# Nutrient film technique (NFT)

> In NFT a thin, continuous film of nutrient solution runs down sloped channels past bare roots. It is efficient and well proven for lettuce and herbs, but large cannabis root masses can dam the channel, and roots dry within one to three hours if the pump stops. Keep flow continuous (about 1–2 L/min per channel), slope about 1:30 to 1:100, and solution at 18–22 °C.

- Canonical: https://genetixbay.com/knowledge/systems/nft.html
- Category: Systems · Level: Advanced
- Evidence: Supported · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Flower · Systems: NFT
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**Does NFT work for cannabis?** NFT works for cannabis clones, [mothers](https://genetixbay.com/knowledge/glossary/mother-plant.md), short-veg [sea-of-green](https://genetixbay.com/knowledge/glossary/sog.md) and small plants, but it struggles with full-size flowering plants. Large cannabis root masses build mats that dam the channel, and roots can dry within 1–3 hours if flow stops. NFT is well established for lettuce and herbs, while NFT for big flowering cannabis remains grower practice with no published comparisons.

**What flow rate for an NFT channel?** An NFT channel for cannabis typically runs about 1–2 litres per minute of continuous flow, a starting default similar to leafy-green guidance that should be verified per system. The film should be only a few millimetres deep, since a deep, slow film causes [root rot](https://genetixbay.com/knowledge/glossary/root-rot.md). At lights-off you can reduce flow, but never stop it, and confirm return flow at every channel daily.

**What slope should NFT gullies have?** NFT gullies should slope about 1:30 to 1:100, which is a 1–3% fall, so solution runs as a thin film past the roots; check the figure against hydroponic reference texts. Keep channels no longer than about 10–15 metres, because long runs deplete oxygen and nutrients at the far end. Use wide, flat-bottomed, light-proof channels for cannabis.

**What happens if my NFT pump stops?** If an NFT pump stops, the thin film drains away and bare cannabis roots can dry out within 1–3 hours, so plants wilt within hours. NFT has almost no buffer, unlike media-based systems. Fit a flow alarm on the return, put a backup pump on the same manifold if you can, and confirm return flow at every channel daily or by sensor.

**Short answer.** A pump sends a **thin film** of solution down a gently sloped channel; roots sit in the film with their upper surface in air, so they get water and oxygen at once. It is a mature system for leafy greens [1][2]. For cannabis it works best for **clones, mothers, short-veg SOG and small plants**; big flowering plants build root mats that dam the channel, and the system has almost no buffer: roots can dry in **1–3 hours** without flow [4].

## Numbers that matter

| Parameter | Target | Notes |
|---|---|---|
| Flow per channel | 1–2 L/min | Jardin default |
| Slope | 1:30–1:100 (1–3 %) | |
| Channel length | ≤ 10–15 m | Long channels deplete O₂ and nutrients at the far end |
| Film depth | A few mm | Deep, slow film = root rot |
| Solution temperature | 18–22 °C (64–72 °F) | [3] |
| [pH](https://genetixbay.com/knowledge/glossary/ph.md) / [EC](https://genetixbay.com/knowledge/glossary/ec.md) | pH 5.6–6.0; EC as [DWC](https://genetixbay.com/knowledge/glossary/dwc.md) | |
| Lights-off | Reduce flow if desired, never stop | [4] |

## How to run it

1. Wide, flat-bottomed channels for cannabis; lids that block light.
2. Start plants in [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) or a small [net pot](https://genetixbay.com/knowledge/glossary/net-pot.md) so the root ball sits in the film.
3. Confirm return flow at every channel daily (or by sensor).
4. Prune or redistribute root mass if it starts to pond.
5. Backup pump on the same manifold if you can.

## Failure modes

| Problem | Sign | Jardin response [4] |
|---|---|---|
| Pump failure | No return flow, wilting within hours | Switch to backup pump; escalate alert |
| Channel blocked by roots | Water at the inlet end rises/overflows | Inlet high float → pump off, "channel blocked" |
| Film too deep/slow | Brown roots at outlet end | Flow and temperature trend |
| Warm solution | Root rot | [Chiller](https://genetixbay.com/knowledge/glossary/chiller.md), shade the channels |

## Jardin notes

Jardin method "NFT": flow meter on the return is the proof that a film exists; pump current; inlet-end high float; a 30 s loss of return flow with pump current = blockage or split; with zero current = pump dead. Automation level 3 [4].

## Safety

Water + electricity: GFCI/RCD, drip loops, leak trays under the reservoir.

## Common mistakes

- Using lettuce channels for big flowering plants.
- Narrow channels that dam within weeks.
- No flow alarm.

## Evidence

NFT for leafy crops is *Established* [1][2]. NFT for full-size flowering cannabis is *Grower practice* with no published comparisons we can cite.

## Sources

1. Cornell CEA. Hydroponic lettuce handbook. https://cea.cals.cornell.edu/
2. Resh HM, 2022. Hydroponic Food Production, 8th ed. CRC Press (NFT chapter). https://doi.org/10.1201/9781003133254
3. Colorado State University Extension PlantTalk 2043. Root disease problems and management in hydroponic systems. https://planttalk.colostate.edu/topics/miscellaneous/2043-root-disease-problems-management-hydroponic-systems/
4. GenetixBay Jardin engineering notes, 2026 (system profiles and failure margins).