Mature size & growth rate

How big does Heart-leaved Blechnum (Blechnum cordatum) get?

Also called Heart-leaved Blechnum, Chilean Hard Fern.

More about heart-leaved blechnum

About Heart-leaved Blechnum

Blechnum cordatum · also called Heart-leaved Blechnum, Chilean Hard Fern · houseplant

Blechnum cordatum is a striking, large-growing hard fern from Chile and Argentina with broadly pinnate, deep-green fronds that can develop a short trunk over time. It appreciates cool to moderate temperatures, consistently moist soil, and high humidity, making it well-suited to cooler conservatories, shaded patios, or bright but cool indoor spaces.

Mature size: 60–120 cm tall, 80–120 cm wide at maturity

Watch for — Frond browning and dieback: Caused by heat stress, drought, or low humidity. This species prefers cooler conditions and suffers in warm, dry rooms. Move to a cooler position, maintain moisture, and raise humidity. Remove badly damaged fronds to encourage fresh growth.

Indoor size vs how big it gets in the wild

Heart-leaved Blechnum grows on a tree's timeline and scale — indoors it becomes a tall, trunked statement plant rather than a tabletop one. Indoors and in a pot, expect 60–120 cm tall, 80–120 cm wide at maturity. 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 gains real height on a trunk or main stem, adding a tier of leaves a year and eventually reaching for the ceiling — this is a plant you grow up, not out.

Growth rate and years to mature

Heart-leaved Blechnum 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 balanced, slow-release fertiliser at the start of the growing season, or use a liquid feed at half strength monthly from spring to early autumn. this species does not need heavy feeding; avoid high-nitrogen formulas that promote lush but weak growth susceptible to pests.

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

How to keep heart-leaved blechnum smaller

You are not stuck with the maximum size. For heart-leaved blechnum specifically, these are the levers, in order of impact:

The decisive tool is the secateurs: heart-leaved blechnum can be topped (cut the main growing tip) to cap its height and force a bushier, shorter shape.
Keeping it deliberately pot-bound in a snug container slows the whole plant and limits ultimate size.
Prune in spring so it heals fast; remove the tallest leader back to a node to reset the height.
Expect to top or hard-prune it every year or two — left alone it heads for the ceiling.

The keep-it-smaller method, step by step

Pick the new height. Decide how tall you want heart-leaved blechnum and find a leaf node or branch point just below that.
Top the main stem. Cut the main growing tip cleanly just above that node in spring; this permanently caps the height and forces side branches.
Keep the pot snug. Avoid jumping to a much bigger pot — a slightly restricted rootball keeps the whole plant smaller.
Maintain the shape. Prune back the tallest new leaders each spring to hold it at the height you chose.

How to grow heart-leaved blechnum bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for heart-leaved blechnum the accelerators are:

The biggest lever is light — a tree-type plant in dim light barely gains height; move it brighter.
Pot up a size every year or two while young; restricted roots are the main thing holding height back.
Feed regularly through the growing season and keep it warm — height comes from sustained good conditions.

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

When heart-leaved blechnum outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for heart-leaved blechnum:

The top leaves pressing against or bent by the ceiling — the classic "this is now too tall indoors" sign.
It has to be moved away from a light source it has literally outgrown.
Roots filling the largest pot you can reasonably keep indoors — at that point it is top-or-prune or move it outside (if hardy).

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

Heart-leaved Blechnum size — frequently asked questions

How big does heart-leaved blechnum get?

Heart-leaved Blechnum reaches 60–120 cm tall, 80–120 cm wide at maturity when grown indoors. It gains real height on a trunk or main stem, adding a tier of leaves a year and eventually reaching for the ceiling — this is a plant you grow up, not out.

Is heart-leaved blechnum slow or fast growing?

Heart-leaved Blechnum is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Heart-leaved Blechnum grows on a tree's timeline and scale — indoors it becomes a tall, trunked statement plant rather than a tabletop one.

How long does heart-leaved blechnum 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 heart-leaved blechnum smaller?

The decisive tool is the secateurs: heart-leaved blechnum can be topped (cut the main growing tip) to cap its height and force a bushier, shorter shape. Keeping it deliberately pot-bound in a snug container slows the whole plant and limits ultimate size. Prune in spring so it heals fast; remove the tallest leader back to a node to reset the height. Expect to top or hard-prune it every year or two — left alone it heads for the ceiling.

How can I make heart-leaved blechnum grow bigger or faster?

The biggest lever is light — a tree-type plant in dim light barely gains height; move it brighter. Pot up a size every year or two while young; restricted roots are the main thing holding height back. Feed regularly through the growing season and keep it warm — height comes from sustained good conditions.