How To Repot A Bonsai Tree

Before we get stated I want to point out that this just a general overview on how you should repot a bonsai tree.

Although you will probably use all of the following repotting techniques at some point throughout a bonsai trees life, how much work can be done and to what severity will depend on the species and also at what point the tree is in its development. 

The following information is for general knowledge, don’t use this as an exact guide to repot every tree, use it as a base for your overall knowledge.

You will need to do research on the individual species that you own to make sure you are repotting your bonsai correctly.

On a similar note, I will also say that it is really important to remember that developing your bonsai roots is a long game, not a onetime mission. 

You will repot a bonsai tree many times over the years. You cannot get your roots perfect in one go, it’s the accumulation of repeating these repotting techniques over years that will get you a beautiful root spread. It’s better to be slow and cautious so your tree stays healthy, rather than rush it and kill your tree in one day.

What Do You Need To Repot A Bonsai Tree?

Once you have established that your bonsai tree needs repotted its time to get to work.

(If you are not sure if it is the right time, then read my guide on – When Do You Need To Repot A Bonsai?)  

You should start by getting everything you need ready and have it close by.

You will need the following tools:

• A Root Rake
• Root Scissors
• Soil
• Mesh
• Wire
• Wire cutters
• knife
• Chop stick/Something with a similar shape

(You can read more information about other Beginner Bonsai Tools you might need when doing bonsai)

I would also advise you to repot a tree that is slightly dry. You don’t want the tree to be bone dry, I would wait until it needs watered. Then instead of watering, do the repot. You will find soaking wet bonsai soil is harder to deal with than a soil that is slightly dry.

How To Prepare A Bonsai Tree For A Repot

Take your tools and your bonsai to your work area and now you can get the tree ready for the repot by getting it out of the pot, which if you’ve seen any of my videos can be tricky.

Remove Any Moss From Your Bonsai

If your tree has moss in the pot and you want to keep it/ reuse it. You should remove it and put it to one side. If you are not wanting to keep the moss, you can just remove it and throw it away.

(You can read more about – Should You Put Moss On A Bonsai)

Undo And Remove Any Wires In The Bonsai Pot

If your tree is wired into the pot, or has any guide wires attached from the branches to the pot, these will have to be removed. The tree will not come out of the bonsai pot if you do not remove these anchor wires.

You can access most anchor wires from underneath the pot. You can just cut it with the wire cutters.

I do not wire the vast majority of my trees into their pots, so you will see in my Youtube videos that I do not do this step.

(If your tree has wire on the branches, this can stay on during the repot. To find out when to remove this wire, read this article here)

Remove The Tree From The Bonsai Pot

Now that the wire is removed, you can now remove the tree from the pot. However, depending on the shape of the bonsai pot and how overgrown the roots are, this may be difficult.

I often use my rake to scrape away the top layer of the soil, and the area around the edge of the pot. I find this can give enough space to loosen it up enough to let the whole root ball come out.

If you are using a plastic flower pot, you can give it a squeeze. This will help loosen the root ball from the pot.

If your tree is in a ceramic bonsai pot, you may need to put a knife down the side, in between the root ball and the inside of the pot. This should loosen up the tree and you should be able to get it out.

Some ceramic bonsai pots have a lip, which stops the tree coming out. If this is the case you may need to use your knife or another tool to cut away the roots below this lip. I have found removing the soil from the edge and near the lip can often just free up enough space to squeeze the roots out. However, it is far easier to cut them away.

Removing the tree from the pot can be the hardest part and can be a bit of a struggle at times. Keep going, it will come out eventually.

If you have watched any of my YouTube videos you will see I am constantly struggling to get trees out of the pot.

Clean The Pot

If you are going to reuse the same pot and want to clean it, now is the best time to do that. If you are using a new pot, then you can still clean it if you feel like it needs it.

Your tree will be fine sat out of the pot with the soil still attached to the root ball.

Go and clean your pot now and then by the time you are ready to use it again, it will have dried.

(You can read more about – How To Clean Your Bonsai Pots)

Prepare The Pot For The Tree

Although we have not started work on the tree yet, It is best to get the pot ready, so that when we do work the tree, it can just go straight into the pot with out delay.

You can prepare the pot by adding your tie wires through the bottom holes. You can also place your mesh over the drainage holes.

It is advised to use wire to secure your mesh. However, I have stopped doing this. I have found the wight of soil holds in position, but that’s just me. If you want to wire it in, that’s probably better.

The Pot is now ready to be used again, so this step is very easy.

Remove The Soil From Your Bonsai

Now everything is ready you can actually start working on the roots of the tree, with the first job being to remove all of the soil, by raking it out. Depending on the soil your tree is planted in, it may fall away easier than others.

The amount of roots there is may also affect how easy it is to rake out. It is very common for there to be a huge mat of roots around the outside of the root ball, especially at the bottom.  I always try to use my hand to break these up and loosen these roots first.

Use your rake to rake the soil outwards, away from the centre. This will help untangle the roots and doing it in this pattern will help make sure they are not damaged. Imagine you are combing out some long hair and it should help you with the technique.

You may tear some roots using while raking, and this is fine. They will most likely be crossing roots that would need removed anyway.

Just try and be gentle as you can and tease the roots out, don’t hold the rake tightly. Hold it loosely so you are not ripping too many roots, you are just slowly untangling them.

Why Do We Remove The Soil From Bonsai When Repotting?

We need to remove the soil so we can get everything untangled and see what is actually going on with the root system.

We need to see how they are growing, so we can work out how to prune them. You can’t do this when they are covered in soil.

Also depending on what your soil is made from, you may find that some of the components have broken down, so basically the soil is no longer healthy for the tree. We want our bonsai trees growing in a loose soil mix so they can get plenty of air and oxygen, when a soil breaks down, it becomes compact and is no longer loose, making it not as healthy for the tree.

Removing the soil will allow us to replace it with better, fresh bonsai soil.

Should You Wash The Roots Of A Bonsai?

Once your tree is free of soil you can wash the roots. To be honest, you don’t really need to do this, the main purpose is to clean the roots so you can see what’s going on.

However, if you can get the majority of the soil off by raking, then you shouldn’t need to wash the roots.  If your tree was in really sticky clay like soil, then this may be appropriate.

I’ve found this step isn’t always required, especially if the soil you had been using was of good quality. 

There is also an argument that you are washing away a lot of good bacteria that had formed between the roots and soil, which is also why I don’t like to do it. This is actually very important when you are repotting pines and other conifers as the really need this bacteria and washing it away would not be great for them.

Rake Your Roots Out

Now that you have all the soil off you can start to try and rake everything out and untangle everything. This will allow you see where everything is coming from and will also let you see how long the roots are.

You can now evaluate what is actually going on with your root system and try and work out what needs pruned and just generally see what state they are in.

How To Prune The Roots Of A Bonsai

Now you have all the soil off the roots of your bonsai, and can see what is happening, you can actually start to prune the roots. Always remember its better to be slow and cautious with your root pruning. You can’t do everything all in one go.

I will go through the different type of roots you will find and how you should generally treat them. Hopefully your tree is healthy looking and you can actaully work on it.

If you think your roots may be unhealthy, then you will need to deal with them slighty different. You can read my guide on – What Do Healthy Bonsai Roots Look Like?

Tap Root

If there is a tap root on your bonsai, it needs removed.

How much can be removed in one go will depend on how many other roots the tree has. I have written a more in depth guide on Removing A Tap Root On A Bonsai which will help you deal with that.

Fine Roots

You want to keep as many fine roots as possible. These are the roots that actually take up the water and nutrients.

A bonsai needs these fine roots to live. The larger thicker roots, such as the tap root are mainly for stability and anchoring the tree into the ground. As our tree is growing in a pot, these anchoring roots are not needed and we want to only focus on keeping the fine roots.

These fine roots are also important as a pot is quite small, so there is limited resources available. You want as much of your bonsai pot to be filled with fine roots so they can use up these limited resources effectively.

Thick Roots

You will often find long thick roots, which your bonsai does not really need. Normally you can just remove these, but of course check that they are not the only roots with fine rooting at the end of them.

If you have plenty of fine roots near the trunk, then your tree will not miss the thick root, so you can just remove it

If the only fine roots you have, are at the end of these thick roots, then it’s not going to end well if you remove them. You will have to leave them and hope that finer roots develop near the trunk in the future. If this happens then you can remove these thick roots next time

Crossing Roots

This is more of an aesthetic issue. You want your roots spreading nicely out from the trunk. When they cross over each other it just doesn’t look as pleasing.

Sometimes you can just uncross the roots and straighten them out. In other instances this can not be done, so they will need to be removed.

Radial Roots

In general, you want your bonsai to have radial roots.

This means you want the roots to fan out in a radial pattern from the trunk. If you can imagine how a bicycles spokes come out from the centre of the wheel, you want it to be like that.

If you looked down on your tree from above, you want to imagine your trunk is the centre of the bike wheel and then the roots come out like the spokes.

This is why crossing roots are not wanted and this is also why you want roots to be coming out of your trunk from 365°. If you only have roots coming out from one side the tree will not look balanced.

You Want Only One Root Plane

You want your roots on one plane. If you have a seedling or nursery stock tree, you will often find that there is a number of root planes. You might find a ring of roots then a few inches below that you find another.

For a normal tree this is totally fine, for bonsai, this can’t happen. Once you start getting a tree into a shallow pot, it will be impossible to have roots like this.

You will need to choose a root plan and remove any others. This can be based on looks and which plane seems stronger and healthier.

In the picture above I would remove the top plane. It is ugly and only on one side of the tree. The lower plane is closer to the trunk, with more fine rooting that also seems to come from all around the trunk, which is much more ideal.

You Want Your Roots To Have A Flat Bottom

Following on from having one root plane, you will also need your roots to have a flat bottom. Having only one root plane will help a lot with this. However, sometimes you will find one root that grows straight down.

These can be removed. This is again due to bonsai being in shallow pots. Roots that grow down and roots that are not very flat do not sit properly in shallow pots.

How Much Can Remove When Pruning Bonsai Roots?

How much you can remove really depends on the species and the individual tree and it really is a balancing act.

Some trees can take some extreme root work and if you’ve seen any of my youtube videos, you will know that I will try to push my luck with how hard I prune. I have owned my trees for a number of years and I know how much work they can handle.

You should aim to keep as much fine roots as possible. The more of this that you can keep, the better chance your tree has of survival.

You should try and shorten as much as you can, but also try and balance it so that you can leave as much as fine rooting as possible. If you are unsure how much to remove, be cautious.

If you have not worked with the species before or you do not know how they react, you should trim conservatively. You will then get an idea how the tree responds and can change your approach accordingly the next time you repot.

You do not need to go crazy, you can develop your roots over a number of years. You need your tree to survive this operation, so do not push it if you have any doubts.

Balancing The Root System Of A Bonsai

When you are pruning the roots of your bonsai you always want to make sure you are balancing the root system.

The roots are exactly like the branches. You do not want one area being far stronger than the other. You need to look at the whole root system as a whole and make sure everything is as balanced as possible. This may mean pruning one side more than the other, or leaving an area alone so it can grow more.

If you balance your roots properly you should end up with a very good root ball in a few years. You can read more about Developing A Nebari (Spreading Roots) where you will find a lot of what I talk about here, with repotting …this is what actually gets you a good root spread on a bonsai.

Put The Bonsai Tree Back In the Pot

Now you have pruned your bonsai roots you can pot it back up and finish up the repot.

Test Fit The Tree In the Pot

The first thing you need to do is make sure your root system will actually fit into the pot you are putting it in to.

Just take the tree and place it in the pot. You will very quickly realise if the tree is going to fit or not. While some bonsai pots may be snug, you should still have enough room for the tree to grow into.

bascially if the roots are already touching the sides of the pot, its probably not a good fit.

You can either remove more roots until it fits into the pot, or you can just use a larger pot. This will depend on how aggressive you’ve already been on the roots. If you think it would be dangerous to remove some more roots, then you need to use a bigger pot.

Add The Soil And Tree To The Pot

Now that we know the tree will fit into the pot, we can add the bonsai soil.

Pile it up in a mound in the middle of the pot. The mound should reach to just about the top of the bonsai pot.

Place the tree on to the top of the mound at the angle you want. Push the tree down and wiggle it around ever so slightly so that soil is fully touching the underside of the tree.

You can add or remove soil until you are happy with how your tree is sitting in the pot. Make sure you have the desired front facing where you want it, and make sure your tree is at the right angle.

There are all sorts of rules on where exactly your tree should sit in the pot. Off centre, more towards the back and leaning slightly forward. These rules are more aimed towards developed bonsai and also depend on the individual tree, its species, its style and the shape of the pot. If you are just a beginner I would not get to worried about these.

Focus on just putting the tree in the pot at an angle and position you like for now.

Once you are happy with where it is placed, use the wires to tie the tree in.

Then fill the rest of the pot with soil so that everything is covered.

Get Rid Of Air Gaps In The Soil

Now That the tree is in the pot and covered in bonsai soil, you need to make sure there is no air gaps in the soil.

You need poke the soil with a small stick, chops sticks are excellent for this and I also like to use cocktail sticks for smaller pots.

Poke the stick into the soil and rotate it in a circular motion. You will see the soil will start to fall into the area you are moving the stick.

This may seem strange, but basically you are making sure there are no air gaps in the soil. Using a stick makes sure there are no hidden pockets. Large air gaps can stop water getting into that area and cause it to dry out. You don’t want dry patches in your pot as this can damage the trees health.

As you wiggle your stick you will find that the soil level goes down. So you will need to top up the soil as you go.

Once you are happy  all the air gaps are removed and the pot is full of soil, you are pretty much done.

Adding Moss To Your Bonsai

If you are adding moss to the pot, now is a good time to do it.

You can read my guide on How to Moss a Bonsai for the best way to do this.

Watering A Bonsai After A Repot

The last step is to thoroughly water your pot. When you start watering you will start to see the water coming out of the bottom.

This water will be brown and cloudy. This is just all the loose particles of soil being washed out. Keep watering until the water goes clear.

I have more information – How To Water A Bonsai After Repotting – where you will find more details about how to do this properly.

Repotting After Care For Bonsai

Your tree is now repotted but it will still need close care for the next few weeks until it has recovered.

Keep the tree somewhere safe, so it does not get knocked over, or blown over by the wind. Although you have tied the tree in, it can still be unstable. Until it has grown new roots and gripped on to the soil, it is in danger of being knocked over, so protect it for a few weeks.

You must also make sure the pot does not dry out. Just like normal, but you need to be aware you freshly trimmed roots are more delicate than normal, so you need to be extra vigilant.

you may also need to keep the tree out of direct sunlight for a couple of week, or at least limit the amount of direct light it gets. The tree will not have the root system to cope with the water demands that being in full sun will require.

I also have a more detailed guide on this topic, which you should read, as this part of the repot is actually very important to your trees survival – Repotting Aftercare Advice For Your Bonsai.

Fertiliser

You should not fertilise your bonsai for about 6 weeks after repotting. Again this is because the recovering roots will not be able to handle it and it will actually harm them.

You can however use tonics that are designed for stressed and weak roots, such as Rhizotonic. These help the roots recover faster, so if you can, you should use these.

(You can read more about – What Are Some Common Mistakes To Avoid When Repotting A Bonsai?)

Conclusion

Okay, so this was long and a lot of information, but you should now have all the details you need to repot a tree successfully.

Once you do it a few times you will realise its very easy and actually a lot of fun. Just take you time and go easy on the root pruning if you are not too sure how it will react.

After a few weeks your tree will start to recovered, you will see that it is growing and should look healthy. You can now look after your tree in the normal.

(You can read more about – Frequently Asked Questions About – Repotting Bonsai)