Romaine Lettuce or Cos
Planting, Growing, and Harvesting
Romaine Lettuce or Cos
You’ll find everything you need to know to plant and grow romaine lettuce or cos in the accompanying table’s tabs:
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- How many romaine lettuce or cos plants to grow
- Growing conditions for romaine lettuce or cos
- When to plant romaine lettuce or cos
- How to plant romaine lettuce or cos
- Watering, fertilizing, and pruning romaine lettuce or cos
- Companion plantings for romaine lettuce or cos
- How to harvest, store, and use romaine lettuce or cos
Growing Romaine Lettuce or Cos
Romaine lettuces are many different varieties of Cos (Lactuca sativa var. longifolia), semi-headed, cool-season leafy-green vegetables. Romaine has oval, light green leaves with prominent ribs and veins. It forms upright plants, 8–9 in. (20–23 cm) tall, with loosely open, cylindrical or oval heads.
Green yellow central leaves are tender, crisp, and sweeter than both the outer leaves and other cultivars. Romaine’s tender and crunchy leaves are perfect for Caesar salads. Choose dwarf cultivars for planting in containers, small-space gardens. Some Cos varieties tolerate heat that cause other lettuce varieties to bolt.
Celtuce (asparagus lettuce) is a closely related species with similar habits [see: Celtuce or Asparagus Lettuce].
Romaine Lettuce or Cos Plant Guide
How Much to Plant
Allow 6–10 plants per household member.
How to Plant
Seed germinates in 7–10 days.
Average Climates: Sow seed indoors 4–6 weeks before last expected frost and harden seedlings 4–5 days before transplanting, or in late summer or early autumn.
Mild-Winter Climates: Sow seed or transplant seedlings in full sun in winter.
Autumn–Winter Gardens: Sow seed from May–October or transplants from June–October for harvest in autumn–winter.
Set out seedlings 3–4 in. (75–100 mm) tall when soil warms to 40–75°F (4–24°C).
Sow seed 1/4–1/2-in. (6–12 mm) deep, 1–2 in. (25–50 mm) apart, thinning to 6–8 in. (15–20 cm) apart, in rows 16–24 in. (40–60 cm) apart.
Alternatively broadcast seed over an area and thin sprouts after germination to 10 in. (25 cm) apart.
Avoid overcrowding; best in small, separated plantings. Plant successions every 3–5 weeks.
Best Conditions for Growth
Growing temperature: 45–75°F (7–24°C). Shade plants at temperatures above 85°F (29°C). Bolts in temperatures over 80°F (27°C) and when daylight hours lengthen in summer. Most heat-tolerant lettuce species.
Soil Type and Fertility
Moist, well-drained, sandy soil. Fertility: Rich. 6.0–6.8 pH. Prepare soil at least 1 ft. (30 cm) deep.
Proper Care
Easy. Keep evenly moist; avoid wetting foliage. Apply ample water during the head-development stage. Fertilize only at planting with 5–10–10 formula. Mulch. Cultivate. Blanch romaine to ensure white lower leaves when 6 in. (15 cm) tall by wrapping with opaque, waterproof paper. Chewing insect and slug, snail susceptible.
Autumn–Winter Gardens: Protect from frost and freezes beginning in October.
Pairing Recommendations
Carrots, corn, cucumbers, radishes, and strawberries.
Maturity, Picking and Gathering
80–85 days. Cut stem 1 in. (25 mm) above the soil when 8 in. (20 cm) tall, leaving the central growth bud to resprout. Immerse cut romaine in ice water immediately after cutting.
How to Store and Preserve
Fresh in vegetable keeper of refrigerator for 2–3 weeks. Good eaten raw as leafy green in salads. Dry leaves thoroughly after rinsing and tear romaine into bite-sized pieces; water dilutes the flavors of both the lettuce and most salad dressings. The lettuce of choice to combine with coddled eggs, anchovies, Parmesan cheese, croutons and seasonings in assembling Caesar salads. Also may be used fresh or steamed as wrap over ground-meat and vegetable fillings as for cabbage rolls and Asian summer rolls.