Cold hardiness & minimum temperature

Is Split Rock (Pleiospilos nelii)cold hardy? Hardiness zone & min temp

Also called split rock, splitrock, living granite, mimicry plant, cleft stone.

More about split rock

About Split Rock

Pleiospilos nelii · also called split rock, splitrock · houseplant

Split Rock is a stone-mimicking succulent (a mesemb from South Africa's Karoo) that looks like a cleft pebble. It grows one new leaf pair a year that absorbs the old one, needs intense light and almost no water in summer and winter, and rots easily if overwatered. Pet-safe by ASPCA standards.

Cold limit: USDA 9b-11b (bring indoors below about -1°C / 30°F) (18-29°C (active growth); cool winter rest near 5-13°C)

Watch for — Refuses to flower: Usually a missing dormancy — give a cool, nearly dry winter rest with strong light to trigger the daisy-like autumn-to-spring blooms.

What split rock's hardiness rating actually means

Yes — split rock is genuinely cold hardy. Rated RHS H7 and USDA 9b-11b (bring indoors below about -1°C / 30°F), 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 9b-11b (bring indoors below about -1°C / 30°F) — 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. Split Rock is built for winter — once established it takes hard frost and snow in its stride.

Concretely, for split rock 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 split rock go outside or overwinter — and where?

Plant it out within USDA 9b-11b (bring indoors below about -1°C / 30°F) 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 split rock can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H7 figure above.

Split Rock hardiness — frequently asked questions

Is split rock cold hardy?

Yes — split rock is genuinely cold hardy. Rated RHS H7 and USDA 9b-11b (bring indoors below about -1°C / 30°F), it lives outdoors all year and needs winter cold rather than protection from it. An outdoor plant. Split Rock is hardy across USDA 9b-11b (bring indoors below about -1°C / 30°F); 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 split rock can survive?

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

What hardiness zone is split rock?

Split Rock is rated USDA 9b-11b (bring indoors below about -1°C / 30°F) and RHS H7 — Hardy in the severest European continental winters.

Can split rock survive winter outside?

Plant it out within USDA 9b-11b (bring indoors below about -1°C / 30°F) 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 split rock 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.