Terrarium mold, 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 mold in just about every terrarium I’ve made. There’s always a signature mold “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 mold is not something to panic about, and I’ll offer some techniques to address it should you need to.
This page may contain affiliate links that allow us to make a small commission (at no further cost to yourself). 💚 Thank you for helping to support the tribe!
Is Mold Harmful to Terrariums?
Generally speaking, mold 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.
Mold 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, mold shouldn’t pose much of a risk to them.
However, you can still get a moldy terrarium with healthy plants. Molds 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 mold most often on driftwood branches, and that’s totally normal.
Mold 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 neighbor. 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 Mold Come From?
Mold 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, mold 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 mold colonies on plants, but there’s not really an effective way to cleanse plants and mosses of mold spores.
- Hardscape branches – There are 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 mold in your home (or wherever you build your terrariums) there’s a chance that there are enough spores in the air to germinate.
Mold can grow very quickly.
Often if I mist down my terrarium, the very next day I’ll see some mold colonies on driftwood.
Most molds 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 Mold Outbreak? Here Are Your Options
#1 Add some springtails – These beneficial terrarium insects love to eat mold (and not your plants) so introducing a colony will do wonders in keeping your terrarium healthy and happy.
#2 Spray with chamomile tea – Chamomile tea is actually a mild organic fungicide thanks to its rich sulfur compounds. Personally, I didn’t find this was potent enough to halt the spread of mold on my driftwood branches, but I’m convinced it helps prevent outbreaks amongst the plants when regularly applied.
#4 Remove and quarantine – If the mold outbreak is localized 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 mold 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 mold 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 mold.
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 mold. 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 mold.
You could also start with a purpose-built container that comes with built-in fans and ventilation (like these from InSitu Ecosystems). They promote natural air circulation that replicates a jungle environment, making sure mold isn’t able to take hold.
However, if you’re already dealing with an outbreak, what you do is going to depend on its 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.
Finally, the “getting out of hand” kind of outbreaks that don’t respond to the above measures, may need a more serious intervention from the list.
Side note: Some people will claim that activated carbon/charcoal will prevent mold outbreaks as it purifies the water, but I’m not so convinced. I’m sure it helps a little, but given how ubiquitous mold 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 mold in terrariums? I’d love to hear it.
I’m also interested in hearing any stories where mold has completely ruined a terrarium (for science of course!).
Good luck and stay safe out there!