What Are Some Common Mistakes To Avoid When Repotting A Bonsai?

Repotting your bonsai is something you are going to need to do at some point and you of course want to do it properly so that your tree can stay healthy.

However, if you look at when most people’s trees die …its usually after a repot, which means a lot of people are messing this up and this is not what any of us want, so I will be going through some of the most common mistakes I see all the time and hopefully you can avoid these going forward.

Repotting At The Wrong Time Is A Huge Mistake

One of the biggest mistakes you can make is repotting at the wrong time of year.

I go on and on about repotting in spring, just as the tree is waking up and this is for good reason. Doing it outside of this window can actually be detrimental to the tree and can put it a very high risk of death …so it is not worth it.

When you do it at the right time, the tree doesn’t even notice.

If you stop and think about what is happening it makes a lot of sense. The tree is dormant over winter. It has all its energy stored in the roots and as it wakes up, it sends this energy up into the tree.

Repotting Too Early

So, if you decide to repot too early, you are basically going to cut the roots and remove a lot of the stored energy …so how is the tree supposed to burst into life in spring!

Most of its energy is gone and you will see a very poor push of spring growth because of this.

Repotting Too Late

If you decide to repot after this window, it is equally as bad. The tree will now be actively growing and in the middle of the growth cycle. The leaves will be sending energy down into the roots and the roots will be sending water up into the tree. The cycle is of course beautifully balanced and as this goes round and round the tree gets bigger.

If you decide that you now want to interrupt this and chop some roots off …you will upset the balance a lot. The top of the tree is going to push energy down …this is fine, this can help make new roots.

However, there are no roots to support the top of the tree. The leaves need water and you just removed the roots, which provide the water …this can cause a lot of trouble. The smaller root ball can no longer support the top of the tree and you can severely weaken a tree and it can die. 

Repotting At the Right Time

If we look at repotting at the right time we can see we get around both these problems perfectly. The tree has sent all its energy out of the roots and up into the tree. This means we can safely remove roots and no energy is lost …the energy is already in the buds, which are literally about the open.

The tree is also not actively growing …it is days away from doing this, but right now it is not. This means there is no demand on the roots. The top of the tree is not demanding water and even when the leaves so open, and this starts happening …it is manageable.

The roots you have left can still handle supporting a few new leaves. As the leaves grow, the roots will too. Everything will grow in balance, which is not the same as repotting in the middle of the summer when the tree is covered in foliage and expecting 100% of their water needs right there and then.

(You can read more about – When Do You Need To Repot A Bonsai?)

Repotting For No Real Reason Is A Mistake

Another common mistake I see around repotting is when people just do it for the sake of it, there is no real reason behind it.

This is often the same people who repot on a timescale. They see its spring and just assume it’s time to repot.

This is not ideal and you really need to be able to ask yourself why you are wanting to repot. The only two reasons you should give are for the trees health and for its aesthetics.

The health is obvious enough, if the tree is struggling because it is root bound or the soil is dreadful, then a repot makes a lot of sense. This is probably going to be the reason for repotting in most cases.

You can also repot for the aesthetics, which may mean you want to work the roots to get them under control, or you want to replant the tree in a way that shows off more of its roots. Usually you will want to repot a tree slightly more often when it is young to get its roots under control …but in most of these cases the tree will have grown like crazy as its young and vigours, so it will need a repot for health reasons too.

When you tree is more refined and slightly older you may repot for aesthesis to show more of the nebari(root spread), or get it into a certain pot, but really for the majority of trees at this age, you will be repotting to keep it healthy. 

If you are satisfied your tree needs repotted for health reasons or aesthetics, then this is fine… if you are just repotting for no real reason …you should wait.

Working The Top Of The Tree And Repotting At The Same Time Is A Mistake

Doing any sort of work to a tree will stress it out …and the less stress you can cause the better, doing this will allow your tree to heal faster and stay healthier. This really means that you should be spreading your work out over time.

A huge mistake I see is people pruning the top of the tree and then repotting at the same time.

You are attacking the tree both ends, this is going to be hugely stressful and while many trees can be strong enough to deal with this …why put them through it.

I am not saying you can’t do both …just space it out. Prune the top then come back two weeks later and do the roots. Even a small window like this is going to give the tree time to recover a lot. For some species like junipers, you will probably need to space this work out over a full season. These trees are sensitive to work and doing both the top and bottom is too much stress for them.

If you also think about the time when you should be repotting, the buds should be swelling, so if you start pruning at this time, you are just removing potential energy from the tree, which is just very wasteful …although I do normally see this mistake being done at the same time as ‘repotting at the wrong time’ so it is doubly bad.

Not Raking Out The Roots Is A Mistake

If you are going to get the tree out of the pot and prune some roots, you should really rake the roots out first.

There are only a few rare occasions when this doesn’t need to happen, but in the majority of cases you need to see what you actually have.

If watch any videos where the tree is root bound, you will understand why it’s so important to rake everything out. It can be very hard to tell what is actually going on and the only way to find out is to rake everything and untangle the mess.

It is then at this point you can decide how much you want to prune and you can just access how well your root ball is developing. You can see if there is one root plane and is any areas are stronger or weaker.

If you are not doing this, then you are just blindly working the roots which is a pretty stupid thing to do.

(You can read more about – How To Repot A Bonsai Tree)

Removing Too Many Roots Can Be A Huge Mistake

When you repot you will have to remove some roots, but it is very easy to get carried away with this.

This is probably not helped by the many youtube videos (that I make) that show some serious root removal.

This can be possible and totally safe at times, as my videos will certainly show as you will see the tree growing strongly after …but it still always a risk.

You need to understand the species you are working with and know how much work they can handle, as well as know how healthy your tree is and get your timing right.

If you are not sure about any of these, then you should be cautious. It is better to leave slightly more roots and wait until next year to deal with them again …rather than removing too much and killing the tree.

Your goal is to remove what you can, while balancing the health of the tree. This can be a fine line at times, so like I said, if you are not sure, be cautious.

Washing The Roots Is A Mistake

Washing the roots is an interesting subject. There is a time and a place for it, but I think it is over used and misunderstood.

The soil and roots usually have a bit of a beneficial partnership going on. There are organisms in the soil that help the roots and vice versa. Everyone is healthy and happy and you can really see this in action with pine trees where you will see a white fungus in the soil called mycelium.

Washing the roots can flush all of this good mircobiome away, which is not ideal. I guess it can be compared to how an antibiotic can flush away all your good stomach bacteria.

Really you only want to be washing the roots when it is extremely necessary and that is really only going to be when you have a tree that is in terrible soil.

Nursery soil can be bad, but it’s usually fairly loose and you can get it off to the point where you can see what you have, without washing. I think the real problem is with trees form the ground in very sticky clay like soil. Often this soil is so bad the only option is to wash it.

I would argue that it isn’t really going to have much of a microbiome, so you are not missing out on much by washing this off.

Once your tree is in good bonsai soil, you shouldn’t need to wash the roots, the soil should be easily removed, even if it is broken down and not in a bad way.       

Removing Old Soil Can Be Good or Bad

This mistake is kind of linked to the above point about washing the roots.

As I mentioned above, soil has a microbiome that is beneficial for the tree, so removing this can be bad.

Usually this is removed by washing the roots, which is not great, but as I mentioned …some soil is terrible and needs to be washed off. If you are removing sticky wet clay like soil, this is fine. This is probably causing the tree more problems that good so it is sensible to remove it.

However, once your tree is in bonsai soil, you shouldn’t be so quick to remove all of the soil.

This may sound contradictory to what I said above and I do in my videos …which is rake all the soil out.  It is true, I do rake all the soil out and remove it … but that is temporary. I do this to see what I am working with and then if you look closely you will always see me take at least a handful of the soil I just removed and place it back in the pot along with some new soil.

Doing this, along with not washing the roots means I have still kept a lot of the healthy mircobiome after repotting. I have of course reduced its levels and the majority of the pot is new soil …but there are always some old particles in there and any helpful organisms can quickly spread and repopulate the whole pot and keep things healthy.

Not Trying To Develop A Single Root Plane Is A Mistake

When you are in the early stages of developing a bonsai tree you want to try and get its roots under control which means trying to develop only one root plane.

As I have already mentioned above …removing too many roots at once can be a mistake, so trying to develop a single root plane can be a bit of a balancing act.

This is something that might take a few repottings to sort out, but you should always be trying to progress your roots as much as you can every time you have the tree out of the pot, especially in the early days.  

I see too many people not really worried about this, which is a mistake. They have kind of accepted that their tree hasn’t got a flat root plane and are not making any effort to correct it. I think it is fine to take your time, but you actually have to do something.

Just ignoring the problem is not going to get you fantastic roots.  

Not Using The Right Size Pot Is A Mistake

The Pot size of your bonsai is pretty important and while there is no right or wrong pot size, there are some mistakes you can still make.

You want to use a pot that is in line with your goals and is also good for the trees health. This means if you are trying to grow your tree out, you should use a bigger pot. The classic mistake is trying to develop a tree while it is in a bonsai pot

I know this is a mistake I make all the time. I know it’s not ideal, but I have not got the space … and I know it very suboptimal for my trees progress.

You can also cause problems if you go in the other direction and use a pot that is too small, as this will just not give the tree the space it needs to stay healthy.

As with most things in bonsai, it is all about balance.

(You can read more about – What Is The Right Size Pot For Your Bonsai?)

Not Working the Soil Into The Roots Is A Mistake 

Working the soil into the pot is extremely boring, but vital!

This is when you add soil the soil to your pot, then take something like a chop stick and poke it into the soil. You then wiggle this about and you will see the soil sort of gets sucked down, like you are creating some sort of vortex.

You will notice when you do this that the level of the soil sinks and you need to add more soil.

Basically what is happening here is that you are jiggling things around and allowing the soil particles to move down and actually fill any gaps and it gets rid of any air pockets.

This is especially important around your roots, where any sort of pocket of space would be very detrimental to the tree. This area would easily dry out and the tree would struggle to grow in these gaps.

It is so important that you work the soil into the pot. I don’t really show this in my videos, but I do spend a lot of time on this as it really can kill your tree if you do not work it into the soil correctly.

Doing this also helps the tree be more stable in the pot, it can feel like the tree is really gripping the soil afterwards, which is of course very ideal, especially if you are lazy like me and do not wire your trees into the pot.

Not Having Good Aftercare Is A Mistake

Repotting the tree is only half the battle, once you have done your work you need to help the tree recover and get back to full health.

Not giving your tree good aftercare is going to cause it to struggle and it may not be able to bounce back to health.

Aftercare is not hard, you just really need to pay extra attention to the tree and make sure it is happy. You may need to shelter it for a while and you will have to water it differently until the roots have healed.

If you can look after you tree correctly it will bounce back with no problems.

(You can read more about – Repotting Aftercare Advice For Your Bonsai)

Conclusion

So as you can see, there are a lot of mistakes you can make when repotting a tree. It isn’t a particularly hard process, but there are plenty of little mistakes that can trip you up and they will be very costly as they can cause your tree to die.

Hopefully now you will be able to avoid all of these issues and have a much higher rate of success when it comes to repotting and have much healthier trees because of this.

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