Mature size & growth rate

How big does Boston fern (Nephrolepis exaltata) get?

Also called sword fern, Boston sword fern.

About Boston fern

Nephrolepis exaltata · also called sword fern, Boston sword fern · tropical

Boston fern is a classic trailing fern that has been a houseplant since Victorian times. Indoors it demands high humidity and steady moisture; in dry centrally heated rooms it sheds fronds quickly. Pet-safe by ASPCA standards.

Nephrolepis exaltata is a pantropical sword fern (Florida, the West Indies, Central and South America, Polynesia and Africa); the Boston fern is a natural variant found in an 1894 shipment of ferns from Philadelphia to Boston.

An evergreen fern with an upright-spreading habit to about 3 ft tall and wide; fronds start upright and arch gracefully with age — it needs high humidity and benefits from a tray of wet pebbles indoors.

Mature size: 60-90 cm tall and wide

Sources: missouribotanicalgarden.org, hort.extension.wisc.edu

Indoor size vs how big it gets in the wild

Boston 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 60-90 cm tall and 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.

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

Boston 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: quarter-strength balanced feed every 4 weeks during the growing season; ferns are sensitive to over-feeding.

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

How to keep boston fern smaller

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

Divide the clump every year or two — splitting boston 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 boston 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 boston fern bigger or faster

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

When boston fern outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for boston 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 boston fern repotting guide. If you want more of this plant instead of a bigger one, the boston fern propagation guide turns prunings into new plants.

Boston fern size — frequently asked questions

How big does boston fern get?

Boston fern reaches 60-90 cm tall and wide when grown indoors. 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 boston fern slow or fast growing?

Boston fern is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Boston 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 boston 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 boston fern smaller?

Divide the clump every year or two — splitting boston 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 boston 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.