The subtle art of terrarium care can take a while to master.
I mean sure, when perfectly balanced, terrariums can pretty much look after themselves. Being notoriously low maintenance is the main appeal right?
Unfortunately, lots of people tend to trip up in the early days of finding that balance.
I’ve built a wide variety of terrariums over the years (with plenty of experimental failures) and in the process identified all the main points where they go wrong.
In this guide, we’re going to cover each of the main terrarium care mistakes, and I’ll teach you how to avoid them.
Lets get into it!
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- Key Closed Terrarium Care Tips
- 1. Check for Humidity – Are You Underwatering?
- 2. Watch Your Watering – Are You Overwatering?
- 3. Is Your Terrarium Getting Too Little (or Too Much) Light?
- 4. Watch Out for Mold
- 5. Catch it Early – Remove Dead Leaves or Rotting Plants
- 6. Overgrown Plants? Trim Them Back
- 7. Is the Terrarium Glass Dirty? Give it a Clean
- Terrarium Care FAQ
- Over to You
Key Closed Terrarium Care Tips
1. Check for Humidity – Are You Underwatering?
Being a closed system, terrariums mostly water themselves if the conditions are right.
Of course, that’s provided you have enough water in the system.
The best way to identify this? Check the humidity. The amount of condensation on the terrarium glass is representative of how much moisture is in the air.
If your terrarium is approaching 80% or higher (as tropical plants really love) then you’ll find that the glass will be fogged up somewhat through the hottest parts of the day.
That means that if you’re not seeing any condensation, it probably needs a top-up. You can also check for wilting, dry soil, dried-out leaves, and a bunch of other indicating factors.
On the flip side, if there are consistent heavy droplets present – you’ve gone too far. Which leads me to the next issue.
2. Watch Your Watering – Are You Overwatering?
Over-watering is a much greater risk than under-watering.
It’s very easy to do in a closed terrarium, and unfortunately very difficult to fix – so it’s best to add just a little at a time. Use a mister or spray bottle to water as evenly as possible, and just a few sprays at a time.
Heavy condensation is one indicator of overwatering, but it’s not the only one.
Remember, you never want to have a saturated substrate. A very light moisture is all you need. If the soil looks dark and wet, you’d be best off opening up your terrarium and letting it dry out a little.
Though the individual care of your terrarium plants will depend on the species, most need consistent light moisture.
If you’re using a drainage layer, you can also check how full it is. Ideally, you’ll have none or very minimal excess water pooling there.
👉 See my full guide on How to Water a Terrarium.
3. Is Your Terrarium Getting Too Little (or Too Much) Light?
Sunlight is essential to plants in a terrarium (they’re still plants after all), but let’s not forget that the glass container is essentially a greenhouse.
It’s all too easy to scorch your plants in direct sunlight…
Just be mindful of where you’re putting your terrariums and what kind of light your plants need.
The gold standard for most tropical plants is considered to be bright indirect light. Something you could comfortably ready a book in, but wouldn’t feel the warmth on your skin.
On the flip side, though many terrarium plants tend to be considered “low light,” that absolutely does not mean no light. You need to be giving them something to work with.
A North-facing window is a good bet for consistent indirect light, or pop your terrarium a few feet away from a stronger light source. Alternatively, artificial lighting makes this all so much easier.
👉 See my Guide to Terrarium Lighting for more help.
4. Watch Out for Mold
Mold is the silent enemy waiting in the shadows of all terrariums.
I can relate to mold, as I thrive in hot and humid environments too. Just like a wave of British tourists flocking to Spain in the summer, mold can quickly take over and ruin a beautiful environment.
That being said, a spot of mold doesn’t immediately spell disaster. After all, it’s part of a natural decomposition cycle – it shouldn’t affect healthy plants.
It’ll often go away on its own after a few weeks, and getting some more airflow in always helps.
Some people like to deal with small patches using a Q-tip and some hydrogen peroxide. Just a quick wipe should do the trick.
Whereas I prefer to tackle the problem at its source, with the help of a bioactive cleanup crew. Grab yourself some springtails on Etsy and let the mold-munching machines take care of the job for you!
(I also like to spray my terrariums occasionally with chamomile tea, as it contains sulphur compounds that can help keep mold at bay).
I’ve had some driftwood branches get covered in thick mold, and despite a few interventions of boiling and scrubbing, it came back again and again. In the end, I let it go its course and it simply went away after a couple of weeks.
👉 See my full guide to tackling terrarium mold if it’s a persistent issue you’re dealing with.
5. Catch it Early – Remove Dead Leaves or Rotting Plants
Plants die, it’s natural.
Don’t take it personally, but please do act on it.
Terrariums generally don’t have the capacity to deal with it in the same way as a natural environment would. They lack the biodiversity of organisms needed to effectively break down organic material.
If left unchecked, any dead plant matter will simply rot. Leaving your terrarium a smelly and unhealthy mess.
That’s why I always recommend removing plants at the first sign of rot… or death. It’ll help to maintain the balance and reduce the chances of a disastrous rot spreading through your plants.
Having a bioactive cleanup crew can help here too!
6. Overgrown Plants? Trim Them Back
Sure, we all want healthy, happy plants in our terrarium. We should try to create the best conditions possible for them to grow, but terrariums are peculiar things in that we generally don’t want our plants to grow too well.
Over the course of years, almost all terrariums will need some plant intervention (except for maybe moss terrariums).
Maintaining the balance is important.
Though you want some room for plants to grow in and settle in the environment, you still want to preserve the sense of space and scale you created in the beginning.
After all, plants need space to thrive, and we’re mostly restricting them in that sense. They also need light and water, both of which can be altered through excessive plant growth.
Here’s what to look for:
- Plants growing against the side of the container.
- Plants becoming so thick and bushy that they begin to block light from reaching others.
- Plants growing so tall they reach the top of the container.
- Fast-growing plants that are beginning to take over.
You can even prune a plant’s roots to slow its growth.
7. Is the Terrarium Glass Dirty? Give it a Clean
Nobody likes dirty glass, and neither do your plants.
Not only does it look awful (and half the fun of terrariums is being able to see them) but it can also restrict the light that the plants receive.
Give the inside of the glass a clean with a lint-free cloth and some warm purified water to remove any fibres.
Watering your plants with hard tap water (high mineral content) is generally fine for your plants, but it can leave a white calcium residue on the glass. Which is why I recommend watering your plants with purified water; deionised, distilled, carbon filtered – they’ll all do the trick.
Deinoised water is probably the cheapest and most freely available (here’s a bottle on Amazon).
Terrarium Care FAQ
Terrariums die for all kinds of reasons, but you’re best off starting with the most common problems and working your way backwards to identify the culprit. Making sure your plants have the right amounts of water and light are a good place to start.
Learning the basics of terrarium care will go a long way, but applying them to every terrarium will be different. Over time, you’ll come to understand the nuances of each terrarium, and you’ll be able to better identify when things are going wrong.
Terrariums do have an earthy smell (after all, they are earth) but any hint of an unpleasant odour is an indicator that something nasty is brewing.
Over to You
Getting your terrarium perfectly balanced isn’t always as easy as it seems. In our Essential Guide to Tropical Terrariums we’ll help you get it right from the start to finish and beyond.
If you’ve already run into problems, why not check out our Terrarium FAQ’s page?
Or, do you have any routines or care practices to help us keep our terrariums looking and feeling their best?
Let us know in the comments.