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 | March – April | April – May | April – August | June – October |
| Zone 4 | March – April | April – May | April – August | June – October |
| Zone 5 | February – April | March – May | March – August | May – November |
| Zone 6 | February – March | March – April | March – September | May – November |
| Zone 7 | January – March | February – April | February – September | April – December |
| Zone 8 | January – February | February – March | February – October | April – December |
| Zone 9 | December – February | January – March | January – November | March – January |
| Zone 10 | November – January | December – February | December – November | February – January |
Complete Growing Guide
Start your Romaine Cos seeds indoors 4-6 weeks before your last frost date, or direct sow in early spring when soil temperatures reach 45-50°F. This variety performs best in cool weather, so timing is crucial for success.
Prepare your planting bed by working in 2-3 inches of well-aged compost or aged manure to a depth of 8-10 inches. Romaine Cos demands excellent drainage—standing water will kill seedlings within days. If your soil is heavy clay, create raised beds or add coarse sand and compost to improve drainage. Test your soil pH and aim for 6.0-6.8; this variety struggles in acidic conditions.
When direct seeding, plant seeds 1/4 inch deep in rows spaced 12-15 inches apart. Thin seedlings ruthlessly when they reach 2 inches tall—overcrowding leads to weak, bolt-prone plants. Give each plant 8-10 inches of space in all directions. If starting indoors, use individual cells or small pots since lettuce roots are easily damaged during transplanting.
Fertilize with a balanced 10-10-10 fertilizer at planting, then side-dress with nitrogen-rich fertilizer (like fish emulsion) every 3 weeks. Avoid high-nitrogen feeds in hot weather as they promote bolting.
The biggest mistake gardeners make is planting too late in spring or trying to grow this variety in summer heat. In zones 7-9, plant your main crop in fall for winter harvest—the flavor actually improves in cool weather. Northern gardeners should succession plant every 2 weeks through early summer.
Consistent moisture is critical, but avoid overhead watering which promotes disease. Use drip irrigation or soaker hoses, and water deeply twice weekly rather than daily shallow watering. Mulch around plants with straw to retain moisture and suppress weeds, but keep mulch 2 inches away from stems to prevent rot.
Harvesting
Harvest Romaine Cos when heads reach 8-10 inches tall and feel firm when gently squeezed from the sides. The outer leaves should be deep green with prominent white ribs, while inner leaves remain pale yellow-green. Perform the 'squeeze test'—mature heads feel solid and compact, not loose or spongy.
Cut in early morning when plants are fully hydrated and crisp. Use a sharp knife to slice through the base just above soil level, leaving the root system intact. If you notice the center beginning to elongate or flower buds forming, harvest immediately as the leaves will turn bitter within days.
You can also harvest outer leaves continuously once plants reach 6 inches tall, allowing the center to continue growing. This method extends your harvest window by 3-4 weeks. Always harvest before temperatures consistently reach 75°F, as heat causes rapid bolting and bitter flavors.
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
Romaine lettuce originated on the Greek island of Cos (modern-day Kos) over 2,000 years ago, giving it the alternative name 'Cos lettuce.' Ancient Romans cultivated this variety extensively throughout their empire, prizing its ability to withstand transport and storage—crucial for feeding armies on long campaigns.
The variety reached peak popularity during the Renaissance when Italian monks refined the growing techniques and selected for the characteristic upright growth habit and crisp texture. French gardeners adopted Romaine in the 17th century, and it became essential in haute cuisine.
Romaine Cos gained worldwide fame as the original lettuce for Caesar salad, created in 1924 by Caesar Cardini in Tijuana, Mexico. The variety's sturdy leaves and slightly bitter flavor provided the perfect foundation for the rich dressing. Today's Romaine Cos maintains the same genetic characteristics as ancient varieties, making it a true culinary heirloom that connects modern gardeners to thousands of years of cultivation history.
Advantages
- +Exceptional heat tolerance compared to other lettuce varieties, extending growing season by 2-3 weeks
- +Self-blanching heads create tender, pale yellow hearts without manual intervention
- +Sturdy leaf structure holds dressings exceptionally well without wilting
- +Naturally upright growth habit requires no staking or support systems
- +Superior storage life of 7-10 days in refrigeration due to robust leaf structure
- +Authentic variety essential for traditional Caesar salad preparation
- +Performs well in both spring and fall plantings across most climate zones
Considerations
- -Long 70-85 day maturity period requires significant garden space commitment
- -Highly susceptible to bottom rot in poorly drained soils or wet conditions
- -Bolts rapidly once temperatures exceed 75°F consistently
- -More challenging to grow than loose-leaf varieties, requiring precise timing and spacing
- -Susceptible to tipburn in hot, dry conditions despite overall heat tolerance
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
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