Nutrient Film Technique (NFT) — How It Works

Quick answer

Nutrient Film Technique (NFT) runs a continuous 1–3 mm film of nutrient solution down a gently sloped channel (1:30 to 1:40) at 1–2 L/min, with bare roots resting in the channel. It's the dominant commercial system for lettuce, herbs, and baby greens — but it's entirely pump-dependent and offers no buffer against power failure [CORN-CEA-01].

Parameters

How it works

A submerged pump circulates nutrient solution from a reservoir to the top end of each sloped channel. Solution flows down the channel as a thin film, washing past bare roots that have grown out of net cups, then drains back to the reservoir from the bottom end. The system runs continuously.

The "film" depth is critical: roots need access to both nutrient solution and air. A 1–3 mm film keeps the lower root surface wet while the upper root mass sits exposed to air, achieving the high root-zone oxygen levels that drive fast leafy-greens growth [CORN-CEA-01].

NFT vs Kratky

The two systems are opposites of the same axis:

• NFT: moving thin film, continuous oxygen via airflow, pump-dependent, scales to commercial.
• Kratky: static deep reservoir, oxygen via air gap as level drops, no pump, doesn't scale [KRATKY-ORIG].

NFT delivers consistently higher yields per square meter at the cost of complexity and power dependence. Kratky delivers near-zero ongoing labor at the cost of crop selection and scale.

Channel design

Standard channel dimensions in commercial NFT:

• Width 8–10 cm internal
• Depth 5–7 cm
• Length 6–12 m maximum (longer runs accumulate EC drift toward the end)
• Lid with planting holes at 15–25 cm spacing depending on crop

Slope below 1:50 causes pooling and anaerobic root zones. Slope above 1:25 strips nutrients past the root surface too quickly and reduces uptake [GROWER-LOGS].

Best crops

NFT excels at fast leafy crops with shallow root systems:

• Lettuce (all types)
• Arugula, bok choy, baby kale
• Basil, parsley, cilantro, mint
• Spinach (with cool water)
• Strawberry (specialized elevated NFT)

NFT fails for fruiting crops, root vegetables, and any plant with a heavy root mass. Tomato, pepper, cucumber, and most large brassicas block the channel within 6–10 weeks [CORN-CEA-01].

Failure modes

• Pump failure. The dominant failure mode. Plants wilt within 30–60 minutes under lights. Install a backup pump or UPS for any commercial install.
• Channel pooling from sediment. Algae, root debris, or particulate from organic additives. Flush channels every 4 weeks.
• EC stratification. Long channels accumulate EC drift — the last plant in a 12 m channel can see EC 0.5–1.0 higher than the first. Limit channel length or split feed lines.
• Algae growth. Light exposure to nutrient solution. Use opaque lids and dark channels.
• Crop-specific failures. Trying to grow tomato or pepper in NFT. Don't.

Power and water budget

A typical 50 m² NFT bench (roughly 200 channels of 6 m each) runs on a single 50–80 W circulation pump. Water consumption depends almost entirely on crop transpiration, not on the system — NFT itself loses almost no water to evaporation given the small exposed surface.

Reservoir sizing: 5–10 L per plant for full-cycle production, replenished every 14 days with fresh solution to prevent micronutrient drift [OSU-NUT-01].

What we recommend

For commercial leafy production at 10 m² and above, NFT is the right choice — cleaner harvest, easier sanitation between crops, and the highest plants-per-square-meter density. For hobby growers running fewer than 30 plants, the pump dependence rarely justifies the complexity over DWC. And under no circumstances should NFT be your only system if you can't tolerate a 30-minute pump outage without losing the crop — keep a backup pump, a backup power source, or run a hybrid with DWC buffer reservoirs.