Activated Charcoal for Terrariums: Is It (Really) Necessary?

Charcoal comes in many forms, and it can produce some very different results in terrariums.

You’d be forgiven for thinking it’s all just burnt wood. Alas, there’s actually a lot more to it, and it’s worth checking how effective your choice of charcoal is and whether it’s safe to use.

Plus, the concept of “activated charcoal” raises some new questions.

Is the modern “purifying” wonder material all it’s cracked up to be? 

We’re going to answer that exact question as we explore how beneficial charcoal can be to a terrarium and which types you should be using.

So, is charcoal the new black? Let’s find out.

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The Potential Benefits of Charcoal in Terrariums

Charcoal is already commonly used as a soil additive in the wider gardening world. 

It’s said to increase water and nutrient retention, improve soil structure, and even support healthy microbial life. The list of benefits goes on, and all of these benefits transfer nicely to terrariums too.

But these aren’t the reasons that charcoal is so popular in terrariums.

Instead, charcoal is used for its powerful filtration properties

That’s why you’ll often see people online recommending a complete layer of charcoal at the bottom of a terrarium. To “clean” any water that passes through it. 

We like to scatter ours on top of the mesh barrier layer between the drainage and substrate.

Now, charcoal’s purifying abilities are undeniable (that’s why it’s used in everything from skincare to medicines), but how that plays out in a sealed terrarium system is a little harder to quantify. More on this later.

Why Does a Terrarium Need Purifying?

Terrariums are ecosystems like any other.

Leaves fall, and plants perish, 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 for too long, they can 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 mold and mildew.
terrarium tools tweezers removing a deceased leaf
Removing these things works too!

This is where charcoal comes in. 

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

But there’s one that seems to be used universally, and that’s “activated charcoal.”

Why is Activated Charcoal Superior in Terrariums?

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

Healthline defines activated charcoal as “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 more effectively. Studies have suggested that the “activating” process can increase carbon’s binding capacities up to 10x.

“Thus, a 50-g dose of activated charcoal has an adsorptive surface area equivalent to about seven football fields! “Superactivated” charcoals may have a surface area of 2,800-3,500 m2/g”

Activated Charcoal for Acute Poisoning: One Toxicologist’s Journey – Kent R. Olson

Whereas non-activated charcoal may have a surface area of just 400-800 m2/g.

So, when we consider the function of a charcoal layer in a terrarium, activated charcoal would seem to be far more effective.

Activated carbon itself comes in a variety of forms – including powders, pellets, and tubes – but the function is the same. The type you choose is probably going to determine how you use it (e.g., mixed in or separated).

Counterpoints to Using Charcoal in Terrariums

If we imagine activated charcoal as a sponge that’s 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…

2. Open Terrariums Don’t Really Need Charcoal Filtration

If the main purpose of activated charcoal is to trap gas and odors.

They shouldn’t be a problem in an open air 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 for filtering any water contaminants. It may still be useful for 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 Charcoal Suitable for Terrariums

There are tonnes of charcoal options online.

You can find it in a wide variety of different sizes and granularities. So, whether you’re looking to create a full layer of activated charcoal chunks or mix it in with your terrarium substrate, you’ll be able to find something suitable.

Alternatively, the tough activated charcoal tubes or pellets can function well as the drainage material in a false bottom. 

I’ve tried using activated charcoal in all of these ways before, but I prefer the clean look of a separate layer.

We sell fine-grade, coconut-based activated charcoal. So it’s super versatile and eco-friendly! 👇

coconut-based activated charcoal for terrariums
👉 Shop our activated charcoal for terrariums!

Unsuitable Forms of Charcoal for Terrariums

We’ve discussed which kinds of charcoal are best for terrariums, but there are some forms that are simply not suitable. Mostly because they can bring in extra unwanted substances. 

  1. BBQ charcoal briquettes – The Royal Horticultural Society doesn’t recommend using charcoal briquettes with plants because “Modern barbeque briquettes can contain additives or contaminants (coal, tars, resins, and other chemicals) that are not suitable for addition to the soil.”
  2. Used charcoal from stoves or fire pits – Additionally, the RHS doesn’t recommend used charcoal as “it may be contaminated with harmful chemicals or microplastics. Also, application of any incompletely burned/charred materials can be toxic and/or decompose in the soil using up nitrogen.”
horticultural charcoal chunks
While BBQ and used charcoal chunks won’t be suitable, if you can’t get your hands on activated charcoal, horticultural charcoal is an option that would work. It doesn’t have the same filtration potential, but it’s better than nothing.

So, Is Terrarium Charcoal Necessary?

Well, the short answer? It’s not 100% necessary, but almost certainly helpful.

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

Unfortunately, there’s no concrete evidence on that front.

In theory, it makes complete sense, and there’s plenty of 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 charcoal in your terrarium.

It’s going to bring some level of purification. And if you have it mixed in with your terrarium substrate or use it as a drainage layer, it’s going to bring the usual benefits too. What have you got to lose?

Either way, it’s an easy addition to your terrarium materials and worth exploring.

What Do You Think?

I’m really interested 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!

20 thoughts on “Activated Charcoal for Terrariums: Is It (Really) 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

  2. While activated carbon is engineered to have the most surface area in order to “bind” the most passing contaminants and will generally yield better, more dependable results, natural lump wood charcoal still “binds” contaminants and WILL perform the same function as Activated (granted, less effectively) – especially when broken and pulverized into varying sizes from chunky to nearly dust. It’s commonly used in successful terrariums and vivariums all over the world. Activated charcoal is a better, cleaner, more expensive alternative. Lump wood charcoal is fine if untreated, natural, etc. Never use charcoal briquets, period.

    1. Thanks so much for your insightful comment. I honestly hadn’t been able to find evidence to back up the idea that horticultural charcoal binds toxins (despite it being a commonly held belief). After reading your comment I have been able to find studies that suggests it’s about 1/4 the efficacy of activated charcoal. I’ll update the article to reflect that. Cheers!

    1. People tend to run with 5-10% of the overall mix, but I’d imagine a small handful would be enough for a terrarium of that size 😀

  3. Hey, I’m currently setting up a 12x12x12” terrarium/vivarium that will eventually hold isopods, millipedes, & darkling beetles. Some of the isopods are in already, along with two plants (waiting for more to arrive). I didn’t know to put a bottom layer of activated charcoal in, so the substrate is sterilised organic compost, peat, coconut coir, worm castings, & a little sand. There’s no way I could get – layer under the substrate now — should I just mix it through the substrate? Or should I add moss instead? Or both?? Thanks!

  4. Activated charcoal without regeneration is basically inert in about a month. I think the charcoal layer in a terrarium is something like a superstition.

  5. I am just starting my first closed terrarium and already have a very fine activated charcoal. Should this be cleaned before use. Grateful for any help. Thanks.

  6. Thanks for your article. Just starting my first terrarium. I’ve kept marine tanks for years and have always used carbon. I’d say that carbon in a terrarium should last much much longer than that of a marine tank. In a marine tank, there are lots of biological chemicals thrown into the tank from spawning invertebrates including corals and anemones. Lots of chemical warfare (toxins) excreted from various corals so carbon is essential. I’d say that if the plants aren’t excreting large amounts of toxins, the carbon should last for a year at a minimum; especially the larger, more porous types. The pores can hold onto a lot of junk and I find it hard to believe they’d be overwhelmed by the plants, water and decaying matter unless in the case of overwatering.

    1. Hi Scott, thanks so much for your insightful comment (we’re relying on anecdotal data here really, so your input is really valuable). A year or more of buffering capacity would certainly make it worth considering.

  7. Thank you for this article! I am just starting with closed terrariums, and found terrarium soil with charcoal, and got a separate bag of horticultural charcoal as well. And I was wondering about what and why. Your article really helped me realize I could do either. And how to adjust the one terrarium where I left it out. And i did not know about activated charcoal and now I do. I earned a lot from this, Thank you!

  8. Can you use dirt from outside, my son wants to try and make one with all supplies from our yard, is that possible? Help😩

      1. I’m just starting out myself, so I don’t have any first hand experience, but I’m getting materials together after watching a video follow up on this kind of “experiment”. The guy had made one entirely with found materials, including the container (an empty food jar) and had said himself that he usually would use activated carcoal, but skipped it for this sinceit’s not something most folks could find for free.

        The original video was from five years ago; the flow up was posted six months ago. One of the types of moss he’d added was eventually lost, but other things grew that he hadn’t intended (since it was all found outside) and there had supposedly been minimal maintenance- just trimming some things back and cleaning the glass.

        Granted, they guy has tons more experience, so maybe not the results someone else might get (like some random dunce tossing second-hand “knowledge” in a comment section >_>) but it might be encouragement someone who doesn’t have activated charcoal to still give the hobby a try. 🙃

        1. Hi Dari – thanks for joining in the conversation! You’re right it’s absolutely possible to build one without. One of our longest lasting terrariums didn’t have any charcoal in 🙂

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