Mature size & growth rate

How big does Walking Fern (Asplenium rhizophyllum) get?

Also called Walking Fern, Walking Spleenwort.

More about walking fern

About Walking Fern

Asplenium rhizophyllum · also called Walking Fern, Walking Spleenwort · houseplant

Walking fern is a small evergreen spleenwort with long, tapering, arrow-shaped fronds that root where their tips touch soil, forming new plantlets that appear to walk across the ground. Native to shaded limestone rocks in eastern North America, it thrives in cool, humid, low-light terrariums on moist, alkaline, gritty substrate and stays under 15 cm tall.

Mature size: Fronds 10-30 cm long; the plant stays under 15 cm tall but a colony spreads steadily sideways via tip-rooting.

Indoor size vs how big it gets in the wild

Walking Fern stays fairly low but widens over time — it spreads into a bigger clump by offsets, runners or rhizomes rather than shooting upward. Indoors and in a pot, expect fronds 10-30 cm long. In the ground with no restriction it is a completely different plant — the plant stays under 15 cm tall but a colony spreads steadily sideways via tip-rooting. — which is why the pot, the light and the pruning matter so much for the size you actually end up with.

Size here is about width, not height: the plant builds an ever-wider clump or sends out plantlets and runners while staying relatively short.

Growth rate and years to mature

Walking Fern 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 sparingly, no more than every 6-8 weeks in spring and summer with a quarter-strength balanced liquid fertiliser. this low-nutrient rock dweller is easily burned, so under-feed rather than over-feed.

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

How to keep walking fern smaller

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

Divide the clump every year or two — splitting walking fern is the main way to control its spread and refresh it.
Remove runners, plantlets or offsets as they appear if you want it to stay a single tight clump.
Keep it slightly pot-bound; a snug pot naturally limits how wide the clump can get.

The keep-it-smaller method, step by step

Lift the whole plant. Slide walking fern out of its pot in spring when the clump has filled it.
Split the clump. Tease or cut the rootball into two or more sections, each with healthy roots and growth.
Repot one division. Put a single division back in the original pot to reset it to a smaller size; pot or give away the rest.
Remove offsets as they form. Through the year, detach new runners or pups to stop it spreading again.

How to grow walking fern bigger or faster

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

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger.
Brighter light speeds up clump and offset production noticeably.
Leave plantlets and offsets attached and feed through the growing season for the fastest spread.

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

When walking fern outgrows the room (or the pot)

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

The clump bulging over the pot rim or splitting the pot — the cue to divide, not to find a bigger room.
A dense centre that goes bare or tired while the edges keep spreading.
Runners or offsets escaping across the shelf or into neighbouring pots.

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

Walking Fern size — frequently asked questions

How big does walking fern get?

Walking Fern reaches fronds 10-30 cm long when grown indoors, and far larger where it grows unrestricted (the plant stays under 15 cm tall but a colony spreads steadily sideways via tip-rooting.). Size here is about width, not height: the plant builds an ever-wider clump or sends out plantlets and runners while staying relatively short.

Is walking fern slow or fast growing?

Walking Fern is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Walking Fern stays fairly low but widens over time — it spreads into a bigger clump by offsets, runners or rhizomes rather than shooting upward.

How long does walking fern 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 walking fern smaller?

Divide the clump every year or two — splitting walking fern is the main way to control its spread and refresh it. Remove runners, plantlets or offsets as they appear if you want it to stay a single tight clump. Keep it slightly pot-bound; a snug pot naturally limits how wide the clump can get.

How can I make walking fern grow bigger or faster?

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger. Brighter light speeds up clump and offset production noticeably. Leave plantlets and offsets attached and feed through the growing season for the fastest spread.