Romaine Cos
Lactuca sativa var. longifolia 'Cos'
The classic upright lettuce that forms tall, sturdy heads of dark green leaves with prominent white ribs and exceptional crunch. This traditional variety has been cultivated for over 2,000 years and remains the gold standard for Caesar salads and Mediterranean cuisine. Its robust structure and intense flavor make it indispensable for gardeners who want restaurant-quality lettuce at home.
Harvest
70-85d
Days to harvest
Sun
'Allstar Mix'
Zones
2–11
USDA hardiness
Height
6-12 inches
Planting Timeline
Showing dates for Romaine Cos in USDA Zone 7
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Romaine Cos · Zones 2–11
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | — | — | May – June | July – October |
| Zone 4 | — | — | April – June | July – October |
| Zone 5 | — | — | April – May | July – November |
| Zone 6 | — | — | April – May | June – November |
| Zone 7 | — | — | March – May | June – November |
| Zone 8 | — | — | March – April | May – December |
| Zone 9 | — | — | February – March | April – December |
| Zone 10 | — | — | January – March | April – December |
Complete Growing Guide
Light: 'Allstar Mix', 'Bibb', 'Black-seeded Simpson', 'Buttercrunch', 'Green Oakleaf', 'Ithaca', 'Jericho', Lactuca sativa var. augustana ('Celtuce'), 'New Red Fire', 'Pennlake', 'Red Sails', 'Salinas'. Soil: High Organic Matter. Soil pH: Neutral (6.0-8.0). Drainage: Good Drainage, Moist. Height: 0 ft. 6 in. - 1 ft. 0 in.. Spread: 0 ft. 6 in. - 1 ft. 0 in.. Spacing: Less than 12 inches. Growth rate: Rapid. Maintenance: Medium. Propagation: Seed. Regions: Coastal, Mountains, Piedmont.
Harvesting
Tiny seeds with a dandelion-like tuft (pappus) to aid in wind dispersal.
Color: Brown/Copper. Type: Achene. Length: < 1 inch. Width: < 1 inch.
Harvest time: Summer
Bloom time: Summer
Edibility: Leaves can be used raw or cooked in salads, sandwiches, and other dishes. Head lettuce can be stored for 2-3 weeks while leaf and butterhead store for 1-2 weeks.
Storage & Preservation
Store freshly harvested Romaine Cos in the refrigerator crisper drawer, wrapped loosely in damp paper towels inside a perforated plastic bag. Properly stored heads maintain quality for 7-10 days, significantly longer than most lettuce varieties due to their sturdy structure.
For best flavor and texture, use within 5 days of harvest. Wash leaves just before use, never before storage, as excess moisture accelerates decay.
Romaine Cos isn't suitable for traditional preservation methods like freezing or canning due to its high water content. However, you can dehydrate outer leaves at 135°F to create crispy lettuce chips, or ferment chopped leaves with salt to make a tangy condiment similar to sauerkraut. The robust leaves also work well in quick refrigerator pickles when combined with vinegar and spices.
History & Origin
Origin: Mediterranean to Siberia
Advantages
- +Edible: Leaves can be used raw or cooked in salads, sandwiches, and other dishes. Head lettuce can be stored for 2-3 weeks while leaf and butterhead store for 1-2 weeks.
- +Fast-growing
Considerations
- -Toxic (Sap/Juice): Low severity
- -Causes contact dermatitis
Companion Plants
Plant Together
Chives
Repels aphids and improves lettuce flavor while providing natural pest deterrent
Carrots
Deep roots don't compete with shallow lettuce roots, maximizes garden space efficiently
Radishes
Quick-growing companion that loosens soil and deters flea beetles
Marigolds
Repels aphids, whiteflies, and other pests that commonly attack lettuce
Dill
Attracts beneficial insects like ladybugs and lacewings that control aphids
Garlic
Natural fungicide properties help prevent lettuce diseases and repel pests
Nasturtiums
Acts as trap crop for aphids and cucumber beetles, protecting lettuce
Spinach
Similar growing requirements and harvesting times, efficient space utilization
Parsley
Attracts beneficial insects and provides ground cover without competing for nutrients
Keep Apart
Broccoli
Heavy feeder that competes for nutrients and may shade lettuce excessively
Fennel
Releases allelopathic compounds that inhibit growth of lettuce and most vegetables
Sunflowers
Allelopathic effects suppress lettuce growth and tall plants create excessive shade
Nutrition Facts
Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #169247)
Pests & Disease Resistance
Resistance
Moderate resistance to tipburn, susceptible to bottom rot in wet conditions
Common Pests
Aphids, leafminers, cutworms, flea beetles
Diseases
Downy mildew, bottom rot, tipburn, bacterial leaf spot