Cold hardiness & minimum temperature

Is Autumn Squill (Scilla autumnalis)cold hardy? Hardiness zone & min temp

Also called Autumn Squill, Fall Squill.

More about autumn squill

About Autumn Squill

Scilla autumnalis · also called Autumn Squill, Fall Squill · flowering

Autumn Squill is a delicate, leafless-when-flowering bulb native to Mediterranean Europe, producing slender spikes of pale lilac-pink to violet-blue stars from late summer into autumn. Perfect for rocky, sunny slopes and dry meadow gardens. All Scilla species are toxic to dogs, cats, and horses; keep away from pets.

Cold limit: USDA 5-9 · RHS H5 (5-25°C)

What autumn squill's hardiness rating actually means

Yes — autumn squill is genuinely cold hardy. Rated RHS H5 and USDA 5-9, 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 5-9 — 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 −15 to −10 °C. Autumn Squill is built for winter — once established it takes hard frost and snow in its stride.

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

Plant it out within USDA 5-9 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 autumn squill can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Autumn Squill hardiness — frequently asked questions

Is autumn squill cold hardy?

Yes — autumn squill is genuinely cold hardy. Rated RHS H5 and USDA 5-9, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Autumn Squill is hardy across USDA 5-9; 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 autumn squill can survive?

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

What hardiness zone is autumn squill?

Autumn Squill is rated USDA 5-9 and RHS H5 — Hardy in most of the UK and in cold winters.

Can autumn squill survive winter outside?

Plant it out within USDA 5-9 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 autumn squill 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.