How to Grow Cos Lettuce
Wikimedia Commons
Cos Lettuce
Lactuca sativa var. longifolia
vegetableCos lettuce, also known as Romaine lettuce, is a crisp, elongated leafy green with a firm heart and mild flavor. It features upright growth with elongated leaves that become progressively lighter toward the center. This versatile lettuce is widely used in salads, wraps, and Caesar salads.
Looking for a specific variety?
When should you plant Cos Lettuce in your zone?
Get a personalized planting timeline — when to start seeds, transplant, and harvest — based on your USDA zone and local frost dates. Free to start.
Example Cos Lettuce timeline · Pittsburgh, PA (Zone 6b)
-
Plant Cos Lettuce
Around Apr 17Near Pittsburgh's average last spring frost.
-
Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
-
Harvest Cos Lettuce
Around Jun 11≈ 55 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Cos Lettuce dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 4-9; can be grown year-round in mild climates
Sign up free to see if Cos Lettuce grows in your zone — and get a personalized planting timeline.
Get my Cos Lettuce timeline →Growth Stages
Seedling
2-3 weeksSmall cotyledons emerge with 2-4 true leaves visible; plant is delicate and tender
Keep soil moist, provide bright indirect light, thin seedlings to proper spacing to prevent crowding and damping off
Vegetative Growth
3-4 weeksUpright rosette of dark green leaves forms; plant establishes robust root system and increases leaf production
Maintain consistent moisture, provide full sun, begin fertilizing with balanced fertilizer every 2-3 weeks, thin to proper spacing
Head Development
2-3 weeksInner leaves begin to blanch and lighten in color; heart of plant becomes more compact and dense with elongated texture
Continue watering consistently, avoid overhead watering to prevent head rot, monitor for pests, mulch around base to retain moisture
Maturity
7-14 days optimal harvest windowPlant reaches full size with firm, upright head; outer leaves are dark green and crispy, inner leaves are pale and tender
Maintain adequate water supply, monitor closely for bolting in heat, harvest outer leaves or entire head based on preference
Bolting
Variable, days to weeks depending on conditionsCentral stalk elongates rapidly, leaves become smaller and more bitter, flowers form; plant diverts energy to seed production
Harvest before bolting when possible; provide afternoon shade and consistent moisture to delay bolting in hot weather
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
-
Spray with water, use insecticidal soap, introduce ladybugs, apply neem oil for severe infestations
-
and
Hand-pick in early morning, use copper tape barriers, apply iron phosphate baits, encourage ground beetles
-
Remove affected leaves, use row covers on young plants, apply spinosad spray, encourage parasitic wasps
-
Use yellow sticky traps, spray with insecticidal soap, release parasitic wasps, improve air circulation
-
Use row covers on seedlings, apply kaolin clay, use neem oil, mulch to reduce beetle habitat
Uses
Caesar Salad & Fresh Cooking
CulinaryCos lettuce is the traditional choice for Caesar salads due to its crisp texture and sturdy leaves that hold dressing well. The elongated leaves are ideal for wraps, sandwiches, and any fresh salad preparation. [source]
Nutritious Greens
CulinaryRich in vitamins A, C, K, and folate, plus minerals like iron and calcium. Contains beneficial compounds like zeaxanthin and lutein that support eye health. [source]
Food Storage & Preservation
HouseholdCos lettuce stores well in refrigerator crisper for 1-2 weeks when kept dry. Can be blanched and frozen for cooking, or preserved through salting and dehydration methods. [source]
Garden Habitat Support
WildlifeWhen allowed to bolt, Cos lettuce flowers provide nectar and pollen for pollinators including bees and butterflies. Mature seeds feed birds and small wildlife. [source]
Traditional Wellness Support
MedicinalHistorically used in herbal preparations for its mild sedative properties and digestive support. Contains lactucarium, a compound with calming effects. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Harvest outer leaves individually once plant is 6-8 inches tall for extended harvests (cut-and-come-again method), or wait 55-75 days and harvest entire head by cutting 1 inch above soil line. Best harvested in cool morning hours when leaves are crisp and full of moisture. Heads are sweetest before bolting. For whole head harvest, cut through base with sharp knife.
Fun Facts
- 🌱 Cos lettuce is thought to be named after the Greek island of Cos, where it originated over 2,000 years ago, making it one of the oldest cultivated lettuce varieties.
- 🌱 The inner leaves of Cos lettuce naturally blanch (turn pale) as outer leaves shade them, creating the characteristic color gradient from dark green exterior to pale yellow heart without any special blanching techniques.
- 🌱 Cos lettuce was the preferred lettuce of the Romans, who valued it so highly that it appears in ancient Roman texts and artwork, and is believed to have been cultivated throughout the Roman Empire.
Gardening Terms
New to gardening? Learn about terms used in this guide:
Join 30,000 gardeners planning their gardens with LizPlants.
Get your personalized Cos Lettuce planting timeline
Tell us your zip code and we'll calculate exactly when to start Cos Lettuce seeds, transplant seedlings, and harvest — based on your USDA zone and local frost dates. Includes calendar reminders and printable task lists. Free to start.
Get my Cos Lettuce timeline →