Cold hardiness & minimum temperature

Is Holy Basil (Tulsi) (Ocimum tenuiflorum)cold hardy? Hardiness zone & min temp

Also called Tulsi, Sacred Basil.

More about holy basil (tulsi)

About Holy Basil (Tulsi)

Ocimum tenuiflorum · also called Tulsi, Sacred Basil · herb

Holy basil, or tulsi, is a tender aromatic herb in the mint family grown for its clove-scented leaves used in cooking and Ayurvedic tea. It loves heat and full sun, grows fast as a soft-stemmed annual in most climates, and rewards frequent pinching. Treat it as a warm-season annual unless grown indoors over winter.

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

Watch for — Cold damage: Leaves blacken below about 10°C. Bring indoors or protect when nights turn cool; it has no frost tolerance.

What holy basil (tulsi)'s hardiness rating actually means

Holy Basil (Tulsi) 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). Holy Basil (Tulsi) has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Holy Basil (Tulsi) hardiness — frequently asked questions

Is holy basil (tulsi) cold hardy?

Holy Basil (Tulsi) 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. Holy Basil (Tulsi) 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 holy basil (tulsi) can survive?

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

What hardiness zone is holy basil (tulsi)?

Holy Basil (Tulsi) 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 holy basil (tulsi) 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 holy basil (tulsi) 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.