Romaine Lettuce

Lactuca sativa var. longifolia

Also called cos lettuce

EasyGrows in pots

Romaine lettuce, also called cos, is a cool-season leafy green grown from seed in spring or fall. It forms upright heads, grows in full sun to partial shade, and needs steady moisture.

Quick facts

Germination time: 7–10 days
Germination temperature: 16–27 °C61–81 °F
Sowing depth: 6 mm–1.5 cm¼–½ in
Spacing between plants: 20–30 cm8–12 in
Days to maturity: Not yet verified
Sun: Full sun, partial shade

Safety for cats and dogs: not yet verified.

Compare with another seed How to grow it

By SeedBattle EditorsUpdated Oct 19, 2026

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01 · Overview

About romaine lettuce

Romaine or cos is a cool-season lettuce that forms upright heads with wavy, attractive leaves. It is relatively easy to grow, and it does better in heat than head lettuce.

The leaves can be eaten raw or cooked in salads, sandwiches and other dishes.

Growing details

Start indoors: Not yet verified
Sow outdoors: 2–3 weeks before the last frost
Water: Moderate
Containers: Yes, 1.9 L or largerYes, 2 qt or larger
Height: 15–30 cm6–12 in
Spread: 15–30 cm6–12 in
Frost tolerance: Half-hardy (light frost)
Soil pH: pH 6.0–6.5
Life cycle: Not yet verified

Sowing timeline

When to sow romaine lettuce seeds

Counted from your area's average last spring frost date. Find yours from a local weather service or garden center, then count back or forward.

Sow outdoors2–3 weeks before the last frost

Germination time: 7–10 days
Germination temperature: 16–27 °C61–81 °F
Frost tolerance: Half-hardy (light frost)

02 · How to grow

How to grow romaine lettuce from seed

Sowing. Sow seeds outdoors about 2 to 3 weeks before the last frost. You can also start seeds indoors 6 to 8 weeks before the last frost and transplant them later. For a fall crop, sow about three months before the first frost.

Depth and germination. Plant seeds ¼ inch (0.6 cm) to ½ inch (1.3 cm) deep. Seeds emerge in 7 to 10 days, and the optimum soil temperature for germination is 60 to 80 °F (16 to 27 °C).

Spacing and sun. Thin plants to 8 to 12 inches (20 to 30 cm) apart in the row. Give plants full sun to partial shade. Sow more seed every two weeks to extend the harvest.

Containers. Romaine can be grown in a container at least 2 quarts (1.9 L) in volume and 6 to 8 inches (15 to 20 cm) deep.

03 · Care

Caring for romaine lettuce

Watering. Lettuce has a shallow root system and needs consistently moist soil. Water often enough to keep a uniform moisture supply, especially while seedlings are getting established. Mulch helps conserve soil moisture and limits weeds.

Tipburn. Drought and uneven soil moisture are the most significant causes of tipburn, a calcium-related disorder that browns leaf edges.

Weeds. Lettuce seedlings compete poorly with weeds, so cultivate shallowly to avoid root injury.

At a glance

How romaine lettuce compares with other vegetables

Worked out from the growing facts of the 79 seeds in Vegetables on SeedBattle.

Romaine Lettuce
Each of the other vegetables
Their average

See all vegetables

Germination timeSprouts sooner than average
7–10 days
Average for vegetables: 10 days, from 39 other seeds
Germination temperatureCooler than average
16–27 °C61–81 °F
Average for vegetables: 23 °C73 °F, from 38 other seeds
Sowing depthShallower than average
6 mm–1.5 cm¼–½ in
Average for vegetables: 1 cm½ in, from 58 other seeds
Spacing between plantsCloser than average
20–30 cm8–12 in
Average for vegetables: 35 cm14 in, from 43 other seeds
HeightShorter than average
15–30 cm6–12 in
Average for vegetables: 94 cm3 ft, from 57 other seeds

04 · Problems

Common romaine lettuce problems

Bolting. High temperatures of 70 to 80 °F (21 to 27 °C) or dry soil can make plants flower, turning the leaves bitter and stopping leaf production.

Pests. Aphids, armyworms, imported cabbage worms and loopers attack lettuce. Slugs and snails may feed on the foliage.

Diseases. Damping-off is a serious disease of young seedlings, while mildews and sclerotinia are serious on mature plants.

05 · Harvest

Harvesting romaine lettuce

Pick the outer leaves first so the central leaves can keep growing. Baby leaves about 2 to 3 inches (5 to 8 cm) long can be picked for a continuous harvest. Romaine is ready when the leaves have elongated and overlap to form a partly tight head about 6 to 8 inches (15 to 20 cm) tall.

06 · Storage

Storing romaine lettuce

Lettuce generally keeps 2 to 3 weeks in very cool (32 °F or 0 °C), moist conditions with about 95% humidity.

07 · Safety

Romaine Lettuce safety

Handling the sap of lettuce plants can cause contact dermatitis, a skin irritation; the source rates the severity as low.

Romaine Lettuce questions

When should I plant romaine lettuce?

For a spring crop, you can sow seeds outdoors about 2 to 3 weeks before the last frost, or start them indoors 6 to 8 weeks before the last frost for later transplanting. For a fall crop, sow about three months before the first frost.

How long do romaine lettuce seeds take to germinate?

Lettuce seeds emerge in about 7 to 10 days and germinate best at 55 to 65 °F (13 to 18 °C). The optimum soil temperature for germination is 60 to 80 °F (16 to 27 °C).