How Do Bonsai Stay Small?

Bonsai trees are just miniature versions of full size trees, but what keeps them so small and why do they not grow to their full size?

Basically a bonsai tree stays small because its growth is manipulated in a way that keeps it small and stops it from ever reaching its full size. We control where the energy of the tree goes and we do not allow it to to big.

It can seem quite complicated, but some simple bonsai techniques will control the trees growth in a way that keeps it small.

How Do You Make A Bonsai Stay Small?

To keep a Bonsai small you need to control the growth of its roots and its foliage. If you can manage these properly the tree will remain small.

The real goal is to never allow the tree to get too big in the first place. We do this while also balancing the trees health and vigour so that the although the tree is small, it will always be very healthy.

I will go through some of the main techniques we use to do this below, which will explain how we keep a bonsai small.

Some people mistakenly think these techniques are bad for the tree and say its cruel, but it is not. We just control the distribution of the energy.

(You can read more about how that is not true – Is Bonsai Cruel?)

Controlling The Roots Of A Bonsai To Keep It Small

The main difference between a full size tree and a bonsai tree is the root system. Bonsai are grown to have a small dense root ball that is full of fine feeder roots, while a full size tree will send out thick long roots that anchor it into the ground, which we don’t need in a small bonsai pot.

Root Pruning A Bonsai Will keep It Small

Having a small root system that is regularly pruned is one of the main ways to keeps a bonsai small.

The root system of any tree is like the engine. If we keep this engine small, the tree is never going to be able to get large.

The roots supply the tree with the water it needs to be able to grow and expand. As the root ball in bonsai is pruned and kept small, the amount of energy that the roots can supply into the tree will be limited.

How Root Pruning Keeps A Bonsai Small

The biology of a tree is very complicated and also very clever. It is able to work out what resources it has available to it and then is able to distribute these evenly across the tree.

This distribution of energy is why a bonsais growth is in proportion with it size.  

If this didn’t happen, pruning the roots would be a waste of time as the tree would just try and grow a thick/tall trunk like it normally does when grown in the ground. This would end badly for the bonsai, as it would not have the root system to support this larger growth.

By pruning the roots of a bonsai we are forcing it into having less energy to distribute to the rest of the tree. As we know it will distribute what energy it has equally through the tree, we know we will get smaller, but proportionately sized growth. This smaller growth is what we want in bonsai and it is our job to manage this and balance it properly.

We see can actually this process happen all the time in nature. Trees that have limited resources, like those growing in a small crack on the rock face of a mountain, will be always be small as they have limited resources. Especially when compared to a massive tree that is growing in an open field, which has access to unlimited resources.

Bonsai Pots Make A Bonsai Stay Small

The size of a bonsai pot also plays a huge role in keeping a bonsai small. Although we regularly prune the roots, this on its own is not enough.

If we pruned a trees roots and placed it into the ground, it would soon recover and stretch out to its full size again. Keeping a tree in a small pot restricts the space that the roots can grow in to.

A bonsai pot can only contain a limited amount of resources for the tree. There can only be so much water and oxygen in a pot at one time for the tree to use. As I said above, the tree is able to work out what resources it has available to it and then is able to distribute these evenly across the tree.

This supply of limited resources is going to help keep the bonsai small, but of course we need to balance this by making sure the tree is healthy and always has access to these resources (which means always making sure you water the tree)

If you want your tree to stay small it is important to try and get it into a small a pot as possible and correctly manage its growth through root pruning and pot size

Creating A Small Root System On A Bonsai Takes Time.

It is important to know that this process cannot be rushed. A small root system needs to be created over many years by pruning and gradually reducing the pot size. This will build up a small but very effective root system that is full of fibrous roots that are able to support the tree.

If you just cut the roots off a tree to just fit it in a small pot, it will not have enough of a functional root system to support the tree. As there is not much space in the pot, this heavily trimmed rooted system will not be able to get enough resources to recover and will die.

This is why it can take years to develop a bonsai and why the balance of keeping a bonsai small, but alive, is very difficult.

(You can read more about – How To Go From A Large Pot To A Small Bonsai Pot)

Controlling The Top Growth Of A Bonsai To Keep It Small

Pruning the top of bonsai plays a major role in keeping the tree small. If we can manage its growth properly it will really help keep it small.

Why Do We Need To Prune Bonsai Trees?

Trees like to grow by elongating outward. The new growth always happens at the tips and this is where all the energy is sent.

The tree is trying to put its energy into growing these tips so it can produce more leaves.

Leaves are the solar panels which produce more energy for the tree. The more leaves a tree has, the more energy it can make, and then the bigger it can get.

We need to prune our bonsai or they are just going to keep getting bigger and bigger.

How Does Pruning Makes A Bonsai Tree Smaller?

When you prune a bonsai you are basically removing the growing tips and the tree isn’t very happy about it.

When this happens the tree uses its very complicated and clever biology to sort the problem out. It basically gets annoyed that it doesn’t have the leaves anymore, so it forces the branches to grow more leaves.

It does this by sending all sorts of hormones up and down the tree and the result is that buds lower down on the branch are activated. These buds where previously dormant as the tree bypassed them in favour of sending the energy up to the growing tips at the end of the branch.  

The tree has to use some of its stored energy to activate this process. So by pruning a tree, you are forcing it to use some of its resources. This means the new growth ends up not being as strong, which means it is often smaller, which is of course ideal for bonsai.

     

Pruning Builds Smaller Branches On A Bonsai

The pruning process actually activates a number of these dormant buds, rather than just have one growing tip like before.

These new buds will grow into new branches and the fact that a number of them start growing after pruning means we are pruning one branch and turning it into more.

As a tree will try and distribute its energy out equally, all of these new branches will be sharing the energy that would have been focused into the one growing tip. This means that these new branches will not be as strong and will be smaller.

This is pretty much the fundamentals of bonsai training. By using the trees biology in a controlled way we can make it produce smaller and smaller growth and the end result is a smaller tree.    

(You can read more about – How Do You Build Ramification On A Bonsai?)

Defoliation Can Keep A Bonsai Small

Defoliation is another pruning technique used on certain species to help keep a bonsai small. This is the process of removing all the leaves from the tree. This is like an extreme form of pruning.

In a similar way to when you prune some of the leaves off, the tree reacts by sending out new leaves at all the dormant buds on a tree.

When you prune a tree, you only remove the growing tips. There is still foliage left on the tree to sustain it. In a defoliation, the tree no longer has any leaves and no way to make new energy.

This means that the tree has to use a lot of its stored energy to produce new leaves across the whole tree, it has no other option as there are no other leaves to help support this process.

This is why defoliation is more extreme than pruning. Only certain species can actually handle this and it is also really not advised to do this for a number of years in a row. The tree will be seriously depleted of resources from this procedure.

However, when the tree does regrow, the leaves will be very small and the ramification will be increased across the tree.

Carefully using this technique on a bonsai is going to really help keep a bonsai small.

(You can read more about – What Is Defoliation In Bonsai?)

Pruning A Bonsai To keep It Small Takes Time

In the same way that we balance the roots of our bonsai, we must keep the pruning balanced too. If we just continually prune the tree, it will keep using its energy reserves to push out new growth which will eventually weaken it too much.

We need to let our trees grow and recover some times. The leaves need to grow so they can send energy back into the tree.

Letting a bonsai grow unchecked for a while will allow the tree to build up the energy it needs to sustain itself and replenish the energy reserves that were used after pruning.  

keeping a bonsai small is all about the balance of keeping it healthy, while also trying to keep it small.

Other Factors That Allow A Bonsai To Stay Small?

Sometimes there are just some other factors that help keep a bonsai small.

Using Naturally Small Trees For Bonsai

If you look at the species being used for bonsai, you will see there are a small number of species that get used time and time again.

These species are just naturally better suited for bonsai. They have naturally smaller leaves, or they just generally grow smaller. These trees will also respond far more favourably to bonsai techniques compared to other species.

Using species like this helps us keep the tree small. The tree works with us and getting it to stay small is pretty easy.

Some Bonsai Have Better DNA

As I’ve just said, Some trees are more naturally suited for bonsai and in Japan these more ideal trees have been further refined over the years through selective breeding, to produce even smaller leaves and even better bonsai.

This is why trees like Japanese maples are started from cuttings from trees with ideal foliage and not from seeds. The DNA in the cuttings will be identical to the mother tree, where as a seed could potentially have different DNA and produce coarser leaves.  

Limiting Fertiliser To Keep A bonsai Small

Fertiliser is basically a mixture of nutrients added to the bonsai tree, which help it grow better. The main nutrient that helps leaves grow is nitrogen.

 An increase in nitrogen levels can give you bigger, stronger leaves with larger internodes.

This is great if you are trying to grow your tree larger, but if you want it to be smaller, giving it something that will make it larger is a bit counterproductive.    

Bonsai trees will need fertiliser at various points throughout their lives. It is essential to help with overall health. However, at certain times, fertiliser should be limited to help produce smaller leaves, or at least fertiliser with lower nitrogen should be used.

What Happens If You Stop Using Bonsai Techniques On A Tree?

Everything I have discussed above is designed to keep a tree small, so it will be no surprise to find that if you stopped doing these, the tree would just grow into a full size tree again.

You could plant a bonsai in the ground and within a few years it would just look like any other tree. A bonsai is really only small because we have manipulated to be. We control how it grows and how it uses it energy and the result is a small tree.

If we stop this, the tree will just grow as it wants and end up being full size.

Conclusion

As you can see there is a number of different factors that can affect the size of a tree. Being able to keep a bonsai small is not determined by one of these factors alone.

To keep a bonsai small you must carefully balance all of these factors and also keep the tree healthy and strong at the same time.

If you get this balance right you bonsai tree will be strong and healthy while still looking small and in proportion.

(You may also be interested in reading – How Long Do Bonsai Trees Live?)