Mature size & growth rate

How big does Giant Montbretia (Crocosmia masonorum) get?

Also called Mason's Crocosmia, Giant Crocosmia, Falling Stars.

More about giant montbretia

About Giant Montbretia

Crocosmia masonorum · also called Mason's Crocosmia, Giant Crocosmia · flowering

Giant Montbretia is a vigorous South African cormous perennial with bold pleated foliage and arching sprays of vivid orange-red flowers in mid-summer. One of the largest crocosmia species, it makes a striking architectural clump in borders. Grows best in full sun with well-drained soil. Treat as mildly toxic around pets.

Mature size: 90-150 cm tall in flower

Indoor size vs how big it gets in the wild

Giant Montbretia 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 90-150 cm tall in flower. 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

Giant Montbretia is a fast grower. Realistically, expect two to four years from a young plant to a room-filling specimen in good light. Its feeding profile backs this up: feed with a general balanced fertiliser in spring when new growth appears. a high-potash liquid feed applied monthly through summer encourages flowering and corm health.

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

How to keep giant montbretia smaller

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

Divide the clump every year or two — splitting giant montbretia 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 giant montbretia 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 giant montbretia bigger or faster

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

When giant montbretia outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for giant montbretia:

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

Giant Montbretia size — frequently asked questions

How big does giant montbretia get?

Giant Montbretia reaches 90-150 cm tall in flower 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 giant montbretia slow or fast growing?

Giant Montbretia is a fast grower. Expect two to four years from a young plant to a room-filling specimen in good light. Giant Montbretia 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 giant montbretia take to reach full size?

Roughly two to four years from a young plant to a room-filling specimen in good light. Light, pot size and feeding move that timeline more than anything else.

How do I keep giant montbretia smaller?

Divide the clump every year or two — splitting giant montbretia 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 giant montbretia 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.