Cold hardiness & minimum temperature

Is Moss rose (Portulaca grandiflora)cold hardy? Hardiness zone & min temp

Also called moss rose, sun plant, portulaca, rose moss, eleven o'clock.

More about moss rose

About Moss rose

Portulaca grandiflora · also called moss rose, sun plant · flowering

Moss rose is a sun-loving, drought-tolerant South American annual grown for its jewel-bright single or double flowers in scarlet, yellow, orange, pink, white and bicolours above succulent needle-like foliage. It thrives in hot, dry conditions in poor soil and is ideal for sunny borders, rock gardens, containers and paving gaps. Listed by ASPCA as toxic to pets.

Cold limit: USDA 10-11 (grown as a warm-season annual in zones 2-9) · RHS H1c (21-35°C)

Watch for — Flowers failing to open: Flowers close in low light, overcast conditions and cool temperatures — if plants consistently fail to open check that they are receiving 6+ hours of direct sunlight daily.

What moss rose's hardiness rating actually means

Hardiness works differently for moss rose: 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-11 (grown as a warm-season annual in zones 2-9) — 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 moss rose 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 moss rose 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 moss rose can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Frost protection for borderline moss rose

Moss rose 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.

Moss rose hardiness — frequently asked questions

Is moss rose cold hardy?

Hardiness works differently for moss rose: 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. Moss rose is grown 10-11 (grown as a warm-season annual in zones 2-9); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature moss rose 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 moss rose?

Moss rose is rated USDA 10-11 (grown as a warm-season annual in zones 2-9) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can moss rose 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 moss rose 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.