Mature size & growth rate

How big does Chilean Hard Fern (Blechnum chilense) get?

Also called Chilean Blechnum, Parablechnum chilense, Strap Fern.

More about chilean hard fern

About Chilean Hard Fern

Blechnum chilense · also called Chilean Blechnum, Parablechnum chilense · houseplant

Blechnum chilense is a bold, architectural fern native to Chile and Argentina, producing long, strap-like glossy fronds from a central crown. It is more cold-tolerant than most ferns and can be grown outdoors in mild UK climates. Prefers consistently moist, acidic soil and moderate indirect light. Generally considered safe for pets as a true fern.

Mature size: 60-120 cm tall, spreading to 80-100 cm wide

Indoor size vs how big it gets in the wild

Chilean Hard 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 60-120 cm tall, spreading to 80-100 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.

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

Chilean Hard 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: apply a diluted balanced liquid fertiliser at half strength once a month from spring to late summer. this fern is not a heavy feeder; over-fertilising causes lush but tender growth susceptible to frost. avoid feeding in autumn and winter.

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

How to keep chilean hard fern smaller

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

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

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

When chilean hard fern outgrows the room (or the pot)

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

Chilean Hard Fern size — frequently asked questions

How big does chilean hard fern get?

Chilean Hard Fern reaches 60-120 cm tall, spreading to 80-100 cm 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 chilean hard fern slow or fast growing?

Chilean Hard Fern is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Chilean Hard 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 chilean hard 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 chilean hard fern smaller?

Divide the clump every year or two — splitting chilean hard 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 chilean hard 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.