An NFT system is unforgiving of planning mistakes because almost everything is fixed once the channels are mounted. This lesson works through the decisions in the order they constrain each other.
1. Siting: what the location has to provide
Before choosing a system, confirm the intended spot can supply all five of these. If any one is missing, pick a different spot.
- Light — six or more hours of direct sun for outdoor systems, or space and power for grow lights indoors. Leafy crops are the least demanding, but they still need real light.
- A power point — within reach of the pump cable, on an RCD-protected circuit. Water and electricity share this space permanently; this is not the place for an extension lead running across a wet floor.
- A level, load-bearing surface or wall. Water weighs 1 kg per litre, so a 100 litre reservoir is 100 kg before you add wet channels and plants — a wall-mounted system needs fixings rated for it and, ideally, masonry rather than plasterboard.
- Drainage or tolerance for spills. You will spill. Commissioning, reservoir changes and the occasional blocked channel all put water on the floor.
- Shelter from wind. Vertical systems present a large sail area and hold top-heavy plants in shallow pots.
Temperature is the constraint people miss
The target for the solution is 18 – 22 °C. Above roughly 24 °C, two things happen at once: dissolved oxygen falls, and Pythium — the organism behind root rot — becomes far more aggressive. A dark reservoir standing in full afternoon sun will exceed that comfortably in a Cape Town summer.
Site the reservoir in shade, insulate it, or both. This is much cheaper than treating root rot later.
2. Sizing the reservoir
Size the reservoir by plant count, not by what fits under the bench:
- 1.5 – 2 litres per plant site — a sound working minimum for leafy crops, and where most compact systems land
- 3 – 4 litres per plant site — comfortable, with real margin for error
Reservoir volume buys you stability. In a small tank, every litre the plants drink measurably concentrates what remains, so EC climbs and pH swings between top-ups. In a large tank the same uptake barely moves the numbers. Undersizing is the single most common cause of "my pH will not stay put".
Running at the lean end is perfectly workable — it just means the routine is not optional. Check pH and EC every two to three days rather than weekly, keep the tank topped up (a half-empty reservoir drifts twice as fast), and change the solution completely every one to two weeks.
Two practical points:
- Working volume is not tank volume. Leave headroom, and keep the pump inlet submerged at all times. A tank sold as 100 litres might hold 85 litres of usable solution.
- Use an opaque tank. Light reaching the solution grows algae, which consumes nutrients, fouls the pump inlet and crashes dissolved oxygen overnight.
3. Sizing the pump
Two numbers matter, and the second is the one people forget.
Flow rate. Aim for 1 – 2 litres per minute reaching each channel. Below about 1 L/min the film breaks into rivulets and parts of the root mat dry out; above about 2 L/min the film deepens and starts to drown the mat. A tap on the feed line lets you trim this — always fit one.
Head height. A pump's quoted flow is its flow at zero lift. Pushing water to the top of a 1.6 m vertical system costs you a large fraction of that. Read the pump's head curve, not its headline figure, and add the vertical rise from the water surface in the tank to the highest channel inlet, plus a margin for friction in the pipe and fittings.
A pump rated "1500 L/h" may deliver less than half that at 1.6 m of head. If your top channel runs dry while the bottom one floods, insufficient head is the first thing to check.
On air pumps: an air pump and air stone in the reservoir are not strictly required for NFT — the root mat already breathes air in the channel. They are still worth adding. Aeration keeps dissolved oxygen high in the tank itself, discourages anaerobic pockets and stagnation, and gives you margin on warm days.
4. Channel slope and run length
Slope should be 1:30 to 1:40 (roughly 25 – 35 mm of fall per metre). Too flat and the solution pools, deepens and stagnates. Too steep and it races through without wetting the full root mat.
Keep individual channel runs under about 10 metres. Beyond that the solution arrives at the far end measurably depleted in oxygen and nutrients, and the plants at that end visibly lag. For a home or small commercial vertical system this is rarely a constraint, but it matters if you scale out horizontally.
5. Plant spacing
Spacing is set by the pot holes, so it is fixed at build time. Get it right the first time.
| Crop | Spacing along channel | Notes |
|---|---|---|
| Lettuce (butterhead, cos) | 200 – 250 mm | The standard NFT crop |
| Loose-leaf lettuce, rocket | 150 – 200 mm | Cut-and-come-again tolerates tighter |
| Basil | 200 – 250 mm | Gets bushy; do not crowd |
| Coriander, parsley | 150 mm | Can be sown in clusters |
| Pak choi, chard | 250 mm | Wide leaf spread |
| Strawberries | 200 mm | Allow room for runners |
Crowding costs more than yield. A dense canopy holds humidity around the leaves, cuts airflow and invites downy mildew and botrytis. It is genuinely better to run 20 well-spaced plants than 30 crowded ones.
6. Choosing your first crop
Grow lettuce first. It is fast — typically five to six weeks from transplant — forgiving of EC and pH wobbles, visibly communicative when unhappy, and the crop every NFT reference is written about. You will learn your system's behaviour on a short cycle and cheap seed.
Resist the urge to plant six different species in your first run. Different crops want different EC, and a single shared reservoir can only be at one EC. Mixing a light-feeding herb with a hungry brassica in run one means neither performs and you cannot tell why.
Planning checklist
- Site confirmed for light, power, load, drainage and shelter
- Reservoir shaded or insulated, opaque, 2 – 4 L per plant site
- Pump flow verified at working head, feed tap fitted
- Channel slope set to 1:30 to 1:40 (roughly 25 – 35 mm of fall per metre)
- Spacing matched to the intended crop
- Backup power for the pump decided (see Part 1)
- First crop chosen — one species
With the plan settled, Part 3 covers the build.
Basic Hydroponics Training — the full series
- Part 1 — NFT Hydroponics Explained: How the Nutrient Film Technique Works
- Part 2 — Planning Your NFT System: Space, Water, Power and Crop Choice (you are here)
- 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.