Cold hardiness & minimum temperature

Is Alpine Squill (Scilla bifolia)cold hardy? Hardiness zone & min temp

Also called Alpine Squill, Two-leaved Squill.

More about alpine squill

About Alpine Squill

Scilla bifolia · also called Alpine Squill, Two-leaved Squill · flowering

Scilla bifolia is a dainty bulbous perennial native to woodland edges, alpine meadows, and rocky hillsides across central Europe, from the Alps to the Caucasus. It is one of the earliest spring bulbs to flower, producing loose racemes of starry, intense gentian-blue flowers (occasionally pink or white) in late winter to early spring before most other plants emerge. It naturalises readily under deciduous trees and in short grass. The RHS awarded it its Award of Garden Merit in 1993. All parts are toxic to cats and dogs due to cardiac glycoside compounds.

Cold limit: USDA 3-8 · RHS H6 (-20 to 18°C)

What alpine squill's hardiness rating actually means

Yes — alpine squill is genuinely cold hardy. Rated RHS H6 and USDA 3-8, 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 3-8 — 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 −20 to −15 °C. Alpine Squill is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for alpine squill 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 alpine squill go outside or overwinter — and where?

Plant it out within USDA 3-8 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 alpine squill can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Alpine Squill hardiness — frequently asked questions

Is alpine squill cold hardy?

Yes — alpine squill is genuinely cold hardy. Rated RHS H6 and USDA 3-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Alpine Squill is hardy across USDA 3-8; 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 alpine squill can survive?

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

What hardiness zone is alpine squill?

Alpine Squill is rated USDA 3-8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can alpine squill survive winter outside?

Plant it out within USDA 3-8 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 alpine squill 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.