Cold hardiness & minimum temperature

Is Hogweed (Heracleum sphondylium)cold hardy? Hardiness zone & min temp

Also called Hogweed, Common Hogweed, Cow Parsnip, Keck.

More about hogweed

About Hogweed

Heracleum sphondylium · also called Hogweed, Common Hogweed · flowering

Heracleum sphondylium is a robust native biennial or short-lived perennial of European hedgerows, roadsides, and rough grassland, thriving in moist, fertile soils in sun or partial shade. It forms dramatic flat-topped white umbels up to 15 cm across and can reach 2 m in height. The single most important care fact is that its sap contains furanocoumarins that cause phytophotodermatitis — severe blistering when sap-covered skin is exposed to sunlight — so always wear gloves when handling. The plant is considered mildly toxic to cats and dogs due to its phototoxic furanocoumarin content.

Cold limit: USDA 4-9 · RHS H6 (-20 to 25 °C)

What hogweed's hardiness rating actually means

Yes — hogweed 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. Hogweed is built for winter — once established it takes hard frost and snow in its stride.

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

Hogweed hardiness — frequently asked questions

Is hogweed cold hardy?

Yes — hogweed 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. Hogweed 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 hogweed can survive?

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

What hardiness zone is hogweed?

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

Can hogweed 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 hogweed 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.