Cold hardiness & minimum temperature

Is Stinking Iris (Iris foetidissima)cold hardy? Hardiness zone & min temp

Also called Stinking Iris, Roast Beef Plant, Gladdon, Gladwin Iris.

More about stinking iris

About Stinking Iris

Iris foetidissima · also called Stinking Iris, Roast Beef Plant · flowering

Stinking Iris is a versatile, shade-tolerant evergreen perennial grown as much for its spectacular orange-red seed pods — which split open in autumn and persist through winter — as its muted purple-lilac summer flowers. Highly adaptable to dry shade, chalk, and clay, it is one of the most unfussy irises for difficult garden spots. Hardy USDA zones 6–9.

Cold limit: USDA 6-9 · RHS H6 (-20°C to 30°C; leaves may be damaged below -10°C)

Watch for — Leaf cold damage: Evergreen leaves can be browned or killed by cold winds and temperatures below -10°C in exposed positions. Plants recover from rootstock in spring. Provide a sheltered spot or winter mulch in colder end of its range (zone 6).

What stinking iris's hardiness rating actually means

Yes — stinking iris is genuinely cold hardy. Rated RHS H6 and USDA 6-9, 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 6-9 — 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. Stinking Iris is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for stinking iris 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 stinking iris go outside or overwinter — and where?

Plant it out within USDA 6-9 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 stinking iris can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Stinking Iris hardiness — frequently asked questions

Is stinking iris cold hardy?

Yes — stinking iris is genuinely cold hardy. Rated RHS H6 and USDA 6-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Stinking Iris is hardy across USDA 6-9; 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 stinking iris can survive?

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

What hardiness zone is stinking iris?

Stinking Iris is rated USDA 6-9 and RHS H6 — Hardy throughout the UK and northern Europe.

Can stinking iris survive winter outside?

Plant it out within USDA 6-9 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 stinking iris 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.