you should not be doing this. There is no benefit to having a tree with smaller leaves apart from aesthetic reasons, which a tree in development doesn’t need.  You are better off focusing on waiting until your tree is more refined before doing this.   

What Is Partial Defoliation?

A partial defoliation is when you remove some of the leaves, or you just trim the leaves, so you basically cut them in half. 

This is a sort of less extreme version and most trees can tolerate this a lot better.

However, we do this for a slightly different reason. This is done to allow more light into the centre of the tree.

Most branches have buds along them, even if you can’t always see them, they will be there. This is a good thing as it means we can cut a branch back and then it will regrow from one of these inner buds. However, some trees get pretty dense canopies and this can block the light to the centre of the tree, which in turn can kill off those inner buds.

We partially defoliate to allow some light in to this area. Just removing a couple of leaves here and there or cutting the leaves in half can drastically thin out a canopy and allow more light in, keeping those inner buds nice and healthy in case we want to use them one day.

As you are only remove some leaves, or just cutting some leaves in half, the tree is not really stressed by this, so you can do this more often and it doesn’t really weaken the tree, in fact it keeps it healthier as the roots are now having to support less leaves, as well as the benefit for the inner buds that I have already discussed.   

Is Partial Or Full Defoliation Better?

If you look at the two explanations for why we do either technique, you will see they are for very different reasons, this means you can’t really compare which one is better as they are so different.  

The one that is better is the one that is going to achieve what you want. If you want smaller leaves then defoliate fully, and if you want to let light into the centre of the tree, then partially defoliate.

Conclusion

Hopefully now you understand what defoliation is and why we use it. It can be a very good technique, but only if done at the right time and on the right trees.

You really shouldn’t be using it all that often, but there will be a time and place for it, so it’s good to have it in your back pocket for when the time is right.