Loose-leaf lettuce
Lactuca sativa var. crispa
Also known asSalad bowl lettuce · Leaf lettuce · Cutting lettuce
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 | 1.1 |
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
The default hydroponic lettuce type and one of the most commonly grown hydroponic crops worldwide. EC 0.8-1.5 mS/cm. pH 5.5-6.5. Temperature: 15–22°C ideal (loose-leaf types tolerate 24–26°C slightly better than heading types before bolting, though summer heat remains the primary challenge). Moderate light (DLI 12-17 mol/m2/day; high DLI above 20 causes bitterness and bolting). From seed to baby leaf harvest: 3-4 weeks. Full-sized harvest: 5-6 weeks. NFT, DWC, raft, Kratky, and vertical tower systems all work. Cut-and-come-again harvesting (taking outer leaves while the center continues growing) extends each planting's productive life to 4-6 weeks of continuous harvest. Succession plant weekly for uninterrupted supply. Red varieties need slightly more light than green types to develop full color. Tipburn is less common in loose-leaf types than in heading lettuce because airflow reaches the inner leaves. For commercial growers, a mix of red, green, and specialty varieties allows premium salad mix pricing ($8-15/kg retail). Loose-leaf lettuce is the best crop for beginners learning hydroponic growing.
Notable varieties
| Cultivar | Type | Days | Notes |
|---|---|---|---|
| Black Seeded Simpson | heirloom | 45 | Pre-1850 heirloom, light green frilly leaves. One of the earliest spring lettuces. Bolts quickly in heat; cool-season only in zone 7+. Cut-and-come-again productive. |
| Red Sails | open pollinated | 55 | 1985 All-America Selections winner. Deep red-bronze ruffled leaves. Slower to bolt than Black Seeded Simpson, useful for stretching the season into early summer. Mild flavor, beautiful in mixed salads. |
| Salad Bowl | open pollinated | 50 | 1952 AAS winner. Light green deeply lobed oak-leaf-shaped leaves. Slow bolting in heat. Cut-and-come-again productive over 8-10 weeks if temperatures stay below 25C. |
| Lollo Rossa | open pollinated | 55 | Italian frilly loose-leaf with intensely curled magenta-edged leaves. Slightly bitter flavor balances milder lettuces in a mix. Heat-tolerant compared to most loose-leafs. |