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Closed or open terrarium: match the plant to the lid

Updated: 21 October 2026

You are holding a cork, a hinged flap, or a plastic bowl, and the shop title has listed succulents and ferns in the same breath. Closed or open terrarium is that choice: humid foliage under a lid that holds moisture, and succulents or cacti in a case that can dry. The shape of the glass does not decide it. The [terrarium comparison](/hub/houseplants/terrarium) shows what each listing includes. Layer depths stay on [how to plant a terrarium](/hub/houseplants/terrarium/sub/terrarium-how-to-plant). Peter F. matched the plants on 21 October 2026. This is not a lab test. A qualifying purchase can earn a commission at no extra cost to you.

You are holding a cork, a hinged flap, or a plastic bowl, and the shop title has listed succulents and ferns in the same breath.

Our top picks

Clementoni Clementoni Harry Potter kit, 7+

Best overall

Clementoni Clementoni Harry Potter kit, 7+
5.5/10about £12.90
View offer
PYEF CRAFTS PYEF CRAFTS 1 litre jar kit

Rank 2

PYEF CRAFTS PYEF CRAFTS 1 litre jar kit
7.4/10about £24.99
View offer
Homtone Homtone golden birdcage, 18 cm

Alternative

Homtone Homtone golden birdcage, 18 cm
6.1/10about £32.95
View offer
On this page
  1. 1.What closed means
  2. 2.What a door actually does
  3. 3.Condensation is not mould
  4. 4.The plastic kit is neither

What closed means

A closed terrarium, as Kew and the Royal Horticultural Society use the word, is a lid that keeps humidity around small tropical foliage, ferns and moss. Kew puts cacti and succulents on the open side. The RHS wants bright indirect light, not direct summer sun, and water only a few times a year on a sealed jar. BBC Gardeners' World’s closed examples include Fittonia, ferns, Calathea, a miniature orchid and African violet. Cacti, echeveria, aloe and haworthia sit on the open list. The PYEF jar is the closed object here: 1 litre, about £24.99, with a cork reviews say fits. The title’s succulent words do not make that cork safe for a cactus.

What a door actually does

A hinged door lets your hand in. It does not make a bottle garden. The Homtone birdcage is about £32.95, brass and glass, 18 × 18 × 23 cm, sold empty. UK reviews say the opening is too small for a nursery pot, and that water leaks if you water freely. One buyer added a tray. A separate listing prints not watertight. That sentence is not on the Homtone spec table. Leave the flap able to vent for cacti or echeveria. Ferns and moss want a different seal. The lead-free solder line is the maker’s wording, not a British Standard.
Clementoni Clementoni Harry Potter kit, 7+

Testsieger

Clementoni Clementoni Harry Potter kit, 7+
5.5/10about £12.90
View offer

Condensation is not mould

A light fog is water, not growth. BBC Gardeners' World leaves a closed jar alone when condensation covers up to one third of the glass, and says wipe above that. Almost none, they say about a tablespoon. The Royal Horticultural Society reads no condensation as a possible need for water. Kew reads a fogged pane as too much water. Use those as separate rules of thumb. One PYEF review found the lid misting after the instructions. If the white on the soil is fuzzy, use terrarium mould.

The plastic kit is neither

The Clementoni set is neither a closed ecosystem nor an open succulent case. It is about £12.90, for ages 7–16, a plastic bowl with seeds, plaster and paints. UK reviews describe clover or cress, mould, and a hut that soaks up water. Buy it for a supervised seed build. Check plants, litres, the door and the glass before you pay for the photograph.

Common questions

Can succulents live in the PYEF jar with the cork on?
No. That jar is a closed 1 litre cylinder, and Kew and the Royal Horticultural Society keep succulents and cacti out of a tight lid. The title’s succulent wording does not change the cork. Use one small humid plant, such as a Fittonia or a fern, or leave the cork off and accept that you no longer have a closed terrarium. A 1 litre jar is still tight for a large succulent even when it is open.
Is a hinged birdcage a closed terrarium?
Not in this set. The Homtone case has one door that UK reviews call too small for pots, and other UK reviews report leaks when you water freely. A flap that can stay open is closer to an open container. Use it for small succulents you already own, with spare water, or skip it if you needed a corked humidity for moss and ferns.
Which plants suit a lid?
Small, slow, humid plants. Kew names tropical foliage and mosses under a tight lid. BBC Gardeners' World’s closed examples include Fittonia, ferns, Calathea, a miniature orchid and African violet. Cacti, echeveria, aloe and haworthia sit on BBC’s open list. Do not put one from each list into the same sealed litre.
How much condensation is enough?
Publishers do not agree. BBC Gardeners' World leaves a closed jar alone when fog covers up to about a third of the glass. The Royal Horticultural Society treats no condensation as a possible need for water, and heavy condensation as a reason to vent. Kew treats fog as too much water. Watch the pane for a couple of days after a mist, and do not invent a single percentage that all three share.
Why did the closed lid mist up straight away?
The compost or the plant was wetter than the jar could hold. One PYEF review reported misting even after the instructions. Wipe the excess and vent until the glass is only lightly fogged, using the BBC and RHS pictures as separate guides. Direct sun on the glass makes this worse. A soaked jar in the first afternoon is a watering problem, not proof that the cork has failed.
Can a child kit be a closed ecosystem?
No. The Clementoni bowl is plastic, vented in the way a two-part toy is vented, and planted with seeds that UK reviews call clover, cress or grass. It is a short project for ages 7–16. Mould in that bowl is a seed-kit complaint, not the condensation cycle of a corked glass jar. Do not seal it and expect a houseplant.
Where should a sealed jar sit, and where should succulents sit?
Both want bright indirect light. The Royal Horticultural Society names that, and says not direct summer sun. A north- or east-facing spot is their default for a bottle garden. Keep a closed jar off a hot windowsill where the glass heats. Succulents in the open birdcage can take a brighter sill than a corked fern, as long as you are not pouring water through a leaky base.

Related pages

Best terrarium

Terrarium

Terrarium buying guide: plants, litres, door, glass

How to plant a terrarium: layers, then a light mist

Terrarium mould: fog, white fuzz, and when to empty

Sources

Public UK sources named below. amazon.co.uk prices, stars and review counts on these three listings were read for this comparison. Page updated 21 October 2026. Other price bands are a 20 October 2026 snapshot, not a market average.

  1. RHS, Terrariums and bottle gardens (retrieved 21.10.2026)
  2. Kew, Make your own terrarium (retrieved 21.10.2026)
  3. BBC Gardeners' World, How to make a terrarium (retrieved 21.10.2026)
  4. BBC Gardeners' World, Terrarium care (retrieved 21.10.2026)
  5. Consumer Rights Act 2015, goods rights (retrieved 21.10.2026)
  6. Which?, damaged goods in the post (retrieved 21.10.2026)
  7. GOV.UK, General Product Safety Regulations 2005 (retrieved 21.10.2026)
  8. GOV.UK, invasive non-native plants (retrieved 21.10.2026)
  9. terrarium.co.uk, why a terrarium goes mouldy (retrieved 21.10.2026)
  10. Small & Green, terrarium care (retrieved 21.10.2026)