Cold hardiness & minimum temperature

Is Red Horned Poppy (Glaucium corniculatum)cold hardy? Hardiness zone & min temp

Also called Red horned poppy, Rough hornpoppy.

More about red horned poppy

About Red Horned Poppy

Glaucium corniculatum · also called Red horned poppy, Rough hornpoppy · flowering

Glaucium corniculatum is an annual or biennial native to the Mediterranean basin, south-western Asia, and the Middle East, growing on disturbed sandy and stony ground, roadsides, and field margins. It produces handsome rosettes of slightly hairy, blue-grey pinnate leaves and vivid crimson-red to orange flowers, each petal typically bearing a distinctive dark basal blotch. Like all Glaucium species it demands full sun, sharply drained poor soil, and abhors root disturbance; it is hardier than many sources suggest and excellent for gravel gardens. All parts are toxic to cats and dogs due to isoquinoline alkaloids.

Cold limit: USDA 6-10 · RHS H6 (-20°C to 35°C)

Watch for — Damping off and crown rot: Seedlings and young rosettes collapse at the base if sown or planted into wet, cold, or poorly aerated soil — always use free-draining compost with added grit and avoid overhead watering.

What red horned poppy's hardiness rating actually means

Yes — red horned poppy is genuinely cold hardy. Rated RHS H6 and USDA 6-10, 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 6-10 — 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. Red Horned Poppy is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for red horned poppy 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 red horned poppy go outside or overwinter — and where?

Plant it out within USDA 6-10 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 red horned poppy can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Red Horned Poppy hardiness — frequently asked questions

Is red horned poppy cold hardy?

Yes — red horned poppy is genuinely cold hardy. Rated RHS H6 and USDA 6-10, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Red Horned Poppy is hardy across USDA 6-10; 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 red horned poppy can survive?

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

What hardiness zone is red horned poppy?

Red Horned Poppy is rated USDA 6-10 and RHS H6 — Hardy throughout the UK and northern Europe.

Can red horned poppy survive winter outside?

Plant it out within USDA 6-10 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 red horned poppy 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.