The single most common way to kill a terrarium is overwatering — so if you take one thing from this guide, let it be this: when in doubt, wait. Unlike a potted plant, a terrarium (especially a closed one) holds onto moisture, and there's no drainage hole for excess water to escape. The right amount is almost always less than your instincts say.
Closed terrariums: rarely, if ever
A closed terrarium recycles its own water in a sealed loop of evaporation and condensation. Once it's balanced, it can go weeks or even months without watering — some thrive for a year or more untouched. You don't water on a schedule; you water only when the terrarium tells you it's thirsty.
How to read the glass
- Light condensation that clears during the day → perfect balance. Do nothing.
- No condensation at all for several days → too dry. Add a light mist.
- Heavy, permanent fog you can't see through → too wet. Take the lid off for a few hours to vent, then reseal.
When you do water a closed terrarium, use a fine mist, not a pour — just enough to lightly dampen the moss and substrate. Our guide to terrarium humidity control goes deeper on getting this balance right.
Open terrariums: like a houseplant
An open terrarium has no lid, so moisture escapes and you water it more like a normal pot — roughly every one to two weeks, adjusted to the plants:
- Succulents & cacti: sparingly — every 2–3 weeks, and let the substrate dry fully between.
- Tropical open terrariums: more often — when the top of the substrate feels dry.
- Air plants: a soak or mist a couple of times a week, as they take water through their leaves.
Not sure which type you have? Compare the two in our guide to open vs closed terrariums.
What kind of water should you use?
Filtered, distilled or rainwater is ideal, especially for moss, which can be sensitive to the minerals and chlorine in tap water. If you only have tap water, letting it sit out overnight helps some of the chlorine dissipate.
Signs you're overwatering
Watch for permanent fog, mould, mushy stems or a swampy smell — all signs of too much water. If you spot them, vent the terrarium to dry it out and hold off watering. Our troubleshooting guide covers the fix for each.
New to terrariums?
Start with our complete step-by-step build guide and get the foundations right.
How to Make a Closed Terrarium
Frequently asked questions
How often should you water a closed terrarium?
Rarely — often just once every few months, if at all. It recycles its own moisture, so only mist lightly if the glass stays completely clear with no condensation for several days.
How often should you water an open terrarium?
Roughly every one to two weeks. Succulent terrariums need less; tropical ones need more. Let the top of the substrate dry between waterings.
How do I know if my terrarium needs water?
Read the glass. Light condensation that clears each day is ideal; no condensation means too dry. In an open terrarium, check whether the substrate surface has dried out.
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