Mature size & growth rate

How big does Japanese Blood Grass (Imperata cylindrica 'Rubra') get?

Also called japanese blood grass, red baron blood grass.

More about japanese blood grass

About Japanese Blood Grass

Imperata cylindrica 'Rubra' · also called japanese blood grass, red baron blood grass · flowering

Imperata cylindrica 'Rubra', Japanese blood grass, is an upright ornamental grass with green blades whose upper halves turn blood-red, glowing translucent when backlit. The colour deepens through summer into autumn. It prefers full sun to part shade and moist, well-drained soil. Note its parent species is an invasive noxious weed, so plant the ornamental form responsibly and watch for green reversions.

Mature size: 30-50 cm tall and 30-45 cm wide, spreading gradually by rhizomes.

Watch for — Slow spring emergence: Blood grass is late to break dormancy and dies back in winter; do not assume it has died, and cut back old foliage in late winter.

Indoor size vs how big it gets in the wild

Japanese Blood 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 30-50 cm tall and 30-45 cm wide, spreading gradually by rhizomes.. 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

Japanese Blood Grass 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 lightly in spring with a balanced slow-release fertiliser if soil is poor. avoid heavy nitrogen, which encourages vigorous green growth and may promote unwanted green reversions.

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

How to keep japanese blood grass smaller

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

Divide the clump every year or two — splitting japanese blood 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 japanese blood 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 japanese blood grass bigger or faster

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

When japanese blood grass outgrows the room (or the pot)

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

Japanese Blood Grass size — frequently asked questions

How big does japanese blood grass get?

Japanese Blood Grass reaches 30-50 cm tall and 30-45 cm wide, spreading gradually by rhizomes. 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 japanese blood grass slow or fast growing?

Japanese Blood Grass is a moderate grower. Expect three to six years to reach mature indoor size, gaining a steady amount each growing season. Japanese Blood 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 japanese blood grass 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 japanese blood grass smaller?

Divide the clump every year or two — splitting japanese blood 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 japanese blood 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.