Paris Island Cos
Lactuca sativa 'Paris Island Cos'
The gold standard for romaine lettuce, this heat-tolerant variety produces tall, upright heads with crisp, dark green outer leaves and sweet, crunchy hearts. Developed for reliability in challenging conditions, Paris Island Cos consistently delivers the classic romaine experience that Caesar salad lovers crave. Its exceptional bolt resistance makes it perfect for extending the growing season into warmer months.
Harvest
66-75d
Days to harvest
Sun
Full sun to partial shade
Zones
2–11
USDA hardiness
Height
6-12 inches
Planting Timeline
Showing dates for Paris Island Cos in USDA Zone 7
All Zone 7 lettuce →Zone Map
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Paris Island 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 | June – November |
| Zone 6 | — | — | April – May | June – November |
| Zone 7 | — | — | March – May | May – November |
| Zone 8 | — | — | March – April | May – December |
| Zone 9 | — | — | February – March | April – December |
| Zone 10 | — | — | January – March | March – December |
| Zone 1 | — | — | June – July | August – September |
| Zone 2 | — | — | May – July | July – September |
| Zone 11 | — | — | January – February | February – December |
| Zone 12 | — | — | January – February | February – December |
| Zone 13 | — | — | January – February | February – December |
Succession Planting
Direct sow Paris Island Cos every 14 days starting March 1 in zone 7, and keep sowing through late April. At 66-75 days to maturity, anything started after mid-May will be heading up right when daytime highs crack 85°F — the plants bolt and turn bitter before the heads are worth cutting. Pick it back up in late August for a fall run; sow through mid-September and you'll be pulling heads well into November. There's no trick to pushing this variety through summer — it just doesn't work, and the bolt-to-harvest window collapses too fast to bother.
Complete Growing Guide
Paris Island Cos thrives when direct sown in the garden about two weeks before your last spring frost, or you can start seeds indoors three to four weeks prior and transplant seedlings out once they've developed their first true leaves. This variety's heat tolerance makes it an excellent candidate for succession plantings every two weeks throughout spring and into early summer, allowing you to harvest fresh romaine well beyond the typical spring window when many other varieties have bolted. For fall crops, sow seeds in mid to late summer to mature as temperatures cool.
Prepare your soil with plenty of organic matter worked into the top six inches, as Paris Island Cos appreciates rich, well-draining conditions that retain moisture without becoming waterlogged. Space seeds or transplants about eight inches apart in rows twelve inches apart, planting seeds a quarter-inch deep. This spacing allows the variety's tall, upright heads to develop fully without crowding, which can promote the fungal diseases this cultivar is prone to in humid conditions.
Water consistently throughout the growing season, providing about one inch per week through rainfall or irrigation. Keep the soil evenly moist but never soggy, as oversaturation combined with the variety's susceptibility to bottom rot and lettuce drop creates ideal disease conditions. Morning watering is preferable to evening watering, as it allows foliage to dry quickly. Feed with a balanced, nitrogen-rich fertilizer every three weeks once seedlings are established, as Paris Island Cos is a vigorous grower that benefits from consistent nutrition.
Watch vigilantly for aphids and thrips, which are particularly problematic for this variety in warm weather and can quickly colonize the tightly bunched hearts. Regular inspection of leaf undersides catches infestations early. Cabbage worms may also appear; row covers during establishment help prevent egg-laying. Slugs favor the tender outer leaves, so manage them through mulch removal near the base and evening hand-picking if populations are light.
Disease pressure increases as temperatures warm, making Paris Island Cos's bolt resistance especially valuable but also requiring attention to fungal threats. Tipburn, caused by calcium deficiency exacerbated by inconsistent watering, appears as brown spots on inner leaves; prevent it through steady moisture and adequate spacing for air circulation. Downy mildew appears as pale patches on foliage and requires immediate removal of affected leaves and improved air flow. Lettuce drop and bottom rot are bacterial diseases that typically appear in cool, wet conditions; remove infected plants immediately to prevent spread.
Many gardeners overlook that Paris Island Cos needs consistent air circulation to prevent fungal problems, especially as heads tighten. Avoid overcrowding and thin seedlings promptly rather than allowing them to compete for resources in dense patches. This simple practice makes the difference between consistent success and disappointing disease losses with this otherwise reliable variety.
Harvesting
Harvest Paris Island Cos when the heads reach 6 to 12 inches tall and feel firm and compact to gentle hand pressure, with outer leaves displaying that characteristic dark green color and the inner heart showing pale, tender leaves. Cut individual heads at the base with a sharp knife once they've achieved full size and before the central stem begins to elongate, which signals bolting. For continuous harvests, remove outer leaves from mature plants and allow the center to regenerate for secondary harvests, or stagger plantings two weeks apart. Time your main harvest in early morning when temperatures are cool and leaves are fully hydrated for maximum crispness and shelf life.
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
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 Paris Island Cos in the refrigerator immediately after harvest for maximum shelf life. Wrap whole heads loosely in damp paper towels, then place in perforated plastic bags in the crisper drawer — this maintains the 95% humidity lettuce needs while preventing condensation buildup. Properly stored heads keep 7-10 days.
For longer preservation, this variety's sturdy leaves make excellent candidates for dehydrating into lettuce chips or powdering for seasoning blends. Blanch outer leaves for 30 seconds before freezing for use in cooked dishes and smoothies, though texture will be soft after thawing. The dense, crunchy hearts can be pickled whole in light brine solutions, creating a unique preserved vegetable that maintains much of its characteristic crunch for 2-3 months refrigerated.
History & Origin
Paris Island Cos emerged from the American seed company Harris Seeds, which introduced this romaine selection in the mid-20th century as part of broader efforts to develop reliable lettuce varieties for commercial cultivation. The variety descends from the broader Cos (or Romaine) lettuce lineage, which traces its ancestry to Mediterranean heirloom populations. Harris Seeds specifically bred Paris Island Cos to emphasize heat tolerance and bolt resistance—traits essential for extending harvest windows beyond spring and early summer. While detailed breeder names and exact development years remain sparsely documented in publicly available sources, the variety's consistent performance and widespread adoption across North American gardens and farms reflect successful selection for stability and reliable performance in variable growing conditions.
Origin: Mediterranean to Siberia
Advantages
- +Exceptional heat tolerance allows extended harvesting into warm summer months
- +Reliable bolt resistance provides consistent yields across diverse growing conditions
- +Tall upright heads with dark green leaves offer striking visual appeal
- +Sweet, crunchy hearts deliver classic Caesar salad quality that restaurants prefer
- +Developed for challenging conditions, Paris Island Cos proves remarkably dependable overall
Considerations
- -Susceptible to tipburn when calcium uptake fluctuates from inconsistent watering
- -Requires vigilant pest management against aphids, cabbage worms, slugs, and thrips
- -Vulnerable to downy mildew and lettuce drop in humid growing environments
Companion Plants
Chives and garlic at the bed edges pull real duty against aphids — the sulfur compounds those alliums release disrupt how aphids locate host plants, and aphids are the steadiest pest pressure Paris Island Cos faces. Radishes tucked in every few feet germinate in 5-7 days, mark your rows before the lettuce fills in, and discourage flea beetles from settling in. Marigolds (Tagetes species) draw predatory wasps that keep cabbage worm numbers down. Broccoli is worth keeping at least 3 feet away — it competes in the same shallow moisture zone and acts as a cabbage worm reservoir. Black walnut is a hard no anywhere nearby; juglone in the soil will stunt or kill lettuce before you figure out what's wrong.
Plant Together
Chives
Repels aphids and improves lettuce flavor while providing natural pest deterrent
Marigolds
Repels nematodes, aphids, and other harmful insects that damage lettuce
Carrots
Grows well in similar soil conditions and helps break up soil for lettuce roots
Radishes
Quick-growing companion that helps break up soil and can be harvested before lettuce needs full space
Nasturtiums
Acts as trap crop for aphids and cucumber beetles, protecting lettuce
Dill
Attracts beneficial insects like ladybugs and lacewings that control lettuce pests
Spinach
Similar growing requirements and can be interplanted for efficient space usage
Garlic
Repels aphids, slugs, and other pests that commonly attack lettuce
Keep Apart
Broccoli
Competes heavily for nitrogen and can shade out lettuce with its large leaves
Sunflowers
Produces allelopathic compounds that inhibit lettuce germination and growth
Walnut Trees
Releases juglone, a natural herbicide toxic to lettuce and most vegetables
Nutrition Facts
Per 100g serving. % Daily Value based on 2,000 calorie diet. Source: USDA FoodData Central (FDC #2346388)
Pests & Disease Resistance
Resistance
Good heat tolerance and bolt resistance
Common Pests
Aphids, cabbage worms, slugs, thrips
Diseases
Tipburn, downy mildew, lettuce drop, bottom rot
Troubleshooting Paris Island Cos
What you'll see, why it happens, and what to do about it.
Seedlings collapse and die within 7-10 days of going in the ground, sometimes with a fuzzy whitish mold on the soil surface
Likely Causes
- Damping off — a fungal complex (commonly Pythium or Rhizoctonia solani) that thrives in cold, wet, poorly drained soil
- Replanting the same bed with lettuce for 3+ consecutive seasons, allowing pathogen load to build up
What to Do
- 1.Don't reuse the same bed for lettuce more than two seasons running — rotate to a different spot
- 2.Improve drainage before planting: work in compost and raise the bed if needed; don't water in the evening
- 3.If you're starting seeds indoors, use fresh, sterile seed-starting mix — not garden soil
Leaf edges turning brown and papery, starting on the innermost leaves of the head around day 50-60
Likely Causes
- Tipburn — a calcium deficiency in the tissue caused by poor internal water movement, not a shortage of calcium in the soil
- Inconsistent watering or low humidity that slows transpiration in the tightly wrapped inner leaves
What to Do
- 1.Water consistently — 1 to 1.5 inches per week, never letting the soil go completely dry between waterings
- 2.Cut heads at 66-70 days rather than waiting for maximum size; Paris Island Cos held too long in warming weather tipburns fast
- 3.Thin to 8-10 inches apart so inner leaves aren't trapped in stagnant air between crowded plants
White to grayish fuzzy growth on the undersides of leaves, with yellow patches visible on the upper surface
Likely Causes
- Downy mildew (Bremia lactucae) — a water mold that spreads quickly in cool, humid conditions with poor airflow
- Overhead irrigation or rain that keeps foliage wet overnight, especially in dense plantings
What to Do
- 1.Pull and trash affected leaves immediately — do not compost them, as Bremia lactucae spreads by spores
- 2.Water at the base of plants in the morning so foliage dries before nightfall; drip tape is better than a sprinkler for this crop
- 3.Space plants the full 8-10 inches apart; rows packed tighter than that create the damp, still air this pathogen needs
Frequently Asked Questions
How long does Paris Island Cos lettuce take to grow?▼
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Growing Guides from Wind River Greens
Where to Buy Seeds
Sources & References
External authority sources used in compiling this guide.
See the Methodology page for how this data is sourced, what's AI-assisted, and known limitations.