Mature size & growth rate

How big does Metallic Blue Fern (Microsorum thailandicum) get?

Also called Blue Elf Fern, Metallic Blue Fern, Thailand Blue Fern.

More about metallic blue fern

About Metallic Blue Fern

Microsorum thailandicum · also called Blue Elf Fern, Metallic Blue Fern · houseplant

Metallic blue fern is a striking tropical epiphyte from Thailand whose strap-shaped, leathery fronds shimmer with an iridescent blue-green sheen, brightest in low light. A slow-growing creeping-rhizome species, it loves warmth, very high humidity and bright shade, making it a prized terrarium and vivarium plant that reaches around 20-30 cm tall.

Mature size: Fronds typically 20-40 cm long; the plant stays around 20-30 cm tall while the rhizome creeps slowly sideways.

Watch for — Loss of blue iridescence: Too much light fades the metallic colour to green. Move to a shadier position to restore the signature blue sheen.

Indoor size vs how big it gets in the wild

Metallic Blue Fern 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 fronds typically 20-40 cm long. In the ground with no restriction it is a completely different plant — the plant stays around 20-30 cm tall while the rhizome creeps slowly sideways. — 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

Metallic Blue Fern is a slow grower. Realistically, expect many years — it gains very little each season, so it can hold the same shelf-sized footprint for 5-10+ years. Its feeding profile backs this up: feed very lightly every 4-6 weeks in the growing season with a quarter- to half-strength balanced liquid fertiliser, or mist on a dilute foliar feed. this slow grower is sensitive to fertiliser salts, so dilute heavily.

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

How to keep metallic blue fern smaller

You are not stuck with the maximum size. For metallic blue fern specifically, these are the levers, in order of impact:

Trim the longest vines back to the length you want — metallic blue fern 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 metallic blue fern 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 metallic blue fern bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for metallic blue fern 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 metallic blue fern light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When metallic blue fern outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for metallic blue fern:

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 metallic blue fern repotting guide. If you want more of this plant instead of a bigger one, the metallic blue fern propagation guide turns prunings into new plants.

Metallic Blue Fern size — frequently asked questions

How big does metallic blue fern get?

Metallic Blue Fern reaches fronds typically 20-40 cm long when grown indoors, and far larger where it grows unrestricted (the plant stays around 20-30 cm tall while the rhizome creeps slowly sideways.). 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 metallic blue fern slow or fast growing?

Metallic Blue Fern is a slow grower. Expect many years — it gains very little each season, so it can hold the same shelf-sized footprint for 5-10+ years. Metallic Blue Fern 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 metallic blue fern take to reach full size?

Roughly many years — it gains very little each season, so it can hold the same shelf-sized footprint for 5-10+ years. Light, pot size and feeding move that timeline more than anything else.

How do I keep metallic blue fern smaller?

Trim the longest vines back to the length you want — metallic blue fern 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 metallic blue fern 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.