Lettuce (Lactuca sativa)

📚 Family/Class: Asteraceae (국화과) 🌱 Genus/Sub-category: Lactuca (상추속) 🧬 Species/Type: Lactuca sativa 🌍 Origin: Mediterranean & Eurasia

Lettuce is the primary crop for indoor vertical farming (VF) and nutrient film technique (NFT) greenhouses. Because it is harvested for its leaves, steering is focused entirely on maximizing vegetative biomass while preventing tip-burn (caused by localized calcium deficiency under low transpiration in stagnant air). Controlling DLI (Daily Light Integral) and root-zone oxygenation are critical success factors.

Global Climate Strategy

🌍 United States (Vertical Farm LED)

Grown in fully enclosed vertical stack environments under LED lighting. Target DLI is 14 - 17 mol/m²/day. Focus is on localized air speed (0.3 - 0.5 m/s) using vertical fans to break the boundary layer of the inner leaves, preventing tip-burn.

⚙️ Tech Level: Very High (Fully closed HVAC, multi-tier LED racks, vertical air circulation)

🌍 South Korea (NFT Greenhouse)

Cultivated in hydroponic NFT (Nutrient Film Technique) gutters. Relies on shading screens and evaporative cooling pads to keep root-zone temperatures below 20°C in summer, preventing root rot and bolting. ^[1]

⚙️ Tech Level: Medium/High (NFT gutters, cooling pads, shading systems)

Crop Steering Parameters

Since lettuce is sold for vegetative mass, steering focuses on maximizing leaf growth speed without triggering bolting (flowering) or tip-burn.

Parameter	🌱 Vegetative Target (Leaf Growth)	🍅 Generative Target (Fruit Growth)
Temperature DIF	Low temperature DIF and cool ADT (Day 18-20°C / Night 14-16°C). Keeps plant in vegetative state.	High temperature DIF or hot ADT (above 24°C) triggers unwanted generative steering (bolting, bitter taste). Avoid.
VPD (kPa)	0.5 - 0.8 kPa (Ensures moderate transpiration without leaf stress).	VPD above 1.2 kPa causes excessive transpiration, leading to leaf margin drying and tip-burn. Avoid.
Irrigation & Space Strategy	Continuous flow (NFT) or high water frequency (Deep Water Culture) to prevent dry-backs.	Allowing root-zone dry-backs induces generative stress, causing bitterness and root damage. Avoid.

Fertigation Strategy

Lettuce has a very low salinity tolerance compared to fruiting crops. Keeping EC low and calcium availability high is vital.

Phase 1: Vegetative Vigor

Nitrogen-heavy formulation with high Nitrate-to-Ammonium ratio. Target EC: 1.2 - 1.6 mS/cm. Maintain dissolved oxygen (DO) above 6-8 ppm.

Phase 2: Generative / Brix Steering

Not applicable (avoid generative shift). Maintain vegetative EC throughout the entire growth cycle (seedling to harvest).

Ready to steer your crop?

AgriAtlas provides the theory, but every greenhouse is unique. Use our precise engineering calculators to hit these target VPD and Temperature DIF values based on your specific facility's U-Value and heating capacity.

Run VPD Calculator Calculate Heat Loss