Build a closed terrarium for plants that love humidity, such as moss, fittonia, small ferns, and peperomia, and an open terrarium or bowl for plants that need dry air, such as succulents and cacti. Layer about an inch of drainage material, a thin barrier, an optional sprinkle of horticultural charcoal, and two to three inches of airy substrate, then plant, water lightly, and place it in bright, indirect light, never direct sun. A healthy closed terrarium shows light condensation for part of the day and needs water only every few weeks or months.
Closed or open?
| Closed terrarium | Open terrarium | |
|---|---|---|
| Humidity | High, recycles moisture | Room humidity |
| Best plants | Moss, fittonia, small ferns, peperomia, baby tears, miniature begonias | Succulents, cacti, haworthia |
| Watering | Every few weeks to months | Every 2 to 4 weeks, sparingly |
| Main risk | Mold and rot from too much water | Overwatering in a container with no drainage |
| Container | Jar or cloche with a lid or cork | Bowl, open globe, or wide vase |
Do not put succulents in a closed jar. They rot in the constant humidity.
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- Drainage layer, about 1 inch: clay pebbles (LECA), pea gravel, or lava rock. This gives extra water a place to sit away from roots.
- Barrier: a piece of fine mesh, landscape fabric, or a thin layer of sphagnum moss to keep soil from washing down.
- Charcoal (optional): a thin layer of horticultural charcoal. Many builders use it to absorb odors and buffer the drainage layer; it is not a cure for overwatering.
- Substrate, 2 to 3 inches: for closed builds, an airy mix with coco coir or peat, orchid bark, and some perlite. For open succulent builds, a gritty cactus mix.
- Plants and moss: use small plants that stay small. Tuck moss over bare soil.
- Cleanup crew (optional): springtails or isopods help break down dead leaves and mold in closed builds.
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Glass jars with lids for closed builds, horticultural charcoal for the base layers, and long-reach tweezers and tools for planting through narrow openings. We may earn a commission at no extra cost to you.
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Light
Bright, indirect light is ideal. Direct sun through glass heats a closed jar like a car and can cook the plants in an afternoon. A north or east window, or a small LED grow light on a timer for 10 to 12 hours, works well. Our guide to grow light basics covers placement.
Watering a closed terrarium
- Start light. After planting, water just enough to darken the soil. You can always add more.
- Watch the glass. Light fog in the morning that clears by afternoon is perfect.
- Heavy fog all day means too much water. Remove the lid for a few hours a day until it clears.
- No condensation at all and dry looking moss means add a few spoonfuls of water.
- Check the drainage layer. Standing water should never reach the substrate.
Open terrariums need a measured amount of water poured near the roots every few weeks, more often under grow lights and less in cool rooms.
Ongoing care
- Prune plants that touch the glass or crowd others, using long scissors.
- Remove dead leaves promptly so they do not mold.
- Wipe the inside of the glass with a paper towel on a stick.
- Do not fertilize closed terrariums except rarely, at very low strength. Fast growth just means more pruning.
Fixing mold and pests
A little white fuzz on new wood or dead leaves is common in the first weeks. Remove it, open the lid for a day, and cut back watering. Persistent mold on plants means the build is too wet. Fungus gnats can appear in moist builds; see fungus gnats on houseplants for control that suits small containers.
Safety notes
Use a sturdy container on a stable surface where pets cannot knock it over, since broken glass and wet soil are a hazard. Wear gloves when handling sharp lava rock and charcoal dust, and wash hands after handling potting mix. Some terrarium plants are toxic if chewed; place builds out of reach of curious pets and young children, and check the ASPCA plant list for the plants you choose.
Bottom line
Match the container to the plants: closed jars for moss and humidity lovers, open bowls for succulents. Layer drainage, a barrier, and airy soil, keep it out of direct sun, and water by watching the condensation. A good closed terrarium needs very little care once it settles.
Related reading
- Humidity trays and grouping winter houseplants
- Seed starting trays and humidity domes
- Air plant care and watering
- Spider mites on houseplants in dry heat
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