Cold hardiness & minimum temperature

Is Aster 'October Skies' (Symphyotrichum oblongifolium 'October Skies')cold hardy? Hardiness zone & min temp

Also called Aromatic Aster, Fall Aster, Oblongleaf Aster.

More about aster 'october skies'

About Aster 'October Skies'

Symphyotrichum oblongifolium 'October Skies' · also called Aromatic Aster, Fall Aster · flowering

A compact, mounded native aster bearing masses of lavender-blue daisy flowers from late September into November. Exceptionally drought-tolerant once established and notably resistant to powdery mildew. Valued by pollinators and birds. Not listed as toxic by the ASPCA for dogs or cats.

Cold limit: USDA 3-9 · RHS H7 (−35 to 35°C)

What aster 'october skies''s hardiness rating actually means

Yes — aster 'october skies' 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. Aster 'October Skies' is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for aster 'october skies' 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 aster 'october skies' 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 aster 'october skies' can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Aster 'October Skies' hardiness — frequently asked questions

Is aster 'october skies' cold hardy?

Yes — aster 'october skies' 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. Aster 'October Skies' 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 aster 'october skies' can survive?

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

What hardiness zone is aster 'october skies'?

Aster 'October Skies' is rated USDA 3-9 and RHS H7 — Hardy in the severest European continental winters.

Can aster 'october skies' 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 aster 'october skies' 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.