Nutrient Film Technique (NFT) is one of the most water-efficient ways to grow leafy crops, and one of the easiest to get wrong. This first lesson covers the principle. Get this right and the remaining five parts are mostly plumbing and routine.
The core idea: a film, not a flood
In an NFT system, a pump lifts nutrient solution from a reservoir to the high end of a sloped channel. The solution runs down the channel as a shallow film — typically 1 to 3 mm deep — passes under the plant roots, and drains back into the reservoir to be pumped around again. Nothing is discarded.
That shallow depth is the whole design. It is what separates NFT from deep water culture or flood-and-drain:
- The root mat sits half in, half out. The lower surface of the root mass sits in the flowing film and takes up water and nutrients. The upper surface sits in humid air inside the channel and takes up oxygen directly.
- Oxygen is never the limiting factor. Roots in a deep, still solution depend entirely on dissolved oxygen in the water. Roots in a 2 mm film breathe air. This is why NFT crops grow fast.
- Water use is very low. Because the solution recirculates and the channels are enclosed, evaporation is minimal. An NFT system typically uses a fraction of the water of the equivalent soil bed.
Make the film too deep and you drown the root mat — you have built a very inefficient deep water culture system. Make it too shallow or let it run intermittently and the mat dries and dies. The narrow window between those two failures is what you are managing.
What a complete NFT system contains
Every NFT system, from a three-tier wall unit to a commercial greenhouse bench, has the same six parts:
- Channels (or gutters) — the sloped enclosed profiles the film runs through. Usually 50 mm to 100 mm wide, with holes cut for net pots.
- A reservoir — the tank holding the working solution.
- A delivery pump — a submersible pump in the reservoir feeding the top of each channel.
- Feed plumbing — a riser and manifold splitting flow between channels, with a tap to trim the rate.
- A return path — piping that carries solution from the low end of the channels back to the reservoir by gravity.
- Net pots and media plugs — usually 50 mm net pots holding a rockwool or coco plug that supports the seedling until roots reach the film.
On a vertical system the channels are stacked on uprights and the return often cascades: the pump feeds only the top channel, whose outlet drops into the next channel down, and so on, with the bottom channel returning to the tank. One pump, several tiers, and gravity doing the rest.
A cascading vertical layout is elegant but has one consequence worth knowing now: the lowest tier receives solution that has already passed every tier above it. It will run slightly warmer, slightly more depleted, and slightly higher in EC. Plan to rotate crops between tiers, or put your least demanding crop at the bottom.
What NFT grows well — and what it does not
NFT suits fast, shallow-rooted, lightweight crops. It is the standard commercial method for salad leaf worldwide for good reason.
| Grows very well | Workable with care | Avoid in NFT |
|---|---|---|
| Lettuce (all types) | Strawberries | Tomatoes and peppers |
| Basil, mint, coriander, parsley | Pak choi and other brassicas | Root crops — carrots, beetroot, potatoes |
| Rocket, spinach, chard | Dwarf beans | Maize, squash, anything tall or heavy |
| Watercress, celery | Kale (needs wider spacing) | Anything needing a long, dry finish |
The exclusions come down to three things: weight (a fruiting tomato will tear itself out of a 50 mm net pot), root volume (a root crop has nowhere to swell in a 2 mm film), and root mat thickness (a vigorous long-season plant builds a mat thick enough to dam the channel and flood it).
The one weakness you must design around
NFT has almost no buffer. There is no reservoir of water at the root zone — only the film. If the pump stops, the film drains away within a minute or two and the root mat begins drying immediately. On a warm day, unprotected roots can be permanently damaged in under an hour, and a full crop can be lost in an afternoon.
For South African growers this is not a theoretical risk — it is a scheduled one. Any NFT system here needs a plan for power interruptions:
- Put the pump on backup power. A submersible pump of the size used in a small NFT system draws very little; a modest inverter or UPS will carry it through a typical outage window.
- Or run the pump on 12 V solar. A solar pump kit sidesteps grid dependence for the circulation loop entirely.
- Increase reservoir volume. A larger tank will not keep the film running, but it does slow temperature swings and nutrient drift, which buys you margin everywhere else.
- Know your outage schedule and avoid transplanting immediately before a long one — young plants with short roots have the least tolerance.
We return to this in Part 6, where a pump failure checklist is the first item.
Is NFT the right choice for you?
Choose NFT if you want fast turnover of leafy crops, low water use, and a clean harvest with no growing medium to dispose of. Choose something else if you want to grow fruiting crops, if you cannot guarantee near-continuous power to the pump, or if you want a system that tolerates being ignored for a week.
If that still sounds like the right fit, Part 2 covers planning: siting the system, sizing the reservoir and pump, and choosing what to grow first.
Basic Hydroponics Training — the full series
- Part 1 — NFT Hydroponics Explained: How the Nutrient Film Technique Works (you are here)
- Part 2 — Planning Your NFT System: Space, Water, Power and Crop Choice
- Part 3 — Assembling a Vertical NFT System: Channels, Slope and Plumbing
- Part 4 — Commissioning Your NFT System: First Fill, Nutrients, pH and EC
- Part 5 — Planting Out: From Seed to Channel
- Part 6 — Weekly Maintenance and Troubleshooting for NFT Systems
Own our wall-mounted system? Setting Up the Hydro Works Wall-Mounted NFT System gives you the build and commissioning steps for that specific unit.