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.
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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 at its core, it’s 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 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. In fact, it’s every branch, every time…
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. Little bastards.
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
- 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.
- 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.
- 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.
- 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.
- Air it out – Mould thrives on moisture, opening up a closed terrarium and increasing air flow will reduce both the humidity and the total level of water in the container.
- Add some springtails or isopods – 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. You can grab isopods from Rubberduckyisopods.com and springtails from Etsy.
If possible, 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 not: Some people will claim that activated carbon 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.
Remember, it only takes one spore to fuck things up.
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! I’ve never encountered a case like this, but it’s always good to know a worst-case scenario if they exist.
Good luck and stay safe out there!