Cold hardiness & minimum temperature

Is Purple Fountain Grass (Pennisetum setaceum 'Rubrum')cold hardy? Hardiness zone & min temp

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.

Cold limit: USDA 9-11 (grown as an annual or overwintered indoors in colder zones) · RHS H2 (10 to 35°C)

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.

What purple fountain grass's hardiness rating actually means

Hardiness works differently for purple fountain grass: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA 9-11 (grown as an annual or overwintered indoors in colder zones) — the zones where it can be left outdoors year-round.

New to these scales? The USDA hardiness zone map explained covers how the zone numbers work, and you can find your own zone with the zone finder.

Minimum temperature — and what happens below it

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

Concretely, for purple fountain grass as it gets too cold:

Light frost (around 0 to −2 °C) damages or kills tender summer crops outright; cold-hardy types take a few degrees of frost.
The plant does not "survive winter" — its life cycle simply ends, by design, when frost arrives or it finishes cropping.
A surprise late spring frost can also kill young transplants set out too early, before the season even starts.

Can purple fountain grass go outside or overwinter — and where?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost.
In short-season zones, start it indoors or under cover to stretch the effective growing window.
Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

Work back from your local frost dates with the frost-date calculator: the last spring frost and first autumn frost are what really decide when purple fountain grass can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline purple fountain grass

Purple Fountain Grass is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks.
Have row cover ready for an unexpected late spring or early autumn frost.
Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.

Purple Fountain Grass hardiness — frequently asked questions

Is purple fountain grass cold hardy?

Hardiness works differently for purple fountain grass: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". A seasonal crop, not a perennial. Purple Fountain Grass is grown 9-11 (grown as an annual or overwintered indoors in colder zones); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature purple fountain grass can survive?

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

What hardiness zone is purple fountain grass?

Purple Fountain Grass is rated USDA 9-11 (grown as an annual or overwintered indoors in colder zones) and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can purple fountain grass survive winter outside?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost. In short-season zones, start it indoors or under cover to stretch the effective growing window. Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

How do I protect purple fountain grass from frost?

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks. Have row cover ready for an unexpected late spring or early autumn frost. Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.