Mature size & growth rate

How big does Purple Fountain Grass (Pennisetum setaceum 'Rubrum') get?

Also called purple fountain grass, red fountain grass.

More about purple fountain grass

About Purple Fountain Grass

Pennisetum setaceum 'Rubrum' · also called purple fountain grass, red fountain grass · flowering

Purple fountain grass is a tender ornamental grass with burgundy-red foliage and arching, foxtail-like purple plumes from summer to frost. It forms a graceful fountain-shaped mound and is grown as an annual or container specimen in cold climates, overwintered only where frost is absent. Heat-loving and sun-hungry, it adds rich colour and movement.

Mature size: 0.9-1.2 m tall and 0.6-0.9 m wide.

Watch for — Frost death: Even a light frost kills the top growth and the plant rarely survives cold winters; lift and overwinter indoors or treat as an annual.

Indoor size vs how big it gets in the wild

Purple Fountain Grass reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back. Indoors and in a pot, expect 0.9-1.2 m tall and 0.6-0.9 m wide.. 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 sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Growth rate and years to mature

Purple Fountain Grass is a moderate grower. Realistically, expect a single growing season — it reaches full size in one year, then is done. Its feeding profile backs this up: feed lightly but regularly when grown in containers, every few weeks through summer with a balanced liquid feed, since potting mix is quickly depleted. in-ground plants need only a light spring feed.

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

How to keep purple fountain grass smaller

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

Choose a compact or dwarf variety of purple fountain grass from the start — that is the most reliable size control for an annual.
Grow it in a smaller container to naturally limit how large it gets.
For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier.
Sow a little later or space plants closer if you specifically want smaller individual plants.

How to grow purple fountain grass bigger or faster

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

Full sun, warm soil and steady water are what drive a crop to full size fastest.
Sow at the right time for your zone so it gets the whole season to size up.
Feed appropriately for the crop and never let it check (stall) from drought or cold.

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

When purple fountain grass outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for purple fountain grass:

It sprawls beyond its bed or container before harvest — usually a spacing or support issue.
It flops or needs staking once it hits full height.
Once it has fruited or bolted, it is at its final size for good — the next plant is a new sowing.

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

Purple Fountain Grass size — frequently asked questions

How big does purple fountain grass get?

Purple Fountain Grass reaches 0.9-1.2 m tall and 0.6-0.9 m wide. when grown indoors. It sizes up fast and once, racing from seedling to full size in a single season; after cropping it is finished, so size is a within-season question.

Is purple fountain grass slow or fast growing?

Purple Fountain Grass is a moderate grower. Expect a single growing season — it reaches full size in one year, then is done. Purple Fountain Grass reaches its full size within one growing season — there is no "long-term" size, just how big it gets before you harvest or it dies back.

How long does purple fountain grass take to reach full size?

Roughly a single growing season — it reaches full size in one year, then is done. Light, pot size and feeding move that timeline more than anything else.

How do I keep purple fountain grass smaller?

Choose a compact or dwarf variety of purple fountain grass from the start — that is the most reliable size control for an annual. Grow it in a smaller container to naturally limit how large it gets. For some crops, pinching or pruning the growing tips keeps the plant shorter and bushier. Sow a little later or space plants closer if you specifically want smaller individual plants.

How can I make purple fountain grass grow bigger or faster?

Full sun, warm soil and steady water are what drive a crop to full size fastest. Sow at the right time for your zone so it gets the whole season to size up. Feed appropriately for the crop and never let it check (stall) from drought or cold.