Cold hardiness & minimum temperature

Is Squinancywort (Asperula cynanchica)cold hardy? Hardiness zone & min temp

Also called Squinancywort, Squinancy Wort.

More about squinancywort

About Squinancywort

Asperula cynanchica · also called Squinancywort, Squinancy Wort · flowering

Asperula cynanchica is a slender, low-growing perennial wildflower native to calcareous grasslands, chalk downland, and limestone pavement across Europe, including southern and central England. It produces a mass of tiny four-petalled pale pink flowers through summer, thriving in free-draining, alkaline, nutrient-poor soil in full sun. The single most important care requirement is excellent drainage on chalky or limestone-rich substrate — it will not tolerate rich or acidic soils. Toxicity to pets is not documented in the ASPCA database; as status is unconfirmed, treat as mildly-toxic.

Cold limit: USDA 4-8 · RHS H6 (-20 to 25°C)

What squinancywort's hardiness rating actually means

Yes — squinancywort is genuinely cold hardy. Rated RHS H6 and USDA 4-8, 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 4-8 — 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. Squinancywort is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for squinancywort 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 squinancywort go outside or overwinter — and where?

Plant it out within USDA 4-8 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 squinancywort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H6 figure above.

Squinancywort hardiness — frequently asked questions

Is squinancywort cold hardy?

Yes — squinancywort is genuinely cold hardy. Rated RHS H6 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Squinancywort is hardy across USDA 4-8; 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 squinancywort can survive?

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

What hardiness zone is squinancywort?

Squinancywort is rated USDA 4-8 and RHS H6 — Hardy throughout the UK and northern Europe.

Can squinancywort survive winter outside?

Plant it out within USDA 4-8 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 squinancywort 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.