Romaine lettuce (Lactuca sativa var. longifolia) is a popular variety of leafy green prized for its crisp texture, upright growth habit, and distinctive elongated leaves with a firm, pale central rib. Leaves range from medium to dark green and carry a mildly bitter yet refreshing flavour that holds up well in hearty salads and cooked dishes alike.

Unlike softer heading lettuces, romaine maintains its structure after dressing, making it the classic choice for Caesar salad and lettuce wraps. It is low in calories yet nutritionally dense, providing excellent levels of vitamins A, C, and K, along with folate, potassium, and dietary fibre. The outer leaves are darker and more nutrient-rich, while the inner pale leaves offer a sweeter, more tender bite.

Romaine is a cool-season crop that performs best in mild temperatures and can tolerate light frosts, making it suitable for both spring and autumn growing. It can be grown from seed directly in the ground or started under cover and transplanted, offering flexibility for gardeners in a variety of climates.

How To Grow

Soil & Site

Romaine lettuce thrives in fertile, well-drained soil rich in organic matter, with a pH between 6.0 and 6.8. Improve poor soils by incorporating well-rotted compost before planting. Choose a position in full sun or partial shade — light shade is beneficial in warmer periods to slow bolting.

Sowing

• Direct sowing: Sow seeds approximately 0.6 cm deep, thinning seedlings to 20 cm apart once established.
• Indoor sowing: Start seeds in trays or modules 3–4 weeks before transplanting outdoors. Harden off seedlings gradually before planting out.
• Succession sowing: Sow small batches every 2–3 weeks for a continuous harvest throughout the season.
• Seeds typically germinate within 7–14 days at soil temperatures of 7–24°C.

Watering & Feeding

Keep the soil consistently moist but not waterlogged. Lettuce has shallow roots and will wilt quickly without regular watering. Apply a mulch layer around plants to retain moisture and keep the root zone cool. Feed with a balanced, nitrogen-rich fertiliser to encourage leafy growth, particularly in poorer soils.

Temperature

Romaine is a cool-season crop that grows best between 7°C and 24°C. It can tolerate light frosts but will bolt (go to seed) rapidly in prolonged heat above 25°C. In warm seasons, choose bolt-resistant varieties and provide afternoon shade where possible.

Harvesting

When to Harvest

Romaine lettuce is typically ready to harvest 60–75 days after sowing, when heads are firm and upright, reaching approximately 15–20 cm in height. Harvest before the plant begins to bolt — a sure sign of bolting is when the central stem starts to elongate rapidly and leaves become bitter.

Harvesting the Whole Head

1. Use a sharp, clean knife or garden shears.
2. Cut the stem at the base, just above soil level.
3. Leaving the root undisturbed may encourage a secondary flush of smaller leaves in some conditions.

Cut-and-Come-Again Method

For a longer, ongoing harvest, use the cut-and-come-again technique:

1. Begin harvesting outer leaves once they are large and well-developed, usually 30–40 days after sowing.
2. Cut or snap leaves cleanly approximately 2–3 cm above the base — do not pull, as this can disturb roots.
3. Leave the central growing point and inner leaves intact to continue producing.
4. Repeat every 1–2 weeks for multiple harvests from each plant.

Storage

Freshly harvested romaine keeps well in the refrigerator for up to one week. Store unwashed in a loosely sealed bag or container with a little moisture to maintain crispness.

Common Problems

Common Pests

Aphids Aphids cluster on the undersides of leaves, causing curling, yellowing, and stunted growth. Blast them off with a jet of water, introduce natural predators such as ladybirds, or apply an insecticidal soap spray.

Slugs & Snails These are among the most damaging pests for lettuce, particularly on young seedlings. Use physical barriers such as copper tape, apply organic slug pellets, or set beer traps around plants.

Cutworms & Caterpillars Larvae can sever young stems at soil level overnight. Check around the base of plants and remove larvae by hand. Use fine mesh netting to exclude adult moths and butterflies.

Lettuce Root Aphid This less visible pest attacks the roots, causing sudden wilting. Crop rotation and resistant varieties are the most effective prevention strategies.

Common Diseases

Downy Mildew Appears as yellow patches on upper leaf surfaces with grey-white mould beneath. Improve air circulation by spacing plants well and avoid overhead watering. Remove and dispose of affected leaves promptly.

Grey Mould (Botrytis) Fuzzy grey mould develops in cool, humid, poorly ventilated conditions. Remove infected material immediately and avoid wetting foliage when watering.

Tip Burn Brown, scorched leaf edges caused by calcium deficiency or irregular watering in warm conditions. Maintain consistent soil moisture and avoid excessive heat.