Hypoestes, the polka dot plant, is the simplest way to put colour into a terrarium: its green foliage is speckled with pink, white or red depending on the variety. It is easy and quick, with two quirks worth knowing — it loses its colours if it is short of light, and it wears itself out by flowering. Two habits are enough to keep it in hand.

At a glance

What it brings

Colour, in a world that has almost none. A tropical terrarium is a study in greens: moss, fern, fig. Hypoestes breaks that up with pink or white markings that catch the eye at once.

It plays the same part as fittonia, with a difference of pattern: fittonia is veined, hypoestes is speckled. Pairing them gives two registers of colour that do not repeat each other.

Light: what makes the colour

This is the point specific to this plant. The variegation is not fixed: it depends on the light received. Under insufficient lighting the markings fade and the foliage turns uniformly green again — the plant survives perfectly well, but the interest disappears.

So it needs bright, indirect light, stronger than a fern or a selaginella would ask for. An east-facing window suits it well, at about a metre away.

Never direct sun, which marks the leaves under glass — see Terrarium too warm.

Substrate and planting

An airy, slightly moisture-retentive terrarium substrate. Rinse the root ball in lukewarm water before planting, as with every terrarium plant.

Place it on the middle storey of the composition, visible from the main face: it is a point of colour, so it needs to be seen.

Pruning: two habits that change everything

Pinch out the tips. Hypoestes grows fast and runs upwards if you let it. Pinch the stems above a pair of leaves every six to eight weeks: the plant branches and forms a dense clump instead of a bare stem topped with a few leaves.

Cut off the flowers. It produces small, unremarkable flower spikes of no decorative value. Flowering exhausts it: once it has flowered, it stretches, goes bare at the base and declines. Cut the spikes off as soon as they appear.

These two habits noticeably extend its useful life, which remains of the order of one to two years. Plan to renew it: a 5 cm stem pushed into damp substrate roots within two to three weeks under glass.

Common problems

Foliage turning green again. Not enough light. This is problem number one with this plant.

Bare stem at the base, leaves only at the top. Not enough pruning, or flowering has been and gone. Cut it back hard: it will come again.

Soft, translucent leaves. Too much water — see Terrarium too humid.

Leaves drooping but still firm. Thirst. It reacts like fittonia, within a few hours, and lifts again once rehydrated — see Terrarium too dry.

Yellowing from the base. See Yellow leaves in a terrarium.

What to pair it with

With green, so the colour stands out: selaginella, a small fern, creeping fig, moss.

One tip on composition: a single strong point of colour per terrarium. Hypoestes or red fittonia, not both in a 20 cm jar — otherwise the eye no longer knows where to settle.

Our selection is on the tropical plants shelf, and Which plants for a terrarium gives the overview.

Sources

• Creating a Closed Terrarium — Penn State Extension
• How to Design a Closed-System Terrarium — Mississippi State University Extension