Cold hardiness & minimum temperature

Is Bitterroot Lewisia (Lewisia cotyledon)cold hardy? Hardiness zone & min temp

Also called Bitterroot Lewisia, Siskiyou Lewisia, Cliff Maids.

More about bitterroot lewisia

About Bitterroot Lewisia

Lewisia cotyledon · also called Bitterroot Lewisia, Siskiyou Lewisia · flowering

A stunning alpine perennial from the Siskiyou mountains of northern California and southern Oregon, producing vivid pink, orange, or bicoloured flowers on stiff stems above rosettes of strap-like, evergreen leaves. Outstanding in walls, alpine troughs, and vertical rockwork; demands perfect drainage and summer dryness to thrive.

Cold limit: USDA 5–8 · RHS H5 (-10 to 25°C)

Watch for — Botrytis (grey mould): Fungal grey mould develops in cold, wet, still conditions. Improve ventilation, remove dead foliage, and use a systemic fungicide if needed. An alpine house or cold frame in wet winters is effective prevention.

What bitterroot lewisia's hardiness rating actually means

Yes — bitterroot lewisia is genuinely cold hardy. Rated RHS H5 and USDA 5–8, 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 5–8 — 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 −15 to −10 °C. Bitterroot Lewisia is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for bitterroot lewisia 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 bitterroot lewisia go outside or overwinter — and where?

Plant it out within USDA 5–8 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 bitterroot lewisia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Bitterroot Lewisia hardiness — frequently asked questions

Is bitterroot lewisia cold hardy?

Yes — bitterroot lewisia is genuinely cold hardy. Rated RHS H5 and USDA 5–8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Bitterroot Lewisia is hardy across USDA 5–8; 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 bitterroot lewisia can survive?

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

What hardiness zone is bitterroot lewisia?

Bitterroot Lewisia is rated USDA 5–8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can bitterroot lewisia survive winter outside?

Plant it out within USDA 5–8 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 bitterroot lewisia 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.