Cold hardiness & minimum temperature

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

Also called Siskiyou Lewisia, Cliff Maids, Broadleaf Lewisia.

More about siskiyou lewisia

About Siskiyou Lewisia

Lewisia cotyledon · also called Siskiyou Lewisia, Cliff Maids · flowering

Native to rocky cliffs and outcrops in the Siskiyou and Klamath mountains of northern California and southern Oregon, Lewisia cotyledon is an evergreen rosette perennial prized for its spectacular sprays of funnel-shaped flowers in shades from white and pale pink through to vivid orange, yellow, and magenta. It demands sharply drained, humus-rich, acidic to neutral gritty soil and resents winter wet around its crown above all else; planting on its side in a wall crevice or in a raised alpine trough dramatically improves survival. It holds the RHS Award of Garden Merit. Lewisia is not documented by the ASPCA as toxic; it is considered mildly-toxic as a precaution since definitive non-toxic listing is absent.

Cold limit: USDA 4-8 · RHS H5 (-15 to 25°C)

Watch for — Crown and neck rot: The most common cause of death; wet conditions at the crown — especially in winter — cause rapid fungal rot. Prevent by planting at an angle, using a grit collar, and ensuring overhead protection in wet climates.

What siskiyou lewisia's hardiness rating actually means

Yes — siskiyou lewisia is genuinely cold hardy. Rated RHS H5 and USDA 4-8, 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 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 −15 to −10 °C. Siskiyou Lewisia is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for siskiyou 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 siskiyou lewisia 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 siskiyou lewisia can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H5 figure above.

Siskiyou Lewisia hardiness — frequently asked questions

Is siskiyou lewisia cold hardy?

Yes — siskiyou lewisia is genuinely cold hardy. Rated RHS H5 and USDA 4-8, it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Siskiyou Lewisia 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 siskiyou lewisia can survive?

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

What hardiness zone is siskiyou lewisia?

Siskiyou Lewisia is rated USDA 4-8 and RHS H5 — Hardy in most of the UK and in cold winters.

Can siskiyou lewisia 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 siskiyou 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.