How to Use Activated Charcoal For Houseplants

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Charcoal is one of those things that’s kinda important, but also, it’s the first thing to go when I’m making potting mix but don’t want to spend too much money.

It’s like the HR department of the soil world – you know, deep in your heart, that it’s important, but only if a problem arises. So I tell myself a problem will never arise. And if a problem does arise, I pretend that charcoal wouldn’t have helped anyway.

I am a terrible plant person.

Should I use activated charcoal or horticultural charcoal for house plants?

Ok, let me be honest here – I actually thought they were the same thing.

The reason I never bothered to check until now was that I was always recommended activated charcoal, so I assumed activated and horticultural were synonyms.

The difference between the two is the way they’re treated – activated charcoal is heated to higher temperatures, so it expands and contains lots of air pockets.

I assume similar to the way they pop pyrite like popcorn/rice krispies to make it into perlite.

Both activated and horticultural charcoal are great, lightweight soil additives that aid drainage and help to balance the pH of your soil. It’s these properties that make them useful to add to terrariums and closed systems, which don’t get flushed through like plants in pots.

Activated charcoal has the added benefit that it’s very porous, so it can trap toxins and odours (they use it to treat poison victims).

I’ve looked at Amazon and the prices are similar BUT when you think about it…when you’re buying activated charcoal, which is v porous, you’re buying a lot more air.

Which I’ve already explained is beneficial to your plants but also feels like a bit of a scam. Because you’re paying for holes.

Never mind.

What is activated charcoal?

Activated charcoal is the same as regular charcoal (which is stuff that’s been burned) but it’s been superheated.

As to what ‘stuff’ they burned to make the charcoal…I don’t know. They won’t tell you. Let’s hope it’s wood, and not, like bone char.

It looks like little black granules, and the heating process has made it nice and shiny, AND less prone to leave black marks everywhere than regular charcoal.

Why is activated charcoal good for house plants?

Activated charcoal improves drainage

It’s another gritty, air pocket-creating drainage aid that stops too much moisture being trapped in the soil.

Whilst it’s definitely an advantage, if you’re only after good drainage, there are cheaper things to add than charcoal (such asperlite).

Activated charcoal balances the pH of the soil

So I tried to research how activated charcoal balances soil, and it doesn’t magically balance it, it just lowers it – I’m assuming most soils err on the alkaline side, but I’m not a soil expert, I’m afraid.

If you’re interested in a bit more detail, here’s a nice article that’s more in-depth than this, but not quite at research-paper depths.

Activated charcoal neutralises smells and bacteria

Some of the time I steal the activated charcoal my boyfriend gets for his aquarium (he steals my leca, and we both pretend we don’t mind).

Activated charcoal is used in aquaria to absorb all the nasty bacteria that rocks up occasionally. It acts like a sponge for stuff you don’t want – hence why it’s given to people that have taken overdoses – and, I believe, neutralises it (to a certain extent).

It does the same thing to plants, but whilst it’s a pretty necessary part of a lot of aquarium filters, it’s not AS necessary in plant soil. Simply because we don’t have fish pooping in our plants all day long.

It’s a soil AMENDMENT rather than an actual necessity, but I like to use it when I can because it makes me feel professional.

How to use activated charcoal

Just mix it in with your soil.

I only use a small amount purely because it’s expensive* so I never buy as much as I need.

Ideally, you’d use one part charcoal to 5 parts coir (there’s a recipe in this post), but I usually just add a handful (or whatever paltry amount I have left in the bag.

*It isn’t expensive, per see. Its just more expensive than the other ingredients for a smaller amount plus it’s *kinda* optional.

Can you use grill charcoal for plants?


For a start, it could have been treated with unknown chemicals.

Also, it’s so so messy. Black marks EVERYWHERE.

But the main reason is that it will do the opposite of what we want the charcoal to do, which is raise the pH of the soil.

No charcoal at all is preferable to using grill charcoal on plants.

Is it necessary to use activated charcoal for plants and terrariums?

Plants, no.

I would recommend using it, but it isn’t 100% necessary.

It also isn’t *necessary* for terrariums, but it’s much, much harder to sort out pHs and bacteria etc when you’re dealing with a terrarium over a plant pot.

We have animals (a millipede, a frog, and a million-ish assorted isopods, springtails, and assorted bugs) in our terrarium so we need to make sure the environment is pretty much perfect for them, so an activated carbon layer was a no-brainer.

If you’re going to the trouble of setting up a terrarium, even if it just has plants, you may as well add the carbon, because it’ll be a pain if you decide to add one later down the road.

When we set up the terrrium we did a lot of reading on how effective charcoal actually is, and…everyone has a different opinion. The common consensus is that is does work in terms of reducing bacteria and mould BUT it ‘fills up’ as it were, pretty quickly, and becomes ineffective pretty quickly.

Where to buy activated charcoal

Amazon does it pretty cheap, but it’s always worth checking out your local garden centre, since they often have things for waaaaay cheaper than anywhere else.

One thing I noticed when adding the Amazon link is that in US there is a LOT of horticultural charcoal for sale, and not so much activated. Or, the activated charcoal comes in the form of capsules or odour reducing bags. Interesting.

Will activated charcoal stop root rot?

Er, no, not by itself.

It may help to kill off the bacteria that cause root rot, but if you continue to do whatever it was you were doing that cause the root rot in the first place, you’re just going to go round in circles.

Adding activated charcoal to plant with root rot can definitely help it, so it can be a good way to salvage plants in the reduced section that you suspect of having root rot, but it’s not an ‘easy’ way to fix it.

Activated charcoal is a great soil amendment, especially for terrariums, and it can help regular potted plants by improving their drainage and lowering the pH of the soil.

It’s only an amendment though, and you won’t notice a vast overnight improvement if you add it to your soil.

Hence my sporadic if-funds-allow approach to its usage!

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

3 thoughts on “How to Use Activated Charcoal For Houseplants”

  1. It needn’t be an extra expense if you already use things like Brita filters in your own water. Once they have outlived their usefulness in the pitcher, I take the time to deconstruct the filter and dump the material inside in my garden pots. If you are just going to throw them out anyway, why not take advantage of the value as an amendment, even if the activated charcoal isn’t as “active” as it once was when new?

    It also was a surprise to discover that my cut flowers got a great benefit from the vase having some of the stuff at the bottom. Not only did it allow for less sliding around in the arrangement stage, which was my primary reason for adding it in the first place, it had a surprising effect of keeping the water crystal clear and the flower fresh a great deal longer than they otherwise would last. I will try it again to see if I can repeat that result, and if so, it will become a default add to my vases of tulips every spring…

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