Cold hardiness & minimum temperature

Is Purple Ruffles Basil (Ocimum basilicum 'Purple Ruffles')cold hardy? Hardiness zone & min temp

Also called Purple Basil.

More about purple ruffles basil

About Purple Ruffles Basil

Ocimum basilicum 'Purple Ruffles' · also called Purple Basil · herb

Purple Ruffles is an ornamental culinary basil prized for deep burgundy, frilled, fringed leaves that add colour to beds and plates. It is slightly slower and fussier than green basil, needing warmth and full sun to keep its dark pigment. Grown as a tender warm-season annual, it pairs looks with a clove-tinged sweet-basil flavour.

Cold limit: USDA 10-11 (grown as a warm-season annual elsewhere) · RHS H1c (18-30°C)

What purple ruffles basil's hardiness rating actually means

Purple Ruffles Basil 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 10-11 (grown as a warm-season annual elsewhere) — 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). Purple Ruffles Basil has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

Concretely, for purple ruffles basil 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 purple ruffles basil 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 purple ruffles basil can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H1c figure above.

Purple Ruffles Basil hardiness — frequently asked questions

Is purple ruffles basil cold hardy?

Purple Ruffles Basil 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. Purple Ruffles Basil can only live outside year-round in genuinely frost-free climates (roughly USDA 10-11 (grown as a warm-season annual elsewhere)); everywhere else it is a houseplant that summers out at most.

What is the minimum temperature purple ruffles basil can survive?

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

What hardiness zone is purple ruffles basil?

Purple Ruffles Basil is rated USDA 10-11 (grown as a warm-season annual elsewhere) and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can purple ruffles basil 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 purple ruffles basil 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.