Best plants for terrariums: humidity lovers for closed jars, succulents for open bowls

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The most common reason a terrarium fails is not care but casting: plants were chosen for how they looked in the shop, not for the conditions inside the glass. A closed jar is a small, humid, fairly still world with moderate light; an open bowl is dry and airy. Pick plants that want what the container gives them, and most of the work is done.

What makes a good closed-terrarium plant

Likes high humidity and evenly moist soil.
Stays small or grows slowly, so it does not hit the lid in a month.
Copes with bright, indirect light rather than needing direct sun.
Tolerates being trimmed, because sooner or later everything needs cutting back.

Plants that usually do well in closed jars

Fittonia (nerve plant): veined leaves in pink, red or white. It wilts dramatically when dry and revives quickly, which makes it a useful gauge. Look for the dwarf types.
Small ferns: button fern, small maidenhair types and dwarf forms of other ferns enjoy the humidity. Some grow larger than the label suggests, so check the mature size.
Peperomia: the small-leaved trailing and compact kinds are slow and tidy.
Pilea: small-leaved species such as baby's tears and aluminium plant spread gently and can be trimmed.
Selaginella (spikemoss): feathery, moss-like and fond of humidity.
Ficus pumila (creeping fig): a small-leaved climber that will cover a back wall of soil or wood, but needs regular cutting back.
Small orchids and miniature begonias: rewarding in larger closed cases once you have some experience.
Mosses: cushion, sheet and other mosses carpet the floor and keep it evenly damp.

Plants sold as "mini" or "terrarium" plants in garden centres are often just young plants of larger species. Read the label for the mature size or look the species up before planting.

What makes a good open-terrarium plant

Wants the soil to dry out between waterings.
Prefers good airflow and lower humidity.
Needs plenty of light, often more than a room away from the window can give.

Plants for open bowls

Succulents: echeveria, haworthia, gasteria, small aloes, sedum and crassula. Haworthia and gasteria cope with less light than most and suit a bright windowsill that misses some sun.
Cacti: small, slow species, planted with gloves or tongs.
Air plants (Tillandsia): they need no soil at all and can sit on top of gravel or wood. They still need watering, usually by soaking or misting, then drying off quickly.

Succulents belong in open containers only. Sealed in a humid jar, they tend to stretch, go soft and rot from the base.

Plants to avoid

Anything fast and large, such as many common vining houseplants, unless you are happy pruning every week.
Flowering plants that drop petals, which rot on wet soil.
Mixing desert and tropical plants in one container. One group will always be unhappy.

Arranging for scale

Use one taller plant as a focal point, one or two medium plants, and something low or creeping to fill gaps. Odd numbers usually look more natural than pairs. Leave bare space for moss, stones or a piece of wood; a crowded jar becomes a tangle within a season and has poor airflow, which invites mould.

Buying healthy plants

Check the leaves and the underside for pests, and the soil surface for mould or tiny flies before you buy. It is worth keeping new plants in a pot on their own for a week or two before they go into a sealed jar, where any problem spreads fast. Tell us which plants have thrived or sulked in your jars, or ask what would suit a container you have, in the comments.