Charcoal for Terrariums – Is It Necessary?

Charcoal for terrariums comes in many forms, it’s hard to know what’s best to use.

Which is a problem when using the wrong charcoal in your terrarium has been shown to have potential negative effects.

Not to mention all those voices out there contesting whether charcoal has any benefits in terrariums at all (even the supposed “best kind”).

So, is it even worth it?

In this article we’re going to discuss how charcoal can be beneficial to a terrarium, which types are suitable, and ultimately whether you should be using it in your terrariums.

Let’s get stuck in.

The Potential Benefits of Charcoal in Terrariums

Unlike in general gardening, charcoal is not used as a soil additive in terrariums. Instead, almost everyone online seems to recommend a complete layer of charcoal near the bottom. 

It’s key function? Filtration.

Because after all, terrariums are ecosystems, and every ecosystem has an unpleasant side that needs clearing out.

Leaves fall off, plants die and eventually that organic material will begin to degrade and break down.

Now, it’s important to mention that these things are entirely normal

None of these things spell the end of your terrarium, but left unattended they pose some potential problems.

  1. Decaying organic material releases unpleasant gasses and toxins that can be harmful to your plants (and your nostrils).
  2. Increased chances of harmful rot in your terrarium.
  3. Potential overgrowth of unwanted moulds and mildew.

This is where charcoal (allegedly) helps. 

From horticultural charcoal and aquarium filter pellets, to chunky BBQ charcoal – I’ve seen all kinds being recommended online.

Which is weird because there’s only one kind that’s able to truly bind impurities, and that’s “activated charcoal”.

What is Activated Charcoal?

Otherwise known as “activated carbon”, activated charcoal is a type of charcoal that’s been treated at very high temperatures.

“A type of charcoal that’s processed to make it more porous. This porous texture is what distinguishes it from other types of charcoals, including the type used for barbecuing.”


This distinction is important.

After all, it’s the increased porosity of activated carbon that allows it to bind impurities.

Activated carbon comes in a variety of forms (powders, pellets and tubes) but the function is the same.

Activated charcoal for terrariums
These charcoal “tubes” can be good in false bottoms (probably best broken up a little).

So, if you’re adding charcoal to a terrarium for it’s toxin binding abilities, you must buy activated charcoal!

Sounds Great, Would We Not Use It Then?

Let’s start with the facts. Activated charcoal is very effective at binding a wide range of toxins and impurities.

This much is not up for debate. 

What’s not so clear is the long term effectiveness of the material in a terrarium, and whether a terrarium needs such a filter at all.

Activated Charcoal Doesn’t Remain “Activated” Forever

If we imagine activated charcoal as a sponge – soaking up all those toxins and gasses – like any other sponge, eventually it will become saturated. 

Remember, activated charcoal does not have an infinite buffering capacity

Where activated charcoal is used in aquarium filters, it’s often recommended that they are changed every 2-4 weeks.

Which is a little worrying, considering we want our terrariums to last years…

But there are things to consider here before we assume our plant terrariums are going to be the same.

  1. Aquarium filters typically contain a much smaller amount of activated carbon than a full terrarium layer would.
  2. In an aquarium, the volume of water pumped through the carbon on a monthly basis is significantly more than will pass through a terrarium layer.
  3. Aquariums generally house lots of marine animals (otherwise it’s just a tank of water?) and they’re going to produce significantly more waste than terrarium plants alone.

I’ve not been able to find any legitimate sources to suggest how long a layer of charcoal in a terrarium might last.

However, working on the basis of an aquarium filter lasting an entire month, and the demands of a terrarium charcoal layer being theoretically much lower, I would imagine it would last longer.

Just don’t quote me on that..

Is Charcoal Filtration Needed In an Open Terrarium?

If the main purpose of activated charcoal is to trap gas and odours. They shouldn’t be a problem in an open terrarium right?

It’s not a closed system, and gases should just escape into the atmosphere.

Well, binding smelly gases is just one function of a charcoal filter. An important one, but a charcoal layer should still be useful at filtering any water contaminants.

It may still be useful at absorbing potential plant pathogens, heavy metals or toxic substances.

So, I’d argue it’s still useful in an open terrarium – just less effective/necessary.

Where to Buy Activated Charcoal for Terrariums

So, are you convinced of the power of activated charcoal to cleanse your terrarium?

If so, you’ve still got to find the right stuff.

These are suitable charcoal sources that will actually bind impurities and filter your terrarium.

  1. Aquarium filter charcoal is actually used in (what is arguably) a water-based terrarium. It’s made for purpose and it’s what I tend to use. Here’s a tub on Amazon for a bargain price.  
  2. So-calledactivated charcoal for terrariums” like this one. You still have to read the label (it’s not like this stuff is “certified for terrariums”) but it’s a good place to start in your search.
This is what I’ve been using but I don’t think the brand is important. Made for large aquarium and pond filters.

Unsuitable Charcoal for Terrariums

  1. BBQ and fire pits – People often ask “can I use BBQ charcoal for terrariums?” But the Royal Horticultural Society don’t recommend using barbeque charcoal because it often contains contaminants that can be harmful to plants. 
  2. Horticultural charcoal – I’ve seen this recommended in a bunch of places online. It has many great qualities for general plant potting, but horticultural charcoal is not activated charcoal. No binding = no benefit for terrariums.

So, Is Charcoal Necessary for Terrariums?

Well, the short answer is, probably not.

Not 100% necessary, but almost certainly helpful

A terrarium can and will function without a charcoal layer. The real question is whether a charcoal layer has a positive long-term effect on a terrariums health.

Unfortunately, there’s no concrete evidence to show how effective charcoal is at filtering out unwanted impurities from a terrarium.

In theory, it makes sense – and there’s anecdotal evidence from experienced terrarium builders to suggest it’s a helpful addition – but like many aspects of terrarium building, it’s down to personal choice/trial and error.

From what I can find, there’s no real downside to having an activated charcoal layer.

If you’re building terrariums using the false bottom approach, charcoal is still useful as a drainage element. So if it’s sat between your drainage rocks and your substrate then it won’t be interfering with your plants much anyway.

If you’re not keen on adding charcoal, try adding more terrarium moss! Moss naturally filters water anyway, and can even remove things like arsenic.

What Do You Think?

I’m really interest to hear if you use charcoal in your terrariums.

Have you found one type to be superior to another?

Or do you forgo charcoal entirely and still have a thriving terrarium?

Let us know in the comments below!

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1 thought on “Charcoal for Terrariums – Is It Necessary?”

  1. Tilde Andreasen

    Bought this item for my moss terrarium and works great! Prevents any odors and helps with the overall system of the terrarium The charcoal does have a very strong distinct smell at first, but it clears up in a few days. The size is just right for what I need. Not tiny dusty chips, but just the right size

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