Cold hardiness & minimum temperature

Is Concrete Leaf (Titanopsis calcarea)cold hardy? Hardiness zone & min temp

Also called Concrete Leaf, Concrete Leaf Plant, Jewel Plant, Jewel Weed, Limestone Mimicry.

More about concrete leaf

Hardiness at a glance

USDA zone: USDA 9b-11 outdoors (some sources cite 8b with bone-dry winter protection); RHS hardiness H1C, so in the UK it is tender and best grown under glass, moved outside only in warm summer months.
RHS rating: H1b (derived)
Minimum survivable temperature: about 10 °C (sustained cold below this is damaging)
Comfortable growing range: 18-27C in growth; 10-16C during dormancy (65-80F in growth; 50-60F during dormancy)
Verdict: Indoor-only in almost every home. Concrete Leaf can only live outside year-round in genuinely frost-free climates (roughly USDA USDA 9b-11 outdoors (some sources cite 8b with bone-dry winter protection); RHS hardiness H1C, so in the UK it is tender and best grown under glass, moved outside only in warm summer months.); everywhere else it is a houseplant that summers out at most.

About Concrete Leaf

Titanopsis calcarea · also called Concrete Leaf, Concrete Leaf Plant · houseplant

Concrete Leaf (Titanopsis calcarea) is a tiny South African mesemb succulent whose warty, blue-grey rosettes mimic the limestone rubble it grows among. Give it bright direct sun, sharply draining gritty soil, and very sparing water — wet winters rot it. It is not ASPCA-listed; treat as mildly toxic and check with a vet.

Cold limit: USDA USDA 9b-11 outdoors (some sources cite 8b with bone-dry winter protection); RHS hardiness H1C, so in the UK it is tender and best grown under glass, moved outside only in warm summer months. (18-27C in growth; 10-16C during dormancy)

Watch for — Root rot from overwatering: The most common killer. Soggy soil, poor drainage or watering during summer/winter dormancy rots the roots. Use a gritty mix, water only when bone dry, and keep it dry in cold or hot spells.

What concrete leaf's hardiness rating actually means

Concrete Leaf is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Its RHS rating of H1b means: Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season. On the US scale that maps to USDA USDA 9b-11 outdoors (some sources cite 8b with bone-dry winter protection); RHS hardiness H1C, so in the UK it is tender and best grown under glass, moved outside only in warm summer months. — 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 10 °C (sustained cold below this is damaging). Concrete Leaf has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for concrete leaf as it gets too cold:

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches.
A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover.
Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.

Can concrete leaf go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually.
Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C.
It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

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 concrete leaf can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1b figure above.

Concrete Leaf hardiness — frequently asked questions

Is concrete leaf cold hardy?

Concrete Leaf is not cold hardy. It is a tropical houseplant that dies if it is left out through frost — there is no zone where it overwinters outdoors in a UK or cold-US climate. Indoor-only in almost every home. Concrete Leaf can only live outside year-round in genuinely frost-free climates (roughly USDA USDA 9b-11 outdoors (some sources cite 8b with bone-dry winter protection); RHS hardiness H1C, so in the UK it is tender and best grown under glass, moved outside only in warm summer months.); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature concrete leaf can survive?

What hardiness zone is concrete leaf?

Concrete Leaf is rated USDA USDA 9b-11 outdoors (some sources cite 8b with bone-dry winter protection); RHS hardiness H1C, so in the UK it is tender and best grown under glass, moved outside only in warm summer months. and RHS H1b — Sub-tropical — a normal warm home is fine, but it cannot go outside in a cool season.

Can concrete leaf survive winter outside?

It can holiday outdoors in summer once nights are reliably above 10 °C, in shade or dappled light, hardened off gradually. Bring it back indoors well before the first autumn frost — do not wait for a frost warning, move it when nights drop toward 10-12 °C. It will never overwinter outside in a temperate climate; the indoors is its winter home, full stop.

What happens to concrete leaf below its minimum temperature?

Below about about 10 °C, growth stalls and the leaves start to show cold stress — dark, water-soaked, or yellowing patches. A single light frost blackens the foliage; a hard freeze kills the whole plant, roots included, and it does not recover. Even a cold, draughty windowsill or an unheated porch in winter can be enough to damage it permanently.