Cold hardiness & minimum temperature

Is Lettuce Leaf Basil (Ocimum basilicum 'Napoletano')cold hardy? Hardiness zone & min temp

Also called lettuce leaf basil, Neapolitan basil.

More about lettuce leaf basil

About Lettuce Leaf Basil

Ocimum basilicum 'Napoletano' · also called lettuce leaf basil, Neapolitan basil · herb

Lettuce leaf basil is a large-leaved Italian sweet basil whose huge, crinkled, lettuce-like leaves are ideal for wrapping and tearing into salads. A tender warm-season annual, it demands heat, full sun and rich, moist soil, grows vigorously, and is best kept productive by frequent harvesting and pinching out flowers before it bolts.

Cold limit: USDA 10-11 as a tender perennial; grown as a warm-season annual in most regions · RHS H1c (18-27°C)

Watch for — Frost and cold damage: Like all basil it is frost-tender and blackens below about 10°C. Plant out only after frost has passed and bring potted plants in before cold nights.

What lettuce leaf basil's hardiness rating actually means

Lettuce Leaf 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 as a tender perennial; grown as a warm-season annual in most regions — 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). Lettuce Leaf Basil has no frost tolerance at all — it is an indoor plant in any climate with a real winter.

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

Lettuce Leaf Basil hardiness — frequently asked questions

Is lettuce leaf basil cold hardy?

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

What is the minimum temperature lettuce leaf basil can survive?

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

What hardiness zone is lettuce leaf basil?

Lettuce Leaf Basil is rated USDA 10-11 as a tender perennial; grown as a warm-season annual in most regions and RHS H1c — Warm-temperate — can summer outdoors but must come in well before the first frost.

Can lettuce leaf 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 lettuce leaf 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.