Cold hardiness & minimum temperature

Is Four-angled cassiope (Cassiope tetragona)cold hardy? Hardiness zone & min temp

Also called Four-angled cassiope, Arctic white heather.

More about four-angled cassiope

About Four-angled cassiope

Cassiope tetragona · also called Four-angled cassiope, Arctic white heather · flowering

Four-angled cassiope is a compact arctic-alpine subshrub bearing tightly scale-like leaves arranged in four ranks along its stems, giving them a distinctive square cross-section. Solitary white bell-shaped flowers dangle from wiry red stalks in late spring. It thrives in cool, moist, acidic conditions and is suited to rock gardens in cold climates.

Cold limit: USDA 2-6 · RHS H7 (−30 to 15°C)

Watch for — Failure to flower: Often caused by insufficient winter cold or inadequate cool dormancy. This species needs genuine cold winters (below freezing) to initiate flowering. In mild climates, bloom may be sparse or absent.

What four-angled cassiope's hardiness rating actually means

Yes — four-angled cassiope is genuinely cold hardy. Rated RHS H7 and USDA 2-6, 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 2-6 — 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. Four-angled cassiope is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for four-angled cassiope 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 four-angled cassiope go outside or overwinter — and where?

Plant it out within USDA 2-6 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 four-angled cassiope can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Four-angled cassiope hardiness — frequently asked questions

Is four-angled cassiope cold hardy?

Yes — four-angled cassiope is genuinely cold hardy. Rated RHS H7 and USDA 2-6, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Four-angled cassiope is hardy across USDA 2-6; 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 four-angled cassiope can survive?

Minimum survivable temperature is roughly below about −20 °C. Four-angled cassiope is built for winter — once established it takes hard frost and snow in its stride.

What hardiness zone is four-angled cassiope?

Four-angled cassiope is rated USDA 2-6 and RHS H7 — Hardy in the severest European continental winters.

Can four-angled cassiope survive winter outside?

Plant it out within USDA 2-6 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 four-angled cassiope 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.