Cold hardiness & minimum temperature

Is Skirret (Sium sisarum)cold hardy? Hardiness zone & min temp

Also called skirret, crummock, sweet water-parsnip.

More about skirret

About Skirret

Sium sisarum · also called skirret, crummock · edible

Skirret (Sium sisarum) is a hardy perennial root vegetable in the carrot family, once a staple before the potato. Each crown produces a cluster of slender, sweet white roots with a flavour between parsnip and sweet potato, best lifted after autumn frosts. It bears umbels of small white flowers and is grown for its tasty, fiddly-to-clean fingered roots.

Cold limit: USDA 4-9 · RHS H6 (10-24°C)

Watch for — Woody root core: Older roots and drought-grown plants develop a tough, stringy central core. Lift first- or second-year roots after frost and keep soil moist for tender flesh.

What skirret's hardiness rating actually means

Yes — skirret is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H6 means: Hardy throughout the UK and northern Europe. On the US scale that maps to USDA 4-9 — 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

Minimum survivable temperature is roughly about −20 to −15 °C. Skirret is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for skirret as it gets too cold:

It tolerates winter lows to about −20 to −15 °C once established.
Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root.
First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.

Can skirret go outside or overwinter — and where?

Plant it out within USDA 4-9 and it overwinters with little or no help.
It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy.
The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

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 skirret can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Skirret hardiness — frequently asked questions

Is skirret cold hardy?

Yes — skirret is genuinely cold hardy. Rated RHS H6 and USDA 4-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Skirret is hardy across USDA 4-9; it belongs in the ground or a frost-proof container, not on a windowsill, and many types actively need a cold winter to perform.

What is the minimum temperature skirret can survive?

Minimum survivable temperature is roughly about −20 to −15 °C. Skirret is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is skirret?

Skirret is rated USDA 4-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can skirret survive winter outside?

Plant it out within USDA 4-9 and it overwinters with little or no help. It does not want to come indoors — a warm winter room actually weakens a hardy plant by denying it dormancy. The real risks in its range are waterlogging, wind-rock on young plants, and a late hard frost on new growth — not ordinary winter cold.

What happens to skirret below its minimum temperature?

It tolerates winter lows to about −20 to −15 °C once established. Below its rated zone, the visible damage is browned or blackened top growth and, in the worst case, a killed crown or root. First-year, newly planted, or container-grown specimens are noticeably less hardy than established garden plants — the roots are exposed.