Selaginella gives the finest texture you can get in a terrarium: a dense carpet of light-green lace that immediately suggests a woodland floor. It is also the most demanding plant in the usual selection — it needs high and constant humidity, and browns within a few hours of dry air. In a closed terrarium that seals properly, it is easy; anywhere else, it fails.

Identity card

What it brings

Scale. Its finely cut shoots are so small that they make the rest of the composition look larger: next to a selaginella, a 20 cm jar looks like a woodland floor. It is one of the few plants that produce that miniature effect without any trick.

It also covers the ground quickly, spreading by shoots that root where they touch. It works well alongside moss, with which it forms two very different layers of green.

Humidity: the critical point

This is the whole story with this plant. Selaginella has no thick cuticle to hold its water: it lives in the saturated air of the forest floor. In a heated room, it browns within a day.

What it needs: a closed terrarium whose stopper or lid really seals, with mist that comes back every morning. If the mist disappears for any length of time, it is the first to show it — before the fittonia, before the moss.

The browning always starts at the tips of the shoots. That is a very useful early signal: correct it as soon as you see it, following Terrarium too dry.

Light

Partial shade to bright indirect light. It tolerates less light than most of its neighbours, which makes it a good candidate for a terrarium placed away from the window.

Never direct sun, which scorches it very quickly — see Terrarium too hot.

Substrate and planting

An airy terrarium substrate that holds moisture: coir, a little fine bark, a touch of sphagnum if you have some.

Rinse the root ball in lukewarm water, spread the clump out rather than pushing it in, and press lightly to make contact. Mist straight afterwards: this is the plant you must not let dry out, even for an hour, between leaving the pot and the closing of the terrarium.

Care

Almost nothing. It spreads by itself and makes do with the water circulating in the terrarium. Only two things to do:

• Keep the spread in check: it can cover smaller plants. Cut the excess shoots with scissors; they do not regrow from the cut, but the clump thickens.
• Remove the browned parts, which will not green up again and would feed moulds in a closed environment.

Common problems

Brown, dry tips. Air too dry. This is the most frequent case and the quickest to correct.

Soft clump, brown at the base, soaked substrate. Too much water and roots starved of air — see Terrarium too humid.

Green that pales without browning. Too little light, or water that is too hard.

White veil at the base. Mould on dead matter caught in the clump: remove the debris, air it out, see Mould in a closed terrarium.

What to pair it with

It gets on with anything that likes humidity: fittonia, Ficus pumila, peperomia, a small fern, mosses.

It is incompatible with succulents, without exception — their needs are opposites. See Closed or open terrarium.

Our selection is in the tropical plants section.

Sources

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