Growing Romaine Lettuce in the US

Growing romaine lettuce

Romaine lettuce grows best in cool temperatures of 60–70°F. Plant 4–6 weeks before your last spring frost, or start a fall crop 8–10 weeks before first frost. It tolerates light frost but bolts quickly above 80°F.

Romaine — also called Cos lettuce — produces upright, elongated heads with thick ribs and crinkled leaves. It holds up better in heat than butterhead types, has a firmer texture than loose-leaf varieties, and is one of the most nutritious lettuces available. Growing it at home is straightforward once you understand the timing.

Planting times by USDA zone

Timing is the key to romaine success. This is a cool-season crop that runs out of time when summer arrives.

Fall crops are often larger and better-flavored than spring crops. Cooler, shortening days reduce bolt pressure. Fall crops also face fewer aphid and slug problems than spring crops in most US regions.

How to plant romaine lettuce

Starting from seed

Romaine germinates readily at soil temperatures of 60–65°F. Seeds germinate in 5–7 days at this temperature range.

Direct seeding:

1. Prepare bed with 2 inches of compost worked into the top 6 inches
2. Make rows ¼ inch deep and 12–18 inches apart
3. Sow seeds 1 inch apart in the row
4. Cover lightly with ¼ inch of fine soil
5. Water gently with a watering can; don’t wash seeds out of position
6. Keep soil consistently moist until germination (usually 5–7 days)
7. Thin to 6–8 inches between plants once seedlings reach 2 inches tall

Starting transplants indoors: Start seeds indoors under grow lights 4–6 weeks before transplant date. Use a soil-less seed starting mix in 2-inch cells. Lettuce seeds need light to germinate — press seeds onto the surface and cover with only 1/8 inch of mix. Transplant when seedlings reach 3–4 inches.

Transplanting

Harden transplants for 7 days before planting outdoors. Set transplants at the same depth they grew in the tray. Water in with liquid fertilizer diluted to half-strength.

Soil and fertilizer

Romaine is a heavy nitrogen feeder. It produces the most leaf growth when nitrogen is consistently available.

Soil preparation:

• Work in 2–3 inches of compost before planting
• Target pH of 6.0–7.0; most US soils are in this range
• Good drainage is critical — romaine in waterlogged soil develops root rot

Fertilizing schedule:

• At planting: top-dress with a balanced granular fertilizer (10-10-10 or similar) at the package rate
• 3 weeks after planting: side-dress with a nitrogen-focused fertilizer such as blood meal or fish emulsion
• Stop fertilizing 2 weeks before harvest to avoid excessive leaf softness

Watering romaine lettuce

Consistent moisture is essential. Irregular watering causes tip burn — brown, papery edges on inner leaves caused by calcium deficiency when water stress interrupts uptake.

Watering guidelines:

• Provide 1–1.5 inches of water per week
• Water at the base, not overhead — wet leaves invite fungal disease
• In summer heat, water every other day; in cool weather, every 3–4 days
• Mulch 2 inches around plants to retain soil moisture and moderate temperature

For more on efficient watering techniques, see drip irrigation system for low-labor setups in vegetable beds.

Managing heat and bolt prevention

Romaine bolts — sends up a flower stalk — when temperatures rise above 80°F and day length exceeds 14 hours. Once the bolt stalk begins rising, leaves become bitter within 3–5 days.

How to delay bolting:

• Use bolt-resistant varieties: ‘Parris Island Cos,’ ‘Jericho,’ ‘Coastal Star’
• Shade cloth (30–40% shade) reduces leaf temperature by 5–10°F during heat waves
• Water in the morning to cool the root zone
• Harvest at the first sign of the center stalk elongating — don’t wait for it to rise further

For detailed tips on growing lettuce through heat, see heat tolerant lettuce.

Romaine lettuce varieties

Different romaine varieties suit different climates and uses:

Pest and disease management

Aphids are the most common romaine pest in US gardens. They cluster on inner leaves and under leaf surfaces. Check plants twice weekly. A strong jet of water dislodges them. Neem oil spray applied in the evening is effective for larger infestations.

Slugs attack seedlings and young leaves. Beer traps placed near plants catch slugs overnight. See slug beer trap for setup instructions.

Downy mildew appears as yellow patches on upper leaf surfaces with gray fuzz below. Caused by cool, humid conditions and poor air circulation. Space plants at the recommended distance and avoid overhead watering.

Tip burn — brown edges on inner leaves — is a physiological problem, not a disease. Caused by calcium deficiency during irregular watering or heat stress. Maintain consistent soil moisture and choose tip burn-resistant varieties.

When and how to harvest

Romaine is ready for harvest 70–85 days from seed. Outer leaves can be harvested in as few as 30 days.

Three harvesting approaches:

1. Cut-and-come-again (outer leaves): Remove the outermost 2–3 leaves per plant, leaving the center growing point intact. Plants regrow outer leaves continuously. This extends harvest by 3–4 weeks beyond what a single cut allows.

2. Cut the whole head: Cut the head 1 inch above soil level. The stump often regrows a secondary head within 2–3 weeks in cool weather. Quality is good if soil remains moist and temperatures stay cool.

3. Pull the whole plant: Best if temperatures are rising toward bolt threshold and you want to use the full head before it turns bitter.

Storage: Romaine keeps 7–10 days refrigerated in a damp paper towel inside a plastic bag. Wash just before use, not before storage.

Succession planting for continuous harvest

Plant romaine in small batches every 2–3 weeks rather than all at once. A single seeding of romaine matures over a 3–4 week window. With succession planting, you have harvestable romaine over 6–8 weeks.

Example spring succession schedule (Zone 6):

• March 1: Sow batch 1 (indoor starts)
• March 15: Sow batch 2
• April 1: Transplant batch 1 outdoors
• April 15: Transplant batch 2; sow batch 3 direct
• May 1: Harvest batch 1 begins; sow batch 4 direct
• May 15: Harvest batch 2 begins; stop planting (heat risk rises)

For more information on growing lettuce year-round, see how to harvest lettuce and heat tolerant lettuce for summer alternatives. For companion plants that benefit lettuce beds, see lettuce companion plants.

According to the University of California Cooperative Extension, romaine is among the highest-yielding lettuce types per square foot in home gardens when grown in the correct season — producing 0.5–1 lb of edible leaves per plant per harvest.