What Is The Right Size Pot For Your Bonsai?

Getting the right size pot for your bonsai is pretty important. You want a pot that is the right size so that your tree can remain healthy and also look good.

If your pot is too small the tree will struggle to stay healthy, and if it is too large …well this can be okay at times, but it is still not always ideal as it doesn’t look great.

I will go through some things you can evaluate to make sure the pot you have selected is the perfect size for your tree. 

The Trees Health Is Always The Most Important Aspect

When it comes to anything involving the roots, the health of the tree should always come first.

While you may have a certain pot size in mind, really it is the tree who will decide if it is the right size or not.

You will need to make sure that the pot size you select will keep the tree healthy … if your tree dies, then that’s not exactly great, is it!  

The Roots Need To Fit Into The Pot

It sounds self explanatory, but you want to make sure that the roots can fit inside the pot.

Of course you can do some pruning to make sure they fit, but this is where you need to balance the health of the tree. You need to know what the tree can handle, which will come down to its species and its current health.

Once you have pruned everything and you are ready to put it back in the pot, this is where you now need to make sure it will fit properly. At this point you will have probably pruned it as much as it needs, so if it doesn’t fit now …you need to be very careful. You might be able to get away with a little more pruning but if you have reached the limit, you need to be honest with yourself and find a larger pot.

Pruning the roots to make them fit in a smaller usually ends badly and is something I would try and avoid.

(You can read more about – Should You Use A Smaller Or Larger Pot When Repotting A Bonsai?)

The Pot Needs To Be Wide Enough

One of the considerations for size is the width of the pot. This can be in any direction, but basically you want the roots to be able to fit in and not be touching the edge of the pot.

When the roots grow they will reach the inner wall of the pot and then as they can’t keep growing out they will be forced to change angle and start growing downward.

It is important to realise this before hand, as you do not want your root spread to grow in a way where it suddenly bends downward.

Having enough space around the edge is going to avoid this. The tree will still grow and hit the edge and bend down, but your main root spread isn’t going to be effected. The next time you repot, you can prune the roots back to just before the point where it changes angle.

The Pot Needs To Be Deep Enough

The pot should also be deep enough to contain the root ball; ideally you want some room below your tree, so that roots can grow downward.

If the base of your tree is touching the bottom of the pot, then you have two problems. Firstly, there is no room for the roots to grow downward as I just mentioned and secondly, you will probably find that your trunk flare is now below the rim of the pot and it will get buried by soil.

This is going to result in the roots having to grow upwards, since they can’t exactly go down, which is going to totally ruin your roots going forward and you will have to spend a number of years correcting that. It also means your root flare is hidden, while that is not really a problem, it does mean you can’t look at it and enjoy it.   

Sometimes you will see the tree planted very high, as if the pot has been filled with soil, then the tree is placed on top, as if it is level with the rim. So long as the roots are covered with soil this can be okay, as basically the entirety of the pot is below the tree is now “empty” space and the tree can grow into this.  

Normally you see this happen with very shallow pots, where space really is a premium, but you could do it with any pot.    

There Needs To Be Room For The Tree To Grow

Basically if you can get the right width and depth for your pot, then you are going to have enough space for the tree to grow.

Your tree is going to grow throughout the season and it is going to fill the pot with roots. If you are using a small pot, this can happen pretty quickly. You need to understand how your tree grows and guestimate if the pot size is going to be okay for how fast it might grow.

Some trees may be extremely aggressive and while the pot size might look okay, it might not actually be enough. You also need to consider what stage of development your tree is at. Sometimes using a pot that the tree is going to quickly fill up can be adventitious. Once it is full, it is going to struggle to grow, as it has no more room. This will slow down the overall growth of the tree, which is what you sometimes want.

This is a bit of a balancing act, as you don’t want your tree to struggle too much, but you might not also want to be able to grow freely and grow like crazy. Hopefully you have had the tree for a number of years and have a good feel for how it grows, this will help you work out how to balance this.

A lot of bonsai is learned through experience and you will start to get a feel for what pot size is right for the tree after seeing how it reacts over a couple of years.

General Aesthetics Guide To Pot Size

I’ve already talked a lot about what size is going to be right for your tree and everything I’ve mentioned if pretty much common sense. However, if you look to Japan you can see some very loose guidelines on what pot size is right.

I wouldn’t call them rules, probably more “considerations” the information above is more important as it will make sure your tree actually fits into the pot and more importantly stays healthy, but I will go through some of the general rules you might hear as they can be very aesthetically pleasing if you can follow them, or at least get close to them.

It is suggested that the width of your bonsai pot should be about 2/3rds of the height of tree. This means if your bonsai is 30cm tall … then your pot should be 20cm wide.

If you have short stumpy tree … so one that is wider than it is tall, such as any sumo style tree, then you need to measure the width of the trees canopy instead of the height. You then want the pot to be 2/3rds of this length. So if your tree is 30cm wide, you want the pot to be 20cm wide.

As for the depth of the pot, it is usually suggested that that this should match the widest part of the trunk. Usually when you look at the trunk it will get wider and start to spread out into the roots. You need to look at the widest section and however wide this is, is how deep your pot should be. 

However, this will really depend on the thickness of your trunk and some styles of tree may be much thicker than the other, so it’s not always a perfect guideline to follow.

You will also hear people say that the width of pot should just be a little smaller than widest part of tree, which is obviously a little different than what I just said above, and shows how all of this really is just a guideline and not a set of rules.

You really need to take each tree and pot on its individual merit and see how they work together. If it looks good to you, and the tree can be healthy in the pot …then that’s all matters.

You Should Also Consider Your Local Environment When Thinking About Pot Size

An often overlooked area of pot size selction is your local climate. Your tree is going to be growing in this pot and while you may be watering it every day, the climate is going to affect things.

If you live somewhere very hot, or with a lack of humidity, then you need to take this into consideration. It might be sensible to use a slightly larger pot than you want to, just so you have slightly more soil and so that the tree is less likely to dry out, or just generally struggle.

The opposite could also be true if you live in a very wet climate. You want your trees to maybe be a slightly tighter fit, just so that there is not a lot of free soil that is able to sit waterlogged. However, in this situation I wouldn’t worry about this as much, as you can shelter the tree, and as the roots grow, the amount of free space will reduce, meaning it’s not really a problem for long.    

You need To Think About Your Soil Too

While I am talking about pot size here I think it would foolish to not mention soil, since that is what you are going to be putting in the pot.

You will want to use good bonsai soil, but you need to know how your soil acts in your climate. As I just mentioned above, using a larger pot might give you more soil, meaning the pot doesn’t dry out as fast …but that isn’t the only way to do things, you could just use slightly different soil that will hold the water for longer, meaning you don’t need a bigger pot.

Ideally you want some sort of combination of the two, you want a pot that you know is going to be the right size and you want soil that you know will work well in your climate.

(You can read more about – A General Guide To Bonsai Soil)

Conclusion

I know it’s a lot to juggle and process, but over time you will get a feel for things and if you follow the general advice above you will end up with a good size pot for your bonsai.

Over the years you will learn how your climate works, how your trees grow and how your soil interacts with everything. After a few seasons you will get a feel for what pot sizes are going to work well or not.

If you are in doubt now, always be cautious and use a slightly bigger pot, trees usually enjoy a bit more space and can usually survive in these. If you go to small, things can get a little risky, so that’s the type of lesson you want to try and avoid.