Cold hardiness & minimum temperature

Is Cobra Lily (Arisaema sikokianum)cold hardy? Hardiness zone & min temp

Also called Japanese cobra lily, Sikoku jack-in-the-pulpit.

More about cobra lily

About Cobra Lily

Arisaema sikokianum · also called Japanese cobra lily, Sikoku jack-in-the-pulpit · flowering

Arisaema sikokianum is a prized Japanese woodland perennial, famed for its dramatic flower: a dark purple-brown striped spathe opening to reveal a pure-white, club-shaped spadix that glows in shade. Often paired with silver-marbled leaves, it grows from a corm in cool, moist, humus-rich soil and dies back each winter.

Cold limit: USDA 5-8 · RHS H5 (13-24°C)

Watch for — Winter-wet corm rot: This species is notably prone to rotting in cold, sodden soil. Plant in gritty, free-draining woodland soil and avoid winter waterlogging, or lift and store the corm dry.

What cobra lily's hardiness rating actually means

Yes — cobra lily is genuinely cold hardy. Rated RHS H5 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. Its RHS rating of H5 means: Hardy in most of the UK and in cold winters. On the US scale that maps to USDA 5-8 — 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 −15 to −10 °C. Cobra Lily is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for cobra lily as it gets too cold:

It tolerates winter lows to about −15 to −10 °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 cobra lily go outside or overwinter — and where?

Plant it out within USDA 5-8 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 cobra lily can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Cobra Lily hardiness — frequently asked questions

Is cobra lily cold hardy?

Yes — cobra lily is genuinely cold hardy. Rated RHS H5 and USDA 5-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Cobra Lily is hardy across USDA 5-8; 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 cobra lily can survive?

Minimum survivable temperature is roughly about −15 to −10 °C. Cobra Lily is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is cobra lily?

Cobra Lily is rated USDA 5-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can cobra lily survive winter outside?

Plant it out within USDA 5-8 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 cobra lily below its minimum temperature?

It tolerates winter lows to about −15 to −10 °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.