Closed terrarium plants

Humidity-loving tropicals: nerve plant (fittonia), moss, baby's tears, ferns like maidenhair and bird's nest, spikemoss, and colourful foliage such as rex begonia and polka dot plant. They all thrive in the warm, damp, still air a sealed jar creates. Avoid succulents and cacti — they need dry air and will rot.

No. Succulents and cacti store water and need dry air with good airflow; the trapped humidity of a closed terrarium rots them within weeks. Keep them for an open terrarium and fill a closed one with ferns, moss and fittonia instead.

Cushion moss for pillowy mounds and sheet moss for carpeting bare substrate are the two easiest. Both draw moisture from the humid air rather than roots, so they stay green with almost no effort in a sealed vessel — just use rain or distilled water to avoid mineral crusting.

Two or three in a small jar, a few more in a large one. Pick plants that share the same light and moisture needs, and leave room to grow — overplanting is the most common mistake and leads to crowding, poor airflow and mould.

Bright but indirect light is ideal — an east or north window, or a full-spectrum grow light in a dark room. Never direct sun: the glass magnifies it and cooks everything inside. Most closed-terrarium plants are shade-tolerant tropicals, so lower light suits them fine.

Nerve plant (fittonia) — it's cheap, compact and wilts dramatically when thirsty, then recovers within an hour of a mist, so it tells you exactly when something's wrong. Pothos and cushion moss are similarly forgiving first choices.