Mature size & growth rate

How big does Forked Spleenwort (Asplenium septentrionale) get?

Also called Forked Spleenwort, Northern Spleenwort, Grass Fern.

More about forked spleenwort

About Forked Spleenwort

Asplenium septentrionale · also called Forked Spleenwort, Northern Spleenwort · houseplant

Asplenium septentrionale is a small, distinctive, evergreen fern native to rocky mountain habitats across Europe (including the British Isles), Asia, and western North America, where it wedges itself into acidic rock crevices and cliff faces. Its highly unusual fronds consist of narrow, forked, grass-like segments on wiry dark stalks, making it look strikingly unlike a typical fern — a feature that earns it the nickname grass fern. It is an extremely slow-growing, drought-tolerant species that requires excellent drainage and partial shade; the single most critical care point is that it must never sit in wet, poorly drained soil. Its pet-toxicity status is not individually confirmed by ASPCA; a mildly-toxic precautionary classification is used.

Mature size: 5–20 cm tall and 10–30 cm wide.

Indoor size vs how big it gets in the wild

Forked Spleenwort is a naturally small plant — it stays shelf- and desk-sized for its whole life, so it never becomes a space problem. Indoors and in a pot, expect 5–20 cm tall and 10–30 cm wide.. A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

It grows mostly by adding leaves, offsets or a slightly wider rosette rather than gaining height — the footprint barely changes year to year.

Growth rate and years to mature

Forked Spleenwort 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: no feeding required; excess nutrients cause atypical, lush growth that is out of character and susceptible to disease in this naturally lean-growing species.

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

How to keep forked spleenwort smaller

Good news — forked spleenwort barely needs managing. If you do want to keep it tidy:

You rarely need to do anything: forked spleenwort is so slow that it can sit in the same small pot for years.
Keeping it slightly pot-bound and easing back on feed naturally caps the size.
Pinch or remove the oldest, tiredest leaves so energy goes into a compact, fresh-looking plant.

How to grow forked spleenwort bigger or faster

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

Move it to brighter (but not scorching) light — that is the single biggest growth lever for a small plant.
A small step up in pot size every couple of years gives the roots a little more room without triggering a size jump.
Feed lightly through the growing season; this plant simply will not race however hard you push it.

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

When forked spleenwort outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for forked spleenwort:

Roots circling the bottom or pushing out of the drainage hole — it wants a pot one size up, not a bigger room.
Offsets crowding the surface so the original plant looks squashed.
Honestly, forked spleenwort rarely outgrows a room — outgrowing its pot is the only realistic limit.

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

Forked Spleenwort size — frequently asked questions

How big does forked spleenwort get?

Forked Spleenwort reaches 5–20 cm tall and 10–30 cm wide. when grown indoors. It grows mostly by adding leaves, offsets or a slightly wider rosette rather than gaining height — the footprint barely changes year to year.

Is forked spleenwort slow or fast growing?

Forked Spleenwort 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. Forked Spleenwort is a naturally small plant — it stays shelf- and desk-sized for its whole life, so it never becomes a space problem.

How long does forked spleenwort 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 forked spleenwort smaller?

You rarely need to do anything: forked spleenwort is so slow that it can sit in the same small pot for years. Keeping it slightly pot-bound and easing back on feed naturally caps the size. Pinch or remove the oldest, tiredest leaves so energy goes into a compact, fresh-looking plant.

How can I make forked spleenwort grow bigger or faster?

Move it to brighter (but not scorching) light — that is the single biggest growth lever for a small plant. A small step up in pot size every couple of years gives the roots a little more room without triggering a size jump. Feed lightly through the growing season; this plant simply will not race however hard you push it.