How to Fix Mould in Terrariums (7 Easy Tips & Tricks)

Terrarium mould, our fuzzy mortal enemy. 

It’s always lurking, ready to strike. But is it actually a worry or just a nuisance?

Personally, I’ve encountered mould in just about every terrarium i’ve made. There’s always a signature mould “bloom” as new terrariums settle in.

So, I’m either super unlucky, a terrible terrarium maker or just maybe – it’s a pretty normal process.

In this article we’re going to look at why mould is not something to panic about, and I’ll offer some techniques to address it should you need to.

Terrarium Mould

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Is Mould Harmful to Terrariums?

Generally speaking, mould doesn’t affect healthy plants

If it starts to take over the whole terrarium then it becomes more of a problem, but a little bit of fuzz is not a serious threat.

Mould is a type of fungus, and fungi are saprotrophic. Meaning they are involved in the processing of decayed (dead or waste) organic matter.

Terrarium mushrooms fall into this category too, they’d all generally be feeding on fallen leaves and dead plants in the wild. 

So, as long as your plants are healthy, mould shouldn’t pose much of a risk to them.

However, you can still get a mouldy terrarium with healthy plants. Moulds feed on sugars and other moist organic matter. They can even feed on surfaces like plastics if a biofilm (bacterial layer) is present.

In my terrariums I see mould most often on driftwood branches, and that’s totally normal.

Truth be told, it can get a little out of hand

Mould is a somewhat frequent reality in the terrarium hobby, but thankfully it’s more of a nuisance than a problem.

It’s like a bad neighbour. It shows up to annoy you every time you make something nice, but if you give it some air and ignore it long enough, it’ll often go away on its own eventually.

Where Does Terrarium Mould Come From?

Mould is a natural phenomenon, it’s everywhere.

All it needs to flourish is a warm, moist environment with plenty of organic matter to feed on. In other words… a terrarium.

Sadly, mould is one of those things that’s very hard to eliminate completely, because it reproduces via microscopic spores. These things can lay dormant for long periods of time, and spread through the air to form new colonies all over.

Spores can enter your terrarium via:

  • Soil – Probably your most likely culprit. Some soils come sterile packed so they’re sure to be clear, but random assortments of soil mixes – and most definitely native soil taken from the wild – are likely to contain spores.
  • Plants & mosses – Spores can hitch a ride on top of plants and amongst mosses. There are some interventions to deal with mould colonies on plants, but there’s not really an effective way to cleanse plants and mosses of mould spores.
  • Hardscape branches – There’s a lot of sugars to be found in living woods, even if they’ve been treated or bleached over the years.
  • The air – If you have mould in your home (or wherever you build your terrariums) there’s a chance that there are enough spores in the air to germinate.

Mould can grow very quickly. 

Often if I mist down my terrarium, the very next day I’ll see some mould colonies on driftwood. 

Most moulds need a water content of over 70% to start germinating. So generally, it’s the surfaces where water beads or gets absorbed that are most at risk.

Got a Mould Outbreak? Here Are Your Options

#1 Add some springtails – These beneficial terrarium insects love to eat mould (and not your plants) so introducing a colony will do wonders in keeping your terrarium healthy and happy.

Springtails Culture
My springtail culture ready to be added to a terrarium (some of it at least).

This really is the best option in the list, as it works as both a solution and a deterrent. You can grab springtails on Etsy, or isopods work too.

#2 Spray with chamomile tea – Chamomile tea is actually a mild organic fungicide thanks to its rich sulphur compounds. Personally, I didn’t find this was potent enough to halt the spread of mould on my driftwood branches, but I’m convinced it helps prevent outbreaks amongst the plants when regularly applied.

The chamomile tea handily matches the colour of my old mister.

#3 Air it out – Mould thrives on moisture, opening up a closed terrarium and incsreasing air flow will reduce both the humidity and the total level of water in the container.

#4 Remove and quarantine – If the mould outbreak is localised to certain plants or hardscape elements, you can remove the affected objects and quarantine them elsewhere.

#5 Dab with hydrogen peroxide – Thanks to its fizzing action, hydrogen peroxide is an effective way to kill mould on porous materials. The 3% solution is sold in supermarkets and recommended across the web.

Simply dip a Q-tip in the solution and go to work! That being said, I’ve tried wiping mould away with Q-tips before, and it’s a real pain… You’ll need a lot of Q-tips and even more patience to get through a big outbreak this way. 

#6 Swap out the substrate – If you think the substrate is likely to be the cause, re-potting the whole terrarium in a sterile medium can significantly reduce the levels of mould.

My Recommendations

Honestly, I always recommend you add a springtail culture to a terrarium. It’s a cheap and effective way to never have to deal with mould. It’s a no-brainer really.

In the project for my Essential Guide to Tropical Terrariums, I chose to use springtails (along with solid building and watering practices recommended in the guide) and it hasn’t shown a hint of mould.

However, if you’re already dealing with an outbreak, what you do is going to depend on it’s severity.

For most outbreaks, I’d recommend simply getting more airflow into your terrarium and letting it dry out a little. I find most new blooms run their course in a couple of weeks.

A regular spray with chamomile tea is always a good idea too in my opinion. It doesn’t harm the plants, smells wonderful, and has a protective effect. 

The “getting out of hand” kind of outbreaks that don’t respond the above measures, may need a more serious intervention from the list.

Side note: Some people will claim that activated carbon/charcoal will prevent mould outbreaks as it purifies the water, but I’m not so convinced. I’m sure it helps a little, but given how ubiquitous mould spores are, I doubt a layer of charcoal at the bottom is enough to cleanse the whole system.

Over to You

Do you have an effective means of stopping mould in terrariums? I’d love to hear it.

I’m also interested in hearing any stories where mould has completely ruined a terrarium (for science of course!).

Good luck and stay safe out there!

33 thoughts on “How to Fix Mould in Terrariums (7 Easy Tips & Tricks)”

  1. I made my first paludarium which has flowing running water streams and one big pond at the bottom. It’s been a nightmare with white mold causing me health problems like heart palpitations and insomnia. Just going to get rid of it despite it’s beauty, 5 year old bonsai, and spending 300$ to make it.

    1. I’m so sorry to hear that Kyle! Your paludarium sounds stunning. I imagine trying to manage mould in a container with still water, running water and earth (at a variety of water saturations) must be a real challenge.

  2. Ive got a question if my driftwood got mold on it and i just removed it completely, removed my substrate and used paper towels for a little while, and disinfected my terrarium would that kill off the mold or keep the mold from developing? Is the driftwood the only problem? will it come back even if i put paper towel for little while and if i have no driftwood at all?

    1. Hi Issaq, to be honest I don’t think you can ever fully prevent mould from occurring in terrariums. The driftwood isn’t so much the cause, but more so the catalyst. Mould is much more likely to bloom on driftwood because the surface is full of exposed sugars and it tends to absorb a lot of moisture.

      So, to answer your questions;
      1. Removing and drying everything would probably kill off the initial mould bloom, but wouldn’t necessarily stop it coming back (it didn’t for me) as it’s near impossible to destroy all the spores.
      2. Driftwood is not the only source of the mould, but is likely to be a driving force behind it. Removing the driftwood altogether may help, but again, can’t guarantee it will stop it.

    1. That’s a good question! You could certainly argue that a layer like that would be separating the moisture in the soil from the air, so it might indeed reduce the ability for the mold to form. Worth a try 😊

  3. It looks like my succulents are not in any type of soil. It looks like black small stones. These stones are now turning green. I would assume this is a type of mold. Can you suggest how I would clean this up or have to change the medium.

    Thank you

    1. Hi Sandi, I don’t have much experience with succulents I’m afraid, but I know that mold can only thrive in damp environments. I’d imagine letting it dry out for a prolonged period (succulents should be able to handle this) would cause the mold to naturally die off.

    1. If it’s just a bit of white fuzz, usually just a couple of weeks. If it’s something much thicker and darker, you may need to take a direct approach, e.g. airing out the terrarium.

  4. I found some woody vines I want to use in my tree from terrarium and I was honestly thinking about putting a thin layer of silicone around them in case they mold out and don’t hold up to the moisture. Do you think that would prevent this from happening if I dry the vines out?

    1. Hey Joe, can’t say I’ve ever tried covering wood in a protective layer of silicone before! I’d imagine it would work to stop mould (as it would be sealed off from the air and moisture) but it sounds like a messy process!

  5. Hi Dan so I’ve just completed putting together my first terrarium for a crested gecko. I have springtails and Isopods in it already and am planning on getting the gecko soon but just found some pale green fuzz on the bottom of my cork bark backing and one branch of driftwood. It’s not bad and I’m hoping my bugs take care of it but what are some suggestions when adding in a reptile addition.

    1. I’m afraid I don’t have much experience with animals, just plants! I’d imagine the springtails and isopods will make short work of the mold, but I daren’t speculate on how it might affect a gecko.

  6. Yo, to all of you terrarium, vivarium, and palidariumists out there with mold taking your tanks over, ultraviolet and infrared light fixtures massively reduce and sporous fungi, whether pre or post germination. Technically speaking, these are usually marketed as aquatic algae combatants, but they don’t function exclusively as such. It’s the reason so many aquarium filters have UV/IR bulbs in them. This can apply, equally effectively in my experience, to terrariums, as light can travel through air as easily as water. Assuming the majority of you have planted tanks, you’d already have a light fixture, just look for a bulb at a PetSmart or whatever’s closest. I personally have multiple setups with humidity levels above 80%, some of them with a constant feed of fog/mist, and the four effective stops I use are isopods, charcoal in the misting systems, light fixtures, and most importantly, a well lit and ventilated tank. Hope this helps

  7. a seed on the rock bottom has germinated and is starting to grow upwards. i just wanted to ask if its roots will rot and be a problem for the terrarium.

    1. Good question! Depends on the plant I’d imagine, some plants will happily grow in water whereas others will quickly rot. If you can get it out easily, I probably would, but I don’t think it poses too much of a risk to the whole terrarium.

  8. Hi Dan, thank you for the information/advice. Six months into creating terrariums (open and closed), and mini-scapes, I have mainly been battling those pesky fungus gnats. Winning, I think!
    Recently acquired and used some beautiful driftwood pieces, and now noticing some mould forming in one closed terrarium, on the driftwood. I am prepared to see where it takes the terrarium and me though, before trying to treat.
    It’s all a learning curve and I am enjoying the adventure thus far. Cheers.

    1. Hi Robyn, you’re so very welcome! Sounds like you’re really taking to the art of terrariums 🙂 Driftwood can be a little finicky with mould at first. Even after boiling and scrubbing the wood it came back for me, but then after a few weeks in the terrarium it went away and stayed away (for over a year now).

  9. Hi Dan. I created my 1st terrarium with 4 plants (2 ferns, 1 polka dot plant & another plant (I can’t recall the name but it looks like lemon coral sedum & is supposed to spread like ground cover with a beautiful green chartreuse color. I used LECA instead of gravel at the bottom, then a mesh piece, then horticultural charcoal and then the potting soil. I wasn’t sure how much potting soil to use but wanted to be sure the root balls were properly covered. The container is 10 1/2″ in height with an opening at 8″. So, there is 4″ of soil in the terrarium now. Is that too much soil? Also, to top dress the soil, I used a preserved sheet moss I bought at Hobby Lobby. I’m guessing preserved sheet moss after staying wet will likely produce mold inside a closed terrarium. So, after reading your site & info this morning, I removed all the sheet moss and have the lid off with the soil exposed to “air out”. Can I buy living moss to top dress the soil from my local florist? Is there any moss at craft stores that won’t cause mold to top dress with since moss gives it such a finished landscaped look? Since this was the first time I created a terrarium, it’s been a learning curve for me and, of course, I would like to avoid mold issues if at all possible.

    Thanks for any advice. If having to re-do my terrarium means better success for terrarium & plants overall, then I will gladly re-do my terrarium to improve it if something needs to be corrected. Thanks again,.

    Thank you.

    1. Hey Nancy 🙂 To answer your questions; 4′ of soil sounds fine, yes you can often buy living terrarium moss from florists (I like bun moss best), not sure about getting moss from craft stores. In theory, all moss is at risk of developing mold but it’s not something to worry about up front. It sounds like you’re on the right track!

  10. Hi Dan,

    This past weekend I finally put together three terriaums and used activated charcoal, potting soil, sheet moss, drift wood and pebbles. I have a rabbit fern in one of them and for the other two I have some nerve plants. In about three days I noticed white fuzzy mold growing on the sheet moss and now on parts of my nerve plants (leaves) ….first reaction was, “Ahhhhhhhh nooooo.” After reading your advice I feel much better haha and will let it run its course. I look forward to one day not seeing the white fuzzy mold because at first glance it’s concerning. I will try airing out my terriaums as well.

    Thank you again for your advice!

    1. Hey Ash, it sounds like you’re on the right track! Adding some springtails can help a lot too, but I’m sure with some extra airflow it’ll work itself out eventually 🙂

  11. Hi Dan,

    I am new to the terrarium world, wanted to ask is there any pre-work need to be done before put all the plant, wood, stone and etc into a terrarium.

    Recently I complete my first terrarium which have the following:
    1. Volcanic stone False bottom
    2. succulent substrate
    3. Few driftwood
    4. 4 Succulent
    5. Moss

    However, it start growing mold on the driftwoord after a few day. Having a big headache now.

    1. Hi! Some people like to boil driftwood before adding it, but to be honest I’ve tried that and it didn’t stop the mold. Personally, I think all driftwood is prone to mold at first, but mine went away on its own after a while.

  12. Hi Dan,

    Thank you fro your post, it makes me feel so much better that mould is a common cause. I mean everything driftwood I use tends to bloom with mould.
    I read in the past that Cynamon is helpful it worked on driftwood, I sprinkled on top and let it dry for a day or two and then out back on my scape.
    But I didn’t know about camomile tea, and I might invest in some isópode too.
    Thank you so much for your post, vey insightful .
    Ana

  13. Hello, I’m new to the terrarium craft. I have a white mould on the bottom rock layers of my closed terrariums. Layers are big rocks, activated charcoal, pebbles, sheet moss, and soil. The one that has the biggest problem has an orchid and orchid bark, not soil. I have opened all the terrariums to air out. What should I do about the mould in the bottom layer?

    1. Sounds like a tricky place to target! I’d honestly try to let it dry out as much as possible and start adding chamomile tea to your water.

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