Guide
Closed vs open terrarium
A closed terrarium keeps its own water: plants breathe it out, it beads on the glass and runs back to the soil. An open one loses water to the room and needs watering, but suits plants that rot in still, wet air.
| Closed (sealed) | Open | |
|---|---|---|
| Air inside | Near 95 to 100% humidity | Close to the room |
| Watering | Rarely: the water goes round | Regularly: about 0.1 cm a day of wet surface at 20 °C, more when warm |
| Suits | Ferns, moss, tropical plants | Succulents, air plants, anything that rots in damp air |
| Watch for | Glass fogged all day: too wet, open it a while | Drying out between waterings |
| Plants that only suit it | 8 of 49 | 7 of 49 |
How the simulator treats the lid
- Sealed: water goes round, out of leaves, onto the glass, back to the soil.
- Sealed air sits near 95 to 100% humidity.
- Open: water evaporates, faster when warm, dry or wide-mouthed.
- Venting lets some humidity and water out of a sealed jar.
- Glass fogs on cool mornings; fogged all day means too wet.
- Open evaporation
- 0.1 cm a day of wet surface at 20 °C
- Per °C warmer
- 7% more
- Lid gasket leak
- 0.02 air changes an hour
Plants for a closed jar only
These need the steady humid air of a sealed jar and struggle open.
- Jewel orchid, easy
- Krauss's spikemoss, easy
- Peacock spikemoss, easy
- Flask-shaped pitcher plant, moderate
- Rex begonia (miniature cultivars), moderate
- Shingle plant, moderate
- Maidenhair fern, demanding
- Tailed orchid (miniature Masdevallia), demanding
Plants for an open jar only
These rot or sulk in a sealed jar's still, wet air.
- Haworthia, beginner
- Air plant, easy
- Burro's tail, easy
- Button fern, easy
- Echeveria, easy
- Jade plant, easy
- Venus flytrap, moderate
The rest, 34 plants, are fine either way. The best plants for a closed terrarium lists every one that lives sealed.
More terrarium guides
- Best plants for a closed terrariumPlants that live sealed, easiest first.
- Best moss for a terrariumMosses for closed and open jars, and what they grow on.
- Terrarium layers explainedDrainage, barrier, soil and top dressing, and what each does.
- Terrarium drainage: LECA vs gravel vs lava rockEvery drainage material side by side.
- Mould in a terrariumWhy new jars fuzz, which mould matters, and how to stop it.
- Springtails vs isopodsThe cleanup crew compared: what each eats and where it lives.