Cold hardiness & minimum temperature

Is Iris 'Immortality' (Iris 'Immortality')cold hardy? Hardiness zone & min temp

Also called Immortality iris, white reblooming iris, rebloomer iris.

More about iris 'immortality'

About Iris 'Immortality'

Iris 'Immortality' · also called Immortality iris, white reblooming iris · flowering

Iris 'Immortality' is a reblooming tall bearded iris with pure ruffled white flowers and pale lemon beards, flowering in late spring and often again in late summer or autumn. Grow in full sun and sharply drained soil with rhizomes near the surface. Reaching about 75 cm, it is fragrant and reliably repeat-blooming in warm regions.

Cold limit: USDA 3-9 · RHS H7 (-29 to 30°C)

Watch for — Failure to rebloom: Cold climates, shade, crowding or under-feeding prevent the second flush. Site in full sun, feed through summer and divide regularly to encourage rebloom.

What iris 'immortality''s hardiness rating actually means

Yes — iris 'immortality' is genuinely cold hardy. Rated RHS H7 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H7 means: Hardy in the severest European continental winters. On the US scale that maps to USDA 3-9 — 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 below about −20 °C. Iris 'Immortality' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for iris 'immortality' as it gets too cold:

It tolerates winter lows to about −20 °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 iris 'immortality' go outside or overwinter — and where?

Plant it out within USDA 3-9 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 iris 'immortality' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Iris 'Immortality' hardiness — frequently asked questions

Is iris 'immortality' cold hardy?

Yes — iris 'immortality' is genuinely cold hardy. Rated RHS H7 and USDA 3-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Iris 'Immortality' is hardy across USDA 3-9; 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 iris 'immortality' can survive?

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

What hardiness zone is iris 'immortality'?

Iris 'Immortality' is rated USDA 3-9 and RHS H7 — Hardy in the severest European continental winters.

Can iris 'immortality' survive winter outside?

Plant it out within USDA 3-9 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 iris 'immortality' below its minimum temperature?

It tolerates winter lows to about −20 °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.