Cold hardiness & minimum temperature

Is Cobweb Spiderwort (Cyanotis arachnoidea)cold hardy? Hardiness zone & min temp

Also called Cobweb Spiderwort, White Grass of the Dew, Grass of the Dew.

More about cobweb spiderwort

About Cobweb Spiderwort

Cyanotis arachnoidea · also called Cobweb Spiderwort, White Grass of the Dew · houseplant

Cyanotis arachnoidea is a creeping, softly hairy perennial from tropical Africa and Asia, bearing cobalt-blue or pink three-petalled flowers. Its prostrate stems root freely at nodes, making it an excellent groundcover or trailing basket plant. It needs bright light, well-draining soil, and warm, humid conditions.

Cold limit: USDA 10-12 · RHS H1c (18–30°C (min 10°C))

What cobweb spiderwort's hardiness rating actually means

Cobweb Spiderwort 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 H1c means: Warm-temperate — can summer outdoors but must come in well before the first frost. On the US scale that maps to USDA 10-12 — 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 5 °C (and never frost). Cobweb Spiderwort has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for cobweb spiderwort as it gets too cold:

Below about about 5 °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 cobweb spiderwort go outside or overwinter — and where?

It can holiday outdoors in summer once nights are reliably above 5 °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 cobweb spiderwort can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Cobweb Spiderwort hardiness — frequently asked questions

Is cobweb spiderwort cold hardy?

Cobweb Spiderwort 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. Cobweb Spiderwort can only live outside year-round in genuinely frost-free climates (roughly USDA 10-12); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature cobweb spiderwort can survive?

Minimum survivable temperature is roughly about 5 °C (and never frost). Cobweb Spiderwort has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

What hardiness zone is cobweb spiderwort?

Cobweb Spiderwort is rated USDA 10-12 and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can cobweb spiderwort survive winter outside?

It can holiday outdoors in summer once nights are reliably above 5 °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 cobweb spiderwort below its minimum temperature?

Below about about 5 °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.