Romaine lettuce
Lactuca sativa var. longifolia
Also known asCos lettuce · Roman lettuce · Cos
Environment
The bounded range this crop tolerates.
Climate and zones
- USDA zones
- 4–9 (winter low around -34°C)
- Frost
- tolerates light frost
- Season
- cool (spring/fall)
Growing systems
Root mass: light.
Growing media
| Medium | pH effect | Retention | Bacterial surface |
|---|---|---|---|
| Rockwool (Mineral wool) | alkaline until pre-soaked | very high | low |
| Expanded clay pebbles (LECA) | neutral / inert | low | high |
| Coco coir (Coconut coir) | slightly acidic | high | moderate |
| Net pot, no medium (Bare-root) | - | - | - |
| Soil-based mix (Potting soil) | varies | high | high |
Nutrient demand by stage
NPK ratios are relative weights. EC targets shift through the plant's life.
| Stage | N | P | K | EC (mS/cm) |
|---|---|---|---|---|
| seedling | 1 | 1 | 1 | 0.6 |
| vegetative | 3 | 1 | 2 | 1.2 |
Aquaponics suitability
Compatible
Fish waste provides enough nitrogen for healthy growth. Supplemental potassium, calcium, and iron may still be needed depending on fish stocking density.
Care notes
A standard hydroponic lettuce type, slightly more challenging than loose-leaf but easier than iceberg. EC 0.8-1.5 mS/cm. pH 5.5-6.5. Temperature: 15–22°C (cool-season; above 24°C, bolting begins and the leaves become bitter). Moderate light (DLI 12-17 mol/m2/day). NFT, DWC, raft, or vertical systems. From seed to full head: 7-9 weeks. Baby romaine (harvested young as individual leaves): 4-5 weeks. The upright head formation requires slightly more space per plant than loose-leaf types. Tipburn on inner leaves is possible in warm, still conditions; improve airflow and maintain calcium levels. For commercial growers, romaine hearts (trimmed, bagged inner portions) are a premium product ($3-5 per head). The food safety advantage of hydroponic romaine (no soil contact, no irrigation water contamination) is a genuine selling point in markets that have experienced recall anxiety from Salinas Valley outbreaks.