Cold hardiness & minimum temperature

Is Sweet Annie (Artemisia annua)cold hardy? Hardiness zone & min temp

Also called sweet Annie, sweet wormwood, annual wormwood.

More about sweet annie

About Sweet Annie

Artemisia annua · also called sweet Annie, sweet wormwood · herb

Sweet Annie is a tall, fast-growing annual wormwood with fern-like, intensely sweet-scented foliage prized for fragrant wreaths and dried crafts. Its lacy green leaves release a distinctive aroma, and tiny yellow flowers appear in late summer. An easy, sun-loving plant for poor, free-draining soil, it self-seeds prolifically and can naturalise aggressively if flower heads are left to mature.

Cold limit: USDA Grown as a warm-season annual in zones 2-11; killed by frost · RHS H3 (15-30°C)

Watch for — Frost kill: Being a tender annual, it collapses with the first hard frost. Harvest foliage at peak fragrance before flowering, and resow from saved seed each spring.

What sweet annie's hardiness rating actually means

Hardiness works differently for sweet annie: 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 H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA Grown as a warm-season annual in zones 2-11; killed by frost — 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 sweet annie 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 sweet annie 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 sweet annie can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline sweet annie

Sweet Annie 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.

Sweet Annie hardiness — frequently asked questions

Is sweet annie cold hardy?

Hardiness works differently for sweet annie: 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. Sweet Annie is grown Grown as a warm-season annual in zones 2-11; killed by frost; you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature sweet annie 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 sweet annie?

Sweet Annie is rated USDA Grown as a warm-season annual in zones 2-11; killed by frost and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can sweet annie 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 sweet annie 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.