Cold hardiness & minimum temperature

Is Glasswort (Salicornia europaea)cold hardy? Hardiness zone & min temp

Also called Glasswort, Common Glasswort, Marsh Samphire, Chicken Claws.

More about glasswort

About Glasswort

Salicornia europaea · also called Glasswort, Common Glasswort · edible

Salicornia europaea is a native annual halophyte of European and North American saltmarshes and mudflats, producing distinctive fleshy, jointed, leafless green stems that turn red-purple in autumn. It demands full sun and highly saline, moist to waterlogged soil — mimicking tidal saltmarsh conditions is essential. The single most important care fact is that it cannot tolerate low-salinity soil; brackish or salt-amended growing media is non-negotiable. Salicornia is not listed on the ASPCA Toxic Plant database, but its very high salt content may cause gastrointestinal upset in pets if eaten in quantity; treat as mildly toxic as a precaution.

Cold limit: USDA 3-9 (grown as annual) · RHS H6 (5-30°C)

What glasswort's hardiness rating actually means

Hardiness works differently for glasswort: 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 H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 3-9 (grown as annual) — 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 glasswort 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 glasswort 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 glasswort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Frost protection for borderline glasswort

Glasswort 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.

Glasswort hardiness — frequently asked questions

Is glasswort cold hardy?

Hardiness works differently for glasswort: 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. Glasswort is grown 3-9 (grown as annual); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature glasswort 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 glasswort?

Glasswort is rated USDA 3-9 (grown as annual) and RHS H6 — Hardy throughout the UK and northern Europe.

Can glasswort 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 glasswort 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.