Mature size & growth rate

How big does Emerald Spike Moss (Selaginella martensii) get?

Also called Martens' spikemoss, emerald spikemoss, variegated spikemoss, Martens club moss, frosty fern (when silver-tipped).

More about emerald spike moss

About Emerald Spike Moss

Selaginella martensii · also called Martens' spikemoss, emerald spikemoss · houseplant

Emerald spike moss (Selaginella martensii) is a compact, fern-like spikemoss with upright branching fronds, grown indoors for its delicate emerald foliage. It demands constant high humidity and evenly moist soil, so it thrives best in a terrarium. It is considered pet-safe under ASPCA standards for the Selaginella genus.

Mature size: Around 15-30 cm tall and a similar spread; stays small and bushy, ideal for terrariums.

Watch for — Leggy, thin, open growth: Insufficient light or very low humidity; improve both and pinch back to encourage a denser, bushier habit.

Indoor size vs how big it gets in the wild

Emerald Spike Moss does not get tall — it gets long. Size here is about stem length and how you train or cut it, not how much floor it claims. Indoors and in a pot, expect around 15-30 cm tall and a similar spread. In the ground with no restriction it is a completely different plant — stays small and bushy, ideal for terrariums. — which is why the pot, the light and the pruning matter so much for the size you actually end up with.

Growth shows up as lengthening stems that trail down or climb up a support; the plant can be kept tiny or grown metres long from the exact same root system.

Growth rate and years to mature

Emerald Spike Moss is a moderate grower. Realistically, expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Its feeding profile backs this up: feed lightly with a balanced liquid houseplant fertiliser diluted to half or quarter strength, roughly monthly during spring and summer. spikemosses are sensitive to fertiliser salts, so flush occasionally and stop feeding in autumn and winter.

Want this turned into the right next pot at the right moment? The pot size calculator and the emerald spike moss repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast emerald spike moss grows.

How to keep emerald spike moss smaller

You are not stuck with the maximum size. For emerald spike moss specifically, these are the levers, in order of impact:

Trim the longest vines back to the length you want — emerald spike moss takes hard cutting well and bushes out from the cut.
Cut just above a leaf node; each trimmed stem usually branches into two, so pruning makes it fuller, not sparser.
The cuttings root easily in water or mix, so "keeping it smaller" doubles as free new plants.
A trim once or twice a season is usually enough to hold its length.

The keep-it-smaller method, step by step

Decide the length you want. Pick the point each vine of emerald spike moss should stop — you can be aggressive; it regrows readily.
Cut just above a node. Snip about 0.5 cm above a leaf node so the stem branches there instead of dying back.
Root the cuttings. Drop the trimmed pieces in water or mix — they root in 2-4 weeks and can fill the same pot for a bushier look.
Repeat as it runs. Re-trim whenever it overshoots; regular light pruning keeps it both smaller and fuller.

How to grow emerald spike moss bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for emerald spike moss the accelerators are:

More (indirect) light dramatically lengthens the vines and enlarges the leaves.
Give it something to climb — many vines grow far faster and bigger up a support than trailing.
Feed through spring and summer and keep it consistently watered while it is actively running.

Light is almost always the ceiling. The emerald spike moss light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When emerald spike moss outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for emerald spike moss:

Vines pooling on the floor or wrapping past where you want them — purely a trimming cue, not a repot one.
Bare, leggy stems with leaves only at the tips (usually a light problem, not a size one).
A tangled mass that has outrun its support and needs cutting back and re-training.

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the emerald spike moss repotting guide. If you want more of this plant instead of a bigger one, the emerald spike moss propagation guide turns prunings into new plants.

Emerald Spike Moss size — frequently asked questions

How big does emerald spike moss get?

Emerald Spike Moss reaches around 15-30 cm tall and a similar spread when grown indoors, and far larger where it grows unrestricted (stays small and bushy, ideal for terrariums.). Growth shows up as lengthening stems that trail down or climb up a support; the plant can be kept tiny or grown metres long from the exact same root system.

Is emerald spike moss slow or fast growing?

Emerald Spike Moss is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Emerald Spike Moss does not get tall — it gets long. Size here is about stem length and how you train or cut it, not how much floor it claims.

How long does emerald spike moss take to reach full size?

Roughly three to six years to reach mature indoor size, gaining a steady amount each growing season. Light, pot size and feeding move that timeline more than anything else.

How do I keep emerald spike moss smaller?

Trim the longest vines back to the length you want — emerald spike moss takes hard cutting well and bushes out from the cut. Cut just above a leaf node; each trimmed stem usually branches into two, so pruning makes it fuller, not sparser. The cuttings root easily in water or mix, so "keeping it smaller" doubles as free new plants. A trim once or twice a season is usually enough to hold its length.

How can I make emerald spike moss grow bigger or faster?

More (indirect) light dramatically lengthens the vines and enlarges the leaves. Give it something to climb — many vines grow far faster and bigger up a support than trailing. Feed through spring and summer and keep it consistently watered while it is actively running.