Cold hardiness & minimum temperature

Is Salsify (Tragopogon porrifolius)cold hardy? Hardiness zone & min temp

Also called Oyster plant, Vegetable oyster, Purple salsify.

More about salsify

About Salsify

Tragopogon porrifolius · also called Oyster plant, Vegetable oyster · edible

Salsify is a hardy biennial grown for its long, slender taproot with a delicate oyster-like flavour. Direct-sown like a carrot, it needs deep, stone-free soil and a full 120-150 day season. Roots sweeten after autumn frost and can overwinter in the ground. Its purple flowers open only in morning sun.

Cold limit: USDA 3-9 (roots overwinter in the ground in most zones) · RHS H5 (fully hardy; roots survive UK winters in situ) (15-21°C)

Watch for — Premature bolting: Sowing too early into cold soil, or a prolonged cold snap, can vernalise the biennial and trigger first-year flowering, which makes roots woody. Sow once soil has warmed.

What salsify's hardiness rating actually means

Hardiness works differently for salsify: 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 H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 3-9 (roots overwinter in the ground in most 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 salsify 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 salsify 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 salsify can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Frost protection for borderline salsify

Salsify 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.

Salsify hardiness — frequently asked questions

Is salsify cold hardy?

Hardiness works differently for salsify: 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. Salsify is grown as an annual in USDA 3-9 (roots overwinter in the ground in most zones); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature salsify 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 salsify?

Salsify is rated USDA 3-9 (roots overwinter in the ground in most zones) and RHS H5 — Hardy in most of the UK and in cold winters.

Can salsify 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 salsify 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.