Cold hardiness & minimum temperature

Is Blue Chalksticks (Curio repens (syn. Senecio serpens))cold hardy? Hardiness zone & min temp

Also called Blue chalksticks, Blue chalk sticks, Dwarf blue chalksticks, Blue finger, Dead man's fingers.

More about blue chalksticks

About Blue Chalksticks

Curio repens (syn. Senecio serpens) · also called Blue chalksticks, Blue chalk sticks · houseplant

Blue chalksticks (Curio repens, formerly Senecio serpens) is a low, spreading South African succulent grown for its powdery, chalky blue, finger-shaped leaves. Give it strong light, a gritty fast-draining mix, and infrequent soak-and-dry watering. Treat it as mildly toxic to pets; the ASPCA flags its close relative, string of pearls.

Cold limit: USDA USDA zones 9-11 (frost-tender; tolerates brief dips to roughly -7 C / 20 F but is damaged by hard frost). Grow as an indoor or container plant outside zones 9-11 and protect from freezing. (15-29 C)

What blue chalksticks's hardiness rating actually means

Blue Chalksticks is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Its RHS rating of H2 means: Tender — survives a frost-free greenhouse or a very mild, sheltered spot. On the US scale that maps to USDA USDA zones 9-11 (frost-tender; tolerates brief dips to roughly -7 C / 20 F but is damaged by hard frost). Grow as an indoor or container plant outside zones 9-11 and protect from freezing. — 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 1 to 5 °C — tolerates cold but no real frost. Blue Chalksticks shrugs off cold nights but a real, sustained freeze will kill it.

Concretely, for blue chalksticks as it gets too cold:

Down to roughly about 1 to 5 °C it copes, especially if dry and sheltered.
A sustained hard frost collapses the top growth; whether it returns depends on whether the roots, crown or tubers froze.
Wet cold is far more lethal than dry cold for this plant — soggy, frozen soil is the usual killer.

Can blue chalksticks go outside or overwinter — and where?

It can live outside year-round only in the mildest, most sheltered part of USDA USDA zones 9-11 (frost-tender; tolerates brief dips to roughly -7 C / 20 F but is damaged by hard frost). Grow as an indoor or container plant outside zones 9-11 and protect from freezing. or a frost-free UK microclimate.
In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter.
A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

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 blue chalksticks can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H2 figure above.

Frost protection for borderline blue chalksticks

Blue Chalksticks is right on a hardiness edge in many gardens, so if you are pushing it, these measures buy it the margin it needs:

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost.
Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse.
Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones.
Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.

Blue Chalksticks hardiness — frequently asked questions

Is blue chalksticks cold hardy?

Blue Chalksticks is half-hardy (RHS H2). It survives a mild winter outdoors in a sheltered spot, but a hard frost kills it — so in colder zones it is lifted, potted, or grown as a tender plant. Borderline outdoors. In its mild end of USDA USDA zones 9-11 (frost-tender; tolerates brief dips to roughly -7 C / 20 F but is damaged by hard frost). Grow as an indoor or container plant outside zones 9-11 and protect from freezing. (and sheltered UK gardens) blue chalksticks can stay out; in colder areas it must be lifted, brought in, or treated as a frost-tender plant.

What is the minimum temperature blue chalksticks can survive?

Minimum survivable temperature is roughly about 1 to 5 °C — tolerates cold but no real frost. Blue Chalksticks shrugs off cold nights but a real, sustained freeze will kill it.

What hardiness zone is blue chalksticks?

Blue Chalksticks is rated USDA USDA zones 9-11 (frost-tender; tolerates brief dips to roughly -7 C / 20 F but is damaged by hard frost). Grow as an indoor or container plant outside zones 9-11 and protect from freezing. and RHS H2 — Tender — survives a frost-free greenhouse or a very mild, sheltered spot.

Can blue chalksticks survive winter outside?

It can live outside year-round only in the mildest, most sheltered part of USDA USDA zones 9-11 (frost-tender; tolerates brief dips to roughly -7 C / 20 F but is damaged by hard frost). Grow as an indoor or container plant outside zones 9-11 and protect from freezing. or a frost-free UK microclimate. In colder zones, grow it in a pot you can move under cover, or lift its tubers/roots and store them frost-free over winter. A south-facing wall, free-draining soil and a dry winter position can push it a full zone hardier than the books suggest.

How do I protect blue chalksticks from frost?

Mulch the crown or root zone deeply with bark, straw or leaf-mould before the first hard frost. Move container plants against a warm wall or into an unheated but frost-free porch or greenhouse. Fleece the top growth on the coldest nights, and keep it on the dry side — dry roots survive cold far better than wet ones. Lift dahlia-type tubers or tender crowns after the first light frost blackens the foliage and store them somewhere cool but frost-free.