What hardiness zones is Lactuca sativa 'Romaine' suitable for?

Lactuca sativa 'Romaine' is suitable for USDA hardiness zones 2, 3, 4, 5, 6, 7, 8, 9.

What are the sun requirements for Lactuca sativa 'Romaine'?

Lactuca sativa 'Romaine' requires Part Sun.

How much water does Lactuca sativa 'Romaine' need?

Lactuca sativa 'Romaine' has Medium water needs.

Vegetables

Lactuca sativa 'Romaine'

Romaine Lettuce

Asteraceae

Cultivar group of garden origin (species derived from Lactuca serriola, native to Mediterranean/Middle East)

At a Glance

TypeAnnual

HabitUpright

FoliageDeciduous

Height10-16 inches (25-40 cm)

Width8-12 inches (20-30 cm)

Growing Zones

USDA Hardiness Zones

2 - 9

Zone 2

Zone 3

Zone 4

Zone 5

Zone 6

Zone 7

Zone 8

Zone 9

These zones indicate the coldest temperatures this plant can typically survive.

Frost Tolerancehardy

Key Features

Container Friendly

Maintenancelow

Overview

Lactuca sativa 'Romaine' is an upright, elongated-head annual in the daisy family (Asteraceae) reaching 10–16 inches (25–40 cm) tall with an 8–12 inch (20–30 cm) spread. This cultivar type produces a tall, cylindrical, loosely folded head of elongated leaves rather than the rounded heads of iceberg or the loose rosettes of leaf lettuce. Outer leaves are dark green, 8–12 inches (20–25 cm) long, with thick, crunchy, white midribs that provide the characteristic crisp texture. Inner leaves are pale yellow-green, more tightly folded. Milky latex (containing lactucarium, a mild sedative compound) exudes from cut stems — a trait shared with all Lactuca. The upright, elongated head shape and prominent crunchy midrib distinguish romaine from all other lettuce types. Bolts in response to heat above 80°F (27°C) and long day lengths above 14 hours. In the Pacific Northwest, the cool maritime climate extends the growing season compared to warmer inland regions. Open-pollinated romaine types are used in seed-saving education — Lactuca sativa is primarily self-pollinating with minimal isolation requirements.

Native Range

Lactuca sativa was domesticated from L. serriola (prickly lettuce) in the Middle East approximately 4,500 years ago. Romaine (cos) lettuce originated in the eastern Mediterranean, likely Egypt or Greece. The name 'cos' refers to the Greek island of Kos.

Suggested Uses

Planted in vegetable gardens, salad gardens, raised beds, and containers (3+ gallon). The standard lettuce for Caesar salad and grilled lettuce preparations. The thick midribs hold dressings and provide crunch. Container-grown on balconies and patios. The self-pollinating habit and open-pollinated seed availability make romaine a primary seed-saving teaching lettuce — easier than cross-pollinating crops like beet or brassicas.

How to Identify

Distinguished from iceberg (crisphead) lettuce by the tall, elongated, open head (versus round, tightly wrapped). Distinguished from leaf lettuce by the upright growth habit and thick, crunchy white midribs (versus thinner, flexible leaves). Distinguished from butterhead by the crisp (versus soft, buttery) texture. The milky latex when stems are cut confirms Lactuca. The upright cylindrical head with prominent white midribs is diagnostic for romaine.

Appearance

Size & Dimensions

Height10" - 1'4"

Width/Spread8" - 1'

Colors

Flower Colors

yellow

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~2 weeks

Summer

Bolts in response to heat above 80°F (27°C) and day lengths above 14 hours. The seed stalk elongates rapidly from the center of the head, reaching 36–48 inches (90–120 cm). Flowers are small, yellow, all-ligulate (typical Asteraceae-Cichorieae). Primarily self-pollinating; isolation of 10–25 feet (3–8 m) is sufficient for seed purity. Seeds mature 2–3 weeks after flowering.

Detailed Descriptions

Flower Description

Yellow (if allowed to bolt)

Foliage Description

Medium to dark green, elongated, upright, with a thick, crunchy white midrib; outer leaves darker, inner leaves pale yellow-green

Growing Conditions

Sun Requirements

Full Sun

Partial Shade

Requires 3-8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 7.0(Neutral)

357912

Soil Types

loamsilt

Drainage

moist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Care & Maintenance

Care Guide

Start seeds indoors 4 weeks before the last frost or direct sow 3–4 weeks before the last frost, 0.25 inch (6 mm) deep. Space 10 inches (25 cm) apart. Successive sowings every 2 weeks extend harvest. In the Pacific Northwest, sow from March through May for spring/summer harvest, and August–September for fall harvest. Consistent moisture prevents bitterness and premature bolting. Partial shade in warm weather extends the harvest. Harvest full heads at 60–75 days by cutting at the base, or harvest outer leaves progressively for cut-and-come-again use. The thick midribs are the primary texture component — harvest before bolting for the crispest, mildest leaves.

Pruning

Harvest outer leaves at the base for cut-and-come-again use, or harvest the entire head by cutting at the soil line. Remove bolting stems promptly — once bolting begins, leaves become bitter due to increased lactucarium concentration.

Maintenance Level

low

Container Growing

✓ Suitable for container growing

Minimum container size: 3 gallons

⚠️ Toxicity Warning

Non-toxic

Planting Guide

Planting Methods & Timing

Planting Method

both

Indoor Start

4 weeks before last frost

Direct Sow Timing

3-4 weeks before last frost; successive sowings every 2 weeks through spring; resume in late summer

Days to Maturity

60–75 days

Plant Spacing

10 inches

Companion Planting

Good Companions

carrot

radish

strawberry

chive

Avoid Planting With

celery

parsley