Mature size & growth rate

How big does Black Spleenwort (Asplenium adiantum-nigrum) get?

Also called Black Spleenwort, Black Maidenhair Spleenwort.

More about black spleenwort

About Black Spleenwort

Asplenium adiantum-nigrum · also called Black Spleenwort, Black Maidenhair Spleenwort · houseplant

Asplenium adiantum-nigrum is a tough, evergreen fern native to the British Isles, much of Europe, western Asia, and parts of Africa, recognisable by its glossy, dark green, bipinnate-to-tripinnate fronds held on distinctively black-green stalks. It grows in rock crevices, shaded walls, and hedge banks on a range of substrates from near-neutral to mildly acidic. It is hardier and more adaptable than many wall ferns, tolerating light frost, periods of dryness, and varying pH, making it relatively easy to cultivate in a shaded rock garden or trough. It is not individually listed on the ASPCA database, so it is conservatively classified as mildly toxic.

Mature size: Up to 50 cm tall and 30–40 cm wide.

Indoor size vs how big it gets in the wild

Black Spleenwort grows into a room-scaled plant of roughly up to 50 cm tall and 30–40 cm wide. — bigger than a tabletop plant, but not a tree. Indoors and in a pot, expect up to 50 cm tall and 30–40 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 builds steadily in both height and spread to a medium, manageable size, filling a pot and a corner over a few years.

Growth rate and years to mature

Black Spleenwort 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: fertilising is rarely necessary; if growth is slow on very lean soil, apply a quarter-strength balanced liquid feed once in late spring.

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

How to keep black spleenwort smaller

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

Prune the tallest or longest growth back to a node to hold black spleenwort at the size you want.
Keep it slightly pot-bound and feed sparingly to cap the overall size.
Remove the largest or oldest leaves to keep the footprint in check.

How to grow black spleenwort bigger or faster

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

Brighter indirect light is the single biggest growth lever here.
Pot up a size every year or two while it is establishing.
Feed and water consistently through the growing season for steady, faster size gain.

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

When black spleenwort outgrows the room (or the pot)

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

It crowds the shelf or corner it lives in and starts leaning for light.
Roots circling the pot base or escaping the drainage holes.
It needs a noticeably bigger pot every year — a sign to pot up, divide, or prune.

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

Black Spleenwort size — frequently asked questions

How big does black spleenwort get?

Black Spleenwort reaches up to 50 cm tall and 30–40 cm wide. when grown indoors. It builds steadily in both height and spread to a medium, manageable size, filling a pot and a corner over a few years.

Is black spleenwort slow or fast growing?

Black Spleenwort is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Black Spleenwort grows into a room-scaled plant of roughly up to 50 cm tall and 30–40 cm wide. — bigger than a tabletop plant, but not a tree.

How long does black spleenwort 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 black spleenwort smaller?

Prune the tallest or longest growth back to a node to hold black spleenwort at the size you want. Keep it slightly pot-bound and feed sparingly to cap the overall size. Remove the largest or oldest leaves to keep the footprint in check.

How can I make black spleenwort grow bigger or faster?

Brighter indirect light is the single biggest growth lever here. Pot up a size every year or two while it is establishing. Feed and water consistently through the growing season for steady, faster size gain.