What Is The White Crust On My Bonsai Pots? (is it dangerous)

White Crust On Bonsai Pots

So recently, I found that my Chinese Elm bonsai had started to develop a thin white crust on the lip of its pot. While I initially thought this might be the white powder or spots synonymous with fungal infections, on closer inspection, this wasn’t the case. So what was the white crust on my bonsai pot? 

Thin or thick white crusts on the inside lip, outside lip, or wider body of a bonsai pot are caused by a build-up of calcium carbonate particles. These calcium particles are common in tap water, so if you excessively water your bonsai tree with tap water, this will build up over time. 

To prevent this, use rainwater or filtered water with lower calcium levels. 

So is a build-up of the white crust caused by calcium deposits dangerous? And can a white crust on bonsai pots be caused by anything else? Keep reading to find out more!

White crust on bonsai pot

To get to the bottom of exactly why my bonsai pot had developed a white crust, I got in touch with my local botanical gardens, visited my local bonsai tree expert, and even got in touch with 20 plant paladin readers asking them why this was the case. 

All to ensure you had the most detailed post on white crusts on bonsai pots. 

To summarize: 

  • Having a bonsai tree pot that has a white crust on it is typically nothing to worry about. 
  • The leading cause is excessive calcium or magnesium in your pot. 
  • This most commonly happens when the water molecules hydrogen and oxygen are absorbed or evaporated from the potting soil, leaving trace amounts of magnesium and calcium. 
  • These trace amounts build up until thin white spots/crusts appear on your bonsai pot. 
  • White crusts are usually much more common in areas with hard water. 
  • To prevent this, consider watering with filtered or rainwater
  • To remove the crust directly from an existing pot, wash with warm filtered water and use a tooth or bonsai brush to rub through. 
  • White crusts on a bonsai pot are typically not dangerous; however, it may be a fungal infection if the white spots persist and grow on the leaves, trunk, and potting soil. 
  • In this scenario, use a suitable fungicide to protect your tree. 

This is a lot of information, so let’s discuss this further!

What causes the white crust on bonsai posts? 

So I do not doubt that you are looking for answers to a white crust on your bonsai pot because you have recently seen one develop. 

Fret not, as this is something that I, too, did. 

The good news – it’s not something you should worry about!

Water is The leading cause of the white crust on bonsai pots. 

More specifically, tap water. 

And more specifically then, tap water in challenging water areas

You see, most of us will water our bonsai trees about two to three times weekly. 

Tap water, being convenient, is usually a go-to for most of us. 

Tap water contains trace amounts of minerals like magnesium and calcium (due to the copper pipes and water treatment process).  

When the water gets absorbed or evaporated by your bonsai tree, it leaves behind calcium and magnesium, which usually cling to the most accessible surface they can – your pot.

Over time, these trace amounts start to build up, and it’s not uncommon to see white crust develop after a year or two of keeping your bonsai tree. 

Do any other minerals cause a white crust on your bonsai pot? 

In almost all scenarios, it is magnesium and calcium minerals that are the cause of the white crust on bonsai pots. Most other minerals are light enough o be absorbed or evaporate away with the water. 

How to remove the white crust on a bonsai pot?

So now we know what the white crust on your bonsai pot is. Naturally, the next question you want to be answered is how to eliminate it. 

The good news is that this is not difficult and can be undertaken in quite a few different ways. 

These include: 

  • A toothbrush/bonsai brush and water
  • Using vinegar
  • Descaler
  • Scraping off by hand ( for antique pots)

Let’s explore these in more detail: 

Using a toothbrush

So the first method is the easiest, cheapest, and for 90% of you, will get rid of the problem. 

This, then, is super easy! 

Get a toothbrush with either plastic or metal bristles. 

Then gently remove your bonsai tree from its pot. 

Fill a kettle or pot with hot water (ideally water that has been filtered or rainwater) and submerge your empty pot. 

Then using the toothbrush scrub the crust until it disappears. 

Leave to dry overnight and inspect your results in the morning. 

Repeat the process if you still see crust bits on your pot. 

Now if you have a lot of crust, you may need to repeat this a few times. 

Add a touch of liquid soap to your hot water solution, which should help loosen the tough crust. 

Typically, you will undertake them when repotting your bonsai tree – just because it’s convenient. 

After all, removing your bonsai tree from its pot every six months could risk damaging your tree’s roots. I then aim to give my pot a good scrub, so once every two to 3 years or the same amount of time you repot your bonsai. 

Using vinegar

If the toothbrush method doesn’t work, we may need to get more acidic. 

As many of you know, vinegar is a fantastic cleaning agent and is especially useful for removing tough crusts. 

The method then will be similar to the one laid out above. 

Remove the bonsai tree from the pot and wash thoroughly. 

Then place either regular household distilled vinegar or 100% vinegar in a bucket and place the bonsai pot inside. 

You can scrub off the crust with a sponge, brush, or metal scorer. 

To speed up this process, you can heat the vinegar slightly, which should help remove any difficult-to-remove calcium crusts. 

Alternatively, leave your bonsai pot in vinegar overnight before removing the crust. 

This will give the vinegar more time to work; surprisingly, you won’t need a brush to remove the crusty residue. 

The only downside to this is that vinegar can cause a fair bit of damage to organic material like your bonsai tree. 

This means that if you plan on using the same pot again, it is best to let it soak in filtered water or rainwater before plating your tree again. 

This is to ensure that it doesn’t change the PH level of your bonsai trees soi, which can impact the health of your trees. 


The two above methods will be the best, but you may consider using a descaler in extreme cases. 

Descaleers are typically used in kettles, pots, coffee machines, and even dishwashers to remove limescale and hard calcium deposits in these devices. 

Now descalers contain potent chemicals that will strip out the calcium from your pot. 

However, this should only ever be treated as a last resort. 

The main reason is chemicals used in descaler tablets tend to get absorbed into the pot and can have a long-term impact on your tree’s health. 

As such, I can’t recommend them for you to use – effective as they may be. 

If you want to use these at your own risk – don’t say I didn’t warn you. 

Scraping off by hand

While removing the scale by hand with a small pick or brush will be incredibly time-consuming and tiring, without any water may be the best option for some. 

I then recommend this if you have an old antique bonsai pot

This is because even light solutions like vinegar or water can damage 100 to 200-year-old bonsai pots, so hand-removing the calcium build-up will be your best bet.

I like to use a dry microfibre cloth and small makeup or bonsai brush to do this. 

Gently rub until you have removed the calcium. 

You should dampen the cloth slightly for the challenging crust areas but keep the cloth tight against your ancient pot, which may crack very easily. 

Take it to a professional 

Finally, if you feel nervous about cleaning your bonsai pot, especially if it is an antique, consider meeting with a professional. 

Most independent garden centers will be happy to clean your pot for you or even teach you the best way possible to clean your pot. 

What is the best method to remove white crust from a bonsai pot?

The best method to remove white drust from a bonsai pot is to place your bonsai pot in warm water and scrub thoroughly with a toothbrush. Apply one teaspoon of liquid soap to help further soften the calcium crust on your pot. 

To help summarize the best method to remove white crust from a bonsai pot, I’ve created a comparison table below: 


Difficulty (out of ten)

Potential problems

Brush, water, and soap


Ensuring your pot is completely dry before using it will allow you to spot any calcium deposits you may have missed.

Vinegar and water


Potting your bonsai directly back can change the PH level of your bonsai soil



Easy to use, but chemicals can be too intense for older antique pots.



It can be hard to get into all the cracks and crevasses.

How to prevent white crust on bonsai pots? 

Now while you can easily remove the white crust from your bonsai pot, prevention is always better than a cure, so how can you prevent your bonsai pot from developing a crust in the first place? 

Luckily, you can follow a few quick solutions to ensure you don’t have excessive white build-up in your bonsai pots. 

First, stop watering your bonsai trees with tap water. 

Calcium and magnesium deposits are the main reason for the excess white crust on a bonsai pot, so using filtered water or rainwater will help prevent this. 

Next up, I’d suggest not overwatering your bonsai tree. 

During the summer, it can be very tempting to water your bonsai a few times per day but ensure you only water when the topsoil is dry, typically once to twice per week for most bonsai species. 

Finally, consider changing the potting soil for your bonsai tree. 

Over time, soil begins to break down and could be more efficient at allowing nutrients and moisture to flow. 

If, then, you are finding you have excessive calcium build-up in your pot, consider changing your potting soil and bonsai pot. 

Is white crust on a bonsai pot dangerous? 

The white crust on your bonsai pot is not dangerous to your bonsai tree aside from being aesthetically unpleasing. 

While excessive calcium or magnesium crust on your bonsai pot might cause a slight change in the PH level of your soil, this is no different than using a solid fertilizer for a prolonged period. 

As such, if you were to change and repot your bonsai tree during the recommended timescale ( once every two to five years), then there would be no negative impact on the health of your bonsai. 

Think of it like this, me and you, our pets, and all our plants drink tap water daily; as such, the harm of using tap water and the calcium build-up is negligible. 

Which pots are most affected by white crust? 

Terracotta bonsai pots are the most likely pots to develop a white crust. This is because terracotta can be very porous, allowing calcium to be absorbed over time. Older ancient bonsai pots that have aged over time will also be more likely to be affected by a white crust. 

Most plastic pots, however, do not get a white crust build-up. 

How to look after your bonsai pots? 

I would follow a few key attributes to look after your bonsai pot. 

These include: 

  1. Ensure your pot is the right size for your tree – pots too small may become damaged over time. 
  2. Aim to clean your pot – Ideally, keep the outside of your bonsai pot clean by whipping it down with a damp cloth every few months; when repotting your bonsai, wash thoroughly. 
  3. Do not pot stuff – avoid placing your pots inside each other – this can cause the pots to expand and crack. 
  4. Keep your pots safe – avoid placing pots near pets or spaces they can be easily damaged, especially ancient bonsai pots. 
  5. Repot at the right time – it’s important to remember that most bonsai pots are only suitable for a short period in your bonsai trees life. Try to keep your tree in a different pot for a short time. 

White stuff on bonsai soil?

So now we have touched using a white crust on your bonsai pot; what happens if you notice a white substance on your bonsai soil? 

Mildew fungus is the most common cause of a white fluffy substance on your bonsai trees soil. Fungicide should be undertaken to remove to prevent your trunk from becoming squish and the potting solid from becoming ineffective. 

Survey results on what is the white crust on my bonsai pots?

So finally, I didn’t want to give my insight into the white crust on a bonsai pot but provide additional information. 

As such, I asked 20 plant paladin readers the same. 

Here are the results: 

What Is The White Crust On My Bonsai Pots - survey results

Fehed Nicass

Fehed Nicass has been passionate about all things bonsai and botany focused for the past 3 years. What started out as a hobby has developed as a passion and he is now on a mission to teach and learn.

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