Cold hardiness & minimum temperature

Is Red Romaine Lettuce (Lactuca sativa var. longifolia 'Rouge d'Hiver')cold hardy? Hardiness zone & min temp

Also called Rouge d'Hiver lettuce, red winter lettuce, red romaine.

More about red romaine lettuce

About Red Romaine Lettuce

Lactuca sativa var. longifolia 'Rouge d'Hiver' · also called Rouge d'Hiver lettuce, red winter lettuce · edible

'Rouge d'Hiver' is a French heirloom red romaine with upright, bronze-red tinged leaves and crisp green hearts. It is unusually cold-hardy for a romaine, making it a reliable autumn, overwintered and early-spring crop. Cool weather and bright light deepen the red colouring; heat and long days fade the colour and push it to bolt and turn bitter.

Cold limit: USDA 4-9 (cool-season annual; overwinters in mild zones) · RHS H3 (10-20°C)

Watch for — Bolting in heat: Hot weather and long days send romaine to seed, turning leaves milky and bitter. Grow it in spring, autumn or overwintered, and choose shadier spots in summer.

What red romaine lettuce's hardiness rating actually means

Hardiness works differently for red romaine lettuce: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". Its RHS rating of H3 means: Half-hardy — comes through mild UK winters outside but is killed by a hard freeze. On the US scale that maps to USDA 4-9 (cool-season annual; overwinters in mild zones) — 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

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

Concretely, for red romaine lettuce as it gets too cold:

Light frost (around 0 to −2 °C) damages or kills tender summer crops outright; cold-hardy types take a few degrees of frost.
The plant does not "survive winter" — its life cycle simply ends, by design, when frost arrives or it finishes cropping.
A surprise late spring frost can also kill young transplants set out too early, before the season even starts.

Can red romaine lettuce go outside or overwinter — and where?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost.
In short-season zones, start it indoors or under cover to stretch the effective growing window.
Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

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 red romaine lettuce can be outside. US growers can check USDA zones; UK growers should use the RHS hardiness ratings, which match the H3 figure above.

Frost protection for borderline red romaine lettuce

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

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks.
Have row cover ready for an unexpected late spring or early autumn frost.
Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.

Red Romaine Lettuce hardiness — frequently asked questions

Is red romaine lettuce cold hardy?

Hardiness works differently for red romaine lettuce: it is grown as a seasonal crop, not overwintered. The question is not "what zone" but "how long is your frost-free growing window". A seasonal crop, not a perennial. Red Romaine Lettuce is grown 4-9 (cool-season annual; overwinters in mild zones); you sow after the last frost and harvest before the first one, then start again next year.

What is the minimum temperature red romaine lettuce can survive?

As an annual crop, its "minimum temperature" is the first hard frost — that is the end of the plant's life, not a survivable low. Many types are also damaged by light frost (around 0 °C).

What hardiness zone is red romaine lettuce?

Red Romaine Lettuce is rated USDA 4-9 (cool-season annual; overwinters in mild zones) and RHS H3 — Half-hardy — comes through mild UK winters outside but is killed by a hard freeze.

Can red romaine lettuce survive winter outside?

Time it to your frost dates: sow or plant out after the last spring frost, and aim to harvest before the first autumn frost. In short-season zones, start it indoors or under cover to stretch the effective growing window. Hardier crops in this group can be sown for an autumn or overwintered harvest in mild zones — check the specific crop.

How do I protect red romaine lettuce from frost?

Use fleece, cloches or a cold frame at each end of the season to dodge a borderline frost and add growing weeks. Have row cover ready for an unexpected late spring or early autumn frost. Know your local last- and first-frost dates and count back the crop’s days-to-maturity to schedule the sowing.