Mature size & growth rate

How big does Crocosmia masoniorum (Crocosmia masoniorum) get?

Also called giant montbretia, Mason's crocosmia.

More about crocosmia masoniorum

About Crocosmia masoniorum

Crocosmia masoniorum · also called giant montbretia, Mason's crocosmia · flowering

Crocosmia masoniorum, the giant montbretia, is a robust South African species bearing horizontally arching stems of upward-facing flame-orange flowers above broad, strongly pleated sword-shaped leaves in mid to late summer. An RHS Award of Garden Merit perennial, it forms bold clumps in sunny borders, tolerates coastal sites, and is excellent for cutting and for pollinators.

Mature size: About 100-120 cm tall and 60-90 cm wide, spreading by corms.

Indoor size vs how big it gets in the wild

Crocosmia masoniorum 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 about 100-120 cm tall and 60-90 cm wide, spreading by corms.. 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

Crocosmia masoniorum 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: feed with a balanced fertiliser in spring and a potash-rich feed as flower stems emerge; mulch in spring to feed the corms and conserve moisture through summer.

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

How to keep crocosmia masoniorum smaller

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

Divide the clump every year or two — splitting crocosmia masoniorum 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 crocosmia masoniorum 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 crocosmia masoniorum bigger or faster

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

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger.
Good light plus regular feeding maximises offset and runner production.
Leave plantlets and offsets attached and feed through the growing season for the fastest spread.

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

When crocosmia masoniorum outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for crocosmia masoniorum:

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 crocosmia masoniorum repotting guide. If you want more of this plant instead of a bigger one, the crocosmia masoniorum propagation guide turns prunings into new plants.

Crocosmia masoniorum size — frequently asked questions

How big does crocosmia masoniorum get?

Crocosmia masoniorum reaches about 100-120 cm tall and 60-90 cm wide, spreading by corms. 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 crocosmia masoniorum slow or fast growing?

Crocosmia masoniorum is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Crocosmia masoniorum 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 crocosmia masoniorum 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 crocosmia masoniorum smaller?

Divide the clump every year or two — splitting crocosmia masoniorum 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 crocosmia masoniorum grow bigger or faster?

Give it a wider pot and let the clump fill it — width is exactly how this plant gets bigger. Good light plus regular feeding maximises offset and runner production. Leave plantlets and offsets attached and feed through the growing season for the fastest spread.