Mature size & growth rate

How big does Canary Reed Grass (Phalaris arundinacea) get?

Also called Reed Canary Grass, Ribbon Grass, Gardener's Garters.

More about canary reed grass

About Canary Reed Grass

Phalaris arundinacea · also called Reed Canary Grass, Ribbon Grass · flowering

Canary Reed Grass is a vigorous, rhizomatous wetland grass with broad, strappy leaves that can be variegated in cultivated forms (Phalaris arundinacea var. picta 'Gardener's Garters'). It thrives at pond margins and in wet soils but spreads aggressively by creeping rhizomes, making containment essential in garden settings. Listed as a noxious weed in some US states. Generally considered low toxicity but may cause mild issues in livestock.

Mature size: 90-180 cm tall; spread indefinite without containment

Watch for — Aggressive spreading: The primary management challenge. Spreads rapidly by deep rhizomes. Plant in buried containers at pond margins or install physical rhizome barriers 45-60 cm deep in borders.

Indoor size vs how big it gets in the wild

Canary Reed Grass 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 90-180 cm tall. In the ground with no restriction it is a completely different plant — spread indefinite without containment — which is why the pot, the light and the pruning matter so much for the size you actually end up with.

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

Canary Reed Grass 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: fertilising in most garden settings is unnecessary and increases invasive vigour. in very poor soils a light balanced feed in spring may improve the ornamental display. avoid rich feeding at pond margins where eutrophication is a concern.

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

How to keep canary reed grass smaller

You are not stuck with the maximum size. For canary reed grass specifically, these are the levers, in order of impact:

Divide the clump every year or two — splitting canary reed grass 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 canary reed grass 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 canary reed grass bigger or faster

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

When canary reed grass outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for canary reed grass:

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

Canary Reed Grass size — frequently asked questions

How big does canary reed grass get?

Canary Reed Grass reaches 90-180 cm tall when grown indoors, and far larger where it grows unrestricted (spread indefinite without containment). 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 canary reed grass slow or fast growing?

Canary Reed Grass is a fast grower. Expect two to four years from a young plant to a room-filling specimen in good light. Canary Reed Grass 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 canary reed grass 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 canary reed grass smaller?

Divide the clump every year or two — splitting canary reed grass 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 canary reed grass 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.