Closed terrarium: how to build one that lasts
A closed terrarium is a sealed or nearly sealed clear container with layered soil and small humidity-loving plants. Water evaporates, condenses on the glass and runs back into the soil, so a balanced jar needs watering only rarely — often every 3–6 months or longer. It wants bright, indirect light, no fertiliser and no succulents.
| Difficulty | Easy once the moisture is settled |
|---|---|
| Container | Any clear, lidded glass: jar, bottle or large case (not tinted or cloudy) |
| Light | Bright, indirect, at least 6 h a day; never direct sun |
| Watering | Only when condensation disappears — often every 3–6 months or longer |
| Typical plants | Cushion moss, Fittonia, Peperomia, Selaginella, Pilea, small ferns, jewel orchids |
| Cleanup crew | Springtails; isopods too in larger builds |
| Fertiliser | None |
What is a closed terrarium and how does it work?
A closed terrarium is a tiny water cycle in a glass box: light and warmth evaporate moisture from the soil and leaves, it condenses on the glass and trickles back down. Because little water escapes, the plants live on the same moisture for months.
The idea goes back to the London physician Nathaniel Bagshaw Ward, who saw a fern and a grass sprout inside a sealed jar he was using to watch a moth pupa. He had glazed cases built, sent British ferns and grasses to Sydney as a trial in 1833, and published his book on growing plants in closely glazed cases in 1842 — that is the publication year, not the discovery, which is why some sources date the terrarium to 1842. The 'Wardian case' became a Victorian parlour fashion and moved tea, cinchona and rubber plants around the world; Kew kept shipping living plants in them until 1962.
In MOKIZEN's analysis of 591 published layouts, 39 are terraria and 20 are moss-focused mossarium layouts.
Which plants work in a closed terrarium?
Pick small, slow-growing, small-leaved plants that love humid air, and never cacti or succulents — they rot in a sealed jar. For balance, combine something upright, something trailing or creeping and something in between, with moss as the groundcover.
- Sources disagree on philodendrons: Mississippi State lists them as suitable, Iowa State says common houseplants like them are not ideal. Choose the smallest, slowest plant you can find.
- Selaginella is among the most used plants in MOKIZEN's fairy and terrarium layouts.
| Role | Plants |
|---|---|
| Groundcover | Cushion moss and other land mosses, Selaginella |
| Low foliage | Fittonia, Peperomia, Pilea, polka-dot plant (Hypoestes), Saxifraga |
| Trailing | Creeping fig (Ficus pumila) — trim it often |
| Upright | Small-leaved ferns such as Asplenium, parlour palm (Chamaedorea elegans) |
| Accent | Jewel orchids (Ludisia and relatives), miniature African violets |
How do you build a closed terrarium layer by layer?
From the bottom up: a drainage layer, a thin layer of charcoal, a barrier, then soil and a living surface. Depths vary between sources — Mississippi State uses about 2.5 cm of gravel and 5 cm of mix, Iowa State 5 cm of gravel and 2.5–10 cm of soil, RHS a drainage layer plus about 5–7 cm of compost with grit. The practical envelope is below.
- Clean the container thoroughly.
- Add drainage, charcoal, the barrier and the soil.
- Plant from largest to smallest, making small wells for the roots and firming them in; keep leaves off the glass.
- Place stones and wood, then lay the moss surface.
- Water sparingly with a mister or small can: moist soil, never waterlogged.
- Settle the moisture before sealing (see below).
- Add springtails once there is a little organic matter for them to eat.
| Layer | What and how deep |
|---|---|
| Drainage | Gravel, pebbles, expanded clay or perlite, about 2–5 cm |
| Charcoal | Horticultural or activated charcoal, about 0.5 cm |
| Barrier | Mesh or a layer of moss so soil does not wash down |
| Soil | Light, free-draining mix, roughly 5–10 cm (sources range 2.5–10 cm); RHS adds about one part grit to four parts compost |
| Surface | Moss or bark, plus small stones, wood or cork |
Where should you put a closed terrarium?
Give it bright, indirect light for at least 6 hours a day — near an east- or north-facing window, or under a grow light — and keep it away from heaters. Direct sun on a closed glass box traps heat and cooks the plants.
How often do you water or open a closed terrarium?
Water only when the condensation disappears. Sources disagree on the interval — Iowa State says every 3–6 months, RHS a few times a year, Mississippi State that a balanced jar can go from weeks to years — but all agree on the signal: the glass has stayed completely clear and the soil feels dry. Then mist lightly.
Right after planting, do not seal it straight away. RHS leaves the lid off for the first week and half-closed for the second; Mississippi State alternates 24 hours lid on and 24 hours lid off until only light condensation forms. Either works — the goal is the same.
- Light misting on part of the glass: healthy.
- Heavy fog all day or water streaming down: too wet — open the lid for a few hours.
- No condensation at all: it needs a little water.
Why is there mould in my terrarium?
Mould usually means too much water, still air or something dead left inside. White fuzz on new wood in the first weeks is common and normally fades once the system settles and springtails arrive. For anything else, air the jar for a few hours when the glass stays fogged, wipe it, and pull out mouldy or dead material.
The cleanup crew is the long-term fix. Isopods such as dwarf white Trichorhina tomentosa or powder orange Porcellionides pruinosus shred leaf litter and dead plant matter; fungi colonise the fragments; springtails such as Folsomia candida graze the fungi and mould. One starter culture of springtails is usually enough, and the dwarf isopods suit small enclosures.
How do you look after a closed terrarium over time?
Once settled, a closed terrarium needs only a quick check each month. Do not fertilise: the whole aim is slow growth that stays in scale.
| When | Task |
|---|---|
| First 2–4 weeks | Watch for heavy condensation and mould; air it and remove dead material |
| Monthly | Check condensation, trim anything touching the glass or lid, remove dead leaves |
| Every few months | Mist lightly only if the glass has stayed clear and the soil is dry |
| Every 1–2 years | Replace or divide plants that have outgrown the jar |
What are common closed terrarium mistakes?
- Overwatering — rot, mould and yellow leaves. Water sparingly; if too wet, open the lid for hours or a day and wipe the glass.
- Direct sun — the glass traps heat. Use bright, indirect light only.
- Succulents or cacti — they rot in the humidity. Keep them for open containers.
- Large or fast plants — they press against the glass. Choose small, slow growers and trim.
- Leaving dead matter inside — it feeds spreading mould. Remove it and add springtails.
- Fertilising — it pushes growth the jar cannot hold.
Plants and animals in this guide
- Cushion Moss (Pillow Moss) (Leucobryum glaucum)
- Fittonia (Nerve Plant) (Fittonia albivenis)
- Peperomia (String of Turtles / Ripple Peperomia) (Peperomia prostrata / P. caperata)
- Peacock Spikemoss (Selaginella uncinata)
- Pilea 'Aquamarine' (Silver Sparkle Pilea) (Pilea 'Aquamarine' (sold as "Pilea glauca"))
- Creeping Fig (Ficus pumila)
- Jewel Orchid (Macodes petola / Ludisia discolor)
- Sphagnum Moss (Live) (Sphagnum spp.)
See it in 3D
Related guides
- Open terrarium: succulents and cacti in glass
- Paludarium: how to build a half-land, half-water tank
- Wabi-kusa: how to make and grow an emersed plant ball
Sources
- Wardian case — Wikipedia
- Terrarium — Wikipedia
- Terrariums and bottle gardens — Royal Horticultural Society
- How to design a closed-system terrarium — Mississippi State University Extension
- How to create and care for a terrarium — Iowa State University Extension (Yard and Garden)
- Bioactive terrarium — Wikipedia
- The clean-up crew — the bioactive terrarium — Exo Terra
- Springtails in terrariums — Terrarium Tribe
- How to fix mould in terrariums — Terrarium Tribe
- Aquascape insights (591 published layouts) — MOKIZEN
Written from these sources; last updated .
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