Lettuce
Lettuce-specific crop notes stay here; shared crop counts, active-control status, vision context, and stress panels live on the crop overview pages.
The anchor crop. Fast rotation, high demand, loves the East Zone’s cooler temperatures. Late May is the transition out of the easiest lettuce window; the south zone is already too hot, and even the east zone starts pushing lettuce’s comfort range.
Optimal Conditions
| Parameter | Range | Notes |
|---|---|---|
| Day temperature | 65-75°F | Above 80°F triggers bolting |
| Night temperature | 55-65°F | Cool nights improve crispness |
| VPD | 0.8-1.0 kPa | Moderate — lettuce transpires freely |
| DLI | 14-17 mol/m²/d | Below 12 = leggy. Above 20 = can trigger bolting with heat |
| pH (hydro) | 5.5-6.0 | Slightly acidic |
| EC | 0.8-1.2 mS/cm | Light feeder |
| Photoperiod | 14-16 hours | Day-neutral but benefits from long days |
Control Target Source
The generated Target Bands section lower on this page is the DB-backed control view. The notes here describe lettuce preferences; they should not be read as a second live setpoint schedule.
Varieties for This Greenhouse
| Variety | Type | Days to Harvest | Heat Tolerance | Notes |
|---|---|---|---|---|
| Butterhead (Bibb) | Head | 50-60 | Moderate | Classic, tender leaves |
| Romaine | Head | 55-70 | Good | More heat-tolerant than butterhead |
| Red leaf | Loose-leaf | 45-55 | Good | Fast, cut-and-come-again possible |
| Green leaf | Loose-leaf | 45-55 | Good | Workhorse variety |
| Oakleaf | Loose-leaf | 45-50 | Best | Most bolt-resistant |
| Recommendation: Start with a mix of romaine and red/green leaf. Leaf types are fastest and most forgiving. Oakleaf for summer planting — best bolt resistance. |
Zone Recommendation
Primary: East Zone hydroponic system The east zone runs 5-9°F below the greenhouse average during peak heat. On a day when the south zone hits 100°F, the east zone is at 91°F. For lettuce, this difference is the line between a head of lettuce and a flower stalk.
| Factor | East Zone Value | Lettuce Tolerance |
|---|---|---|
| Peak temp (hot day) | ~91°F | Bolts > 80°F sustained |
| Tree shade | Blocks morning direct solar | Reduces heat stress |
| Patio door ventilation | Additional cooling in summer | Helps but introduces dry air |
| Hydro humidity | Evaporation adds local RH | Improves VPD for lettuce |
| Seasonal viability: |
| Season | Viability | Notes |
|---|---|---|
| March-May | Excellent | Prime spring lettuce window; late May is the transition into heat management. |
| June-July | Marginal | Even east zone will be hot. Bolt-resistant varieties only. |
| August | Marginal | Monsoon moisture helps but heat is still a constraint. |
| September-October | Good | Fall crop window. |
| November-February | Good | Grow lights essential; heat cost offset by value. |
Hydroponic Growing Notes
- Media: Grodan rockwool cubes to net cups to clay pellets.
- Spacing: Every other position (positions 1, 3, 5…) gives 6” spacing for heads
- Nutrient formula: General Hydroponics Flora series, light concentration (EC 0.8-1.2)
- Days to harvest: 45-60 from transplant to hydro (add 10-14 for seedling stage)
- Harvest method: Cut at base for head types. Cut outer leaves for leaf types (extends to 2-3 harvests)
Succession Planting
For continuous harvest, stagger plantings by 2 weeks:
| Week | Action | Positions |
|---|---|---|
| 0 | Seed starts (Jiffy mix, east shelf heat mat) | Tray |
| 2 | Transplant batch 1 to hydro | HYDRO-1 through HYDRO-10 |
| 4 | Transplant batch 2 to hydro, seed batch 3 | HYDRO-11 through HYDRO-20 |
| 6 | Harvest batch 1, transplant batch 3 | Rotate positions |
| At 10 positions per batch with 2-week stagger, this yields continuous lettuce with 30 hydro positions dedicated. |
Longmont-Specific Notes
- Altitude effect: Higher-elevation UV can stress lettuce. The opal polycarbonate blocks 99% of UV — this is actually an advantage.
- Dry air: Outdoor RH of 14-18% in spring means the greenhouse VPD will push high. Climate Control explains the misting and VPD tradeoff.
- Water quality: Longmont municipal water is soft, low in dissolved minerals. Good for hydro — nutrient solution won’t need pH adjustment from high alkalinity.
See All Crops.
Catalog Entry
Slug lettuce; category leafy_green.
Cycle 45-60; scientific name —.
Default DLI; default VPD 0.60-1.00 kPa.
Crop-Control Status
Counts as active control. Occupied east-zone record in v_position_current; heat-sensitive crop context participates in active policy. Target Bands below show current DB-backed profile coverage.
Current occupied positions from v_position_current: none.
Target Bands
59.5–71.6°F; 0.49–0.93 kPa; DLI 14.0. Hours covered: 24.
59.5–71.6°F; 0.49–0.93 kPa; DLI 14.0. Hours covered: 24.
Current Plantings
No active Lettuce plantings are recorded right now.
Latest Vision
2026-06-07 06:00greenhouse_2 · east · health 8/10Lettuce: Seedlings appear healthy and are establishing well.
2026-06-07 02:00greenhouse_2 · east · health 8/10Lettuce: Seedlings appear healthy with no visible signs of stress.
2026-06-06 22:00greenhouse_2 · east · health 7/10Lettuce: Seedlings in hydroponic system appear generally healthy, though some are small.
Planting History
EAST-SHELF-T12026-03-01 to 2026-06-11102 days; final stage seedling; events 3.