How to Grow Romaine Cos
Lactuca sativa var. longifolia 'Cos'
Romaine Cos lettuce is a beloved heirloom variety prized for its tall, upright heads and crisp, buttery texture. Gardeners choose this cool-season crop to enjoy fresh salads during spring and fall when temperatures are mild enough to prevent bitterness.
Starting Romaine Cos: indoors or direct sow?
🌾 Sow directly in the garden — Romaine Cos is not usually started indoors.
This plant is best direct-sown in the garden rather than started indoors and transplanted later.
Soil, care & harvest
Prepare loose, well-draining soil with a pH between 6.0 and 7.0 for optimal growth. As a cool-season crop, sow seeds directly outdoors or start indoors two to six weeks before your last expected spring frost. Press seeds gently into the soil at a depth of about one-quarter inch. You can expect germination within seven to ten days under these conditions.
Space plants eight to twelve inches apart to allow their tall heads room to develop fully without crowding. While this variety does not require trellising, consistent moisture is vital; aim for one to one-and-a-half inches of water per week via deep watering. Apply a light layer of mulch around the base to retain soil moisture and suppress weeds.
Monitor your plants for aphids, leafminers, cutworms, and flea beetles, treating infestations early with hand-picking or organic sprays. Watch closely for downy mildew, bottom rot in wet spots, tipburn, and bacterial leaf spot by ensuring good air circulation. Harvest heads when they reach maturity, typically seventy to eighty-five days after sowing, cutting them at the base.
When to Plant Romaine Cos
Planting windows vary by USDA hardiness zone. Look up yours by ZIP code.
| Zone | Start Indoors | Direct Sow | Harvest |
|---|---|---|---|
| Zone 1 | — | June – July | August – September |
| Zone 2 | — | May – July | August – September |
| 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 |
| Zone 11 | — | January – February | March – December |
| Zone 12 | — | January – February | March – December |
| Zone 13 | — | January – February | March – December |
Companion Plants for Romaine Cos
✓ Good companions
Deep roots don't compete with shallow lettuce roots, maximizes garden space efficiently
Repels aphids and improves lettuce flavor while providing natural pest deterrent
Attracts beneficial insects like ladybugs and lacewings that control aphids
Natural fungicide properties help prevent lettuce diseases and repel pests
Repels aphids, whiteflies, and other pests that commonly attack lettuce
Acts as trap crop for aphids and cucumber beetles, protecting lettuce
Attracts beneficial insects and provides ground cover without competing for nutrients
Quick-growing companion that loosens soil and deters flea beetles
Similar growing requirements and harvesting times, efficient space utilization
✗ Keep away from
Heavy feeder that competes for nutrients and may shade lettuce excessively
Releases allelopathic compounds that inhibit growth of lettuce and most vegetables
Allelopathic effects suppress lettuce growth and tall plants create excessive shade
Nutrition Facts
Per 100g serving (USDA FoodData Central)
