Climate matters. This page is a practical baseline. Confirm cultivar, local frost/heat conditions, mature size and regional restrictions before planting.
Romaine Lettuce — Growing reference
| Scientific name | Lactuca sativa var. longifolia |
|---|---|
| Seed germination (days) | 2–10 |
| Soil temperature for germination (°C) | 4.4–23.9 |
| First harvest or flowering (days) | 60–80 |
| Measured from | Seed |
| Plant spacing (cm) | 20.3–30.5 |
| Mature height (cm) | 20.3–45.7 |
| Mature spread (cm) | 20.3–30.5 |
| USDA hardiness zones | 2–11 |
| Light | Partial sun |
| Water | Moderate |
| Sowing method | Direct sow |
Growing directions
Sow seed at 1/8 in depth in cool soil and thin to 8–12 in; romaine forms an upright, elongated head that needs slightly more space than loose-leaf types. Keep soil evenly moist to prevent tip burn, which appears as brown leaf edges due to calcium deficiency from moisture stress. Harvest by cutting the whole head at soil level when it is 8–10 in tall and the inner leaves feel firm. Outer leaves can be removed individually as the head develops to extend the harvest period.
Source and local conditions
Typical planning ranges from OpenPlantDB (CC0). Cultivar, climate, season and growing method can change these values. Confirm the seed label and local guidance before planting.
Source & verification
OpenPlantDB · CC0