Closed terrariums are meant to be the ultimate low-maintenance bit of greenery — seal them up and let the little ecosystem look after itself. But after a year or two, even the best-behaved terrarium can start to look sorry for itself.
Maybe the plants have shot up and are squashed against the glass. Maybe the moss has turned from lush green to a sad, yellowing mat. Or maybe you've spotted the thing every terrarium owner dreads: fuzzy white mould creeping across the soil.
The good news? A tired terrarium isn't a dead terrarium. In most cases, a proper refresh will bring it straight back to life — and it's a far more satisfying afternoon than you'd think.
Here's how to do it.
How do you know when a terrarium needs refreshing?
Terrariums rarely fail overnight. They drift. Here are the signs it's time to step in:
- The plants have overgrown the glass. Foliage pressing against the sides traps moisture and leads to rot.
- The moss has yellowed or died back. Once cushion moss browns off, it rarely recovers on its own.
- Mould or white fuzz has appeared. A little is normal early on, but spreading mould means the balance is off.
- The soil smells, or water no longer drains. Compacted, sour soil starves the roots.
- It just looks tired. Sometimes nothing's "wrong" — it's simply lost its spark.
If you're nodding at two or more of these, a refresh is the answer.
Should you patch it up or do a full refresh?
This is the question we get asked most — and the honest answer is: a full refresh almost always wins.
It's tempting to snip a few leaves, scrape off the mould and hope for the best. But terrarium problems are usually symptoms of the same root cause: an environment that's fallen out of balance. Spot-treating the moss while leaving tired soil and crowded roots in place tends to mean the same problems are back within weeks.
Stripping it back to fresh foundations — new soil, new charcoal, healthy plants — resets the whole system. It takes a little more effort up front, but it's the difference between a terrarium that limps along and one that thrives for another two or three years.
What you'll need to refresh a terrarium
To do the job properly, you'll need:
- Fresh terrarium soil (formulated for humidity-loving forest plants, not standard potting compost)
- Activated charcoal to keep the new ecosystem clean and odour-free
- Drainage gravel for the base layer
- New plants and living cushion moss to replace anything past saving
- A little patience and a steady hand
You can source all of these separately — or save yourself the hunt and use a kit that's measured out for exactly this job. (More on that below.)
How to refresh a closed terrarium, step by step
1. Empty it out
Remove the plants, moss and decorative bits. Set aside anything still healthy — you may be able to replant it. Bin anything mouldy, mushy or yellowed.
2. Clean the glass
Wash the container in warm soapy water, rinse thoroughly and dry. This clears out lingering mould spores that would otherwise start the problem all over again. For stubborn water marks or limescale, a little diluted white vinegar works well — just be sure to rinse it off completely and dry the glass before you replant, as any residue left behind can harm your new plants once the terrarium is sealed.
3. Rebuild your layers
Start with a drainage layer of gravel, add a scatter of activated charcoal, then a generous layer of fresh terrarium soil. These three layers are the foundation of a healthy closed terrarium — get them right and the rest follows.
4. Replant
Position your new plants, firming them gently into the soil. Add cushion moss around the base for that lush forest-floor finish. Tweezers or a long tool help if your container has a narrow neck.
5. Water lightly and seal
A light mist is all it needs — closed terrariums recycle their own moisture. Pop the lid on, set it somewhere bright but out of direct sun, and watch it settle in.
How do you stop mould coming back?
Mould thrives on stagnant, overly wet conditions and decaying matter — so prevention comes down to balance:
- Use activated charcoal. It's your first line of defence against mould and odours.
- Don't overwater. Condensation on the glass means there's plenty of moisture already.
- Give it light. Bright, indirect light keeps plants healthy and discourages fungus.
- Remove dead leaves promptly. Decaying matter is what mould feeds on.
Get these right and your freshly refreshed terrarium should stay looking good for years.
The easy way to refresh your terrarium
If you'd rather skip the guesswork of sourcing soil, charcoal, gravel and plants separately, we've put together everything you need in one box.
The Terrarium Refresh Kit contains fresh terrarium soil, drainage gravel, activated charcoal, decorative pebbles, living cushion moss and four hand-picked terrarium plants — measured out for closed containers from 10L–20L. Everything arrives ready to strip back, replant and bring your terrarium back to life, with simple step-by-step instructions included.
It's the same trusted contents as our best-selling starter kit, put together specifically for breathing new life into a terrarium you already own.
