Hydroponic NFT system for 36 plants, 80 mm channels

A spacing of 200 mm gives each plant room to spread without touching its neighbour, which matches the roughly twenty-centimetre spacing recommended for leafy vegetables grown to full size. Your heading lettuces therefore reach their mature size here, whereas a tighter spacing forces you to cut them young. Remove strawberry runners as soon as they appear, since they cannot root in a channel and they divert a share of the plant's reserves.

The 64-litre reservoir, measuring 60 x 40 x 32 cm, holds almost the entire volume of the circuit, as the channels retain only a thin film. The submersible pump, a Hailea HR1000 with a rated flow of 1,050 L/h, feeds the four channels through a four-outlet manifold, and the water returns to the reservoir via drainage plugs and 32 mm push-fit fittings. The plugs are factory-bonded to both ends of each channel, so all you need to do is connect the inlet and return lines.

In summer, the benefit is most noticeable in the afternoon, when the air inside a greenhouse or conservatory heats up faster than the solution protected by the air gap. The reservoir itself has no double wall: place it in the shade, out of direct sunlight, as it holds almost all the water in the system and sets the starting temperature. A thermometer left in the reservoir at the end of the day will tell you whether you are staying below the 20 °C threshold, or whether more shading is needed.

You dose the 64-litre reservoir by multiplying the per-litre rate. During full growth, TriPart is added at 1.8 ml of Grow, 1.2 ml of Micro and 0.6 ml of Bloom per litre, which is approximately 115 ml, 77 ml and 38 ml for a full tank, with an electrical conductivity of 1.3 to 1.8 mS/cm. When the strawberry plants are flowering, the ratio reverses: 0.8 ml of Grow, 1.6 ml of Micro and 2.4 ml of Bloom per litre, giving approximately 51, 102 and 154 ml, for an electrical conductivity of 1.4 to 2.2 mS/cm. Add each bottle separately, stirring between additions.

pH is adjusted last, once the three parts have dissolved, and should be checked weekly in the reservoir. If your system combines strawberries and herbs, stick to a single solution suited to the dominant crop rather than trying to find a compromise between very different requirements. Every 2 to 3 weeks, empty the reservoir and start fresh with a new solution, because the salts that plants do not take up accumulate over time. Between renewals, top up with plain water to compensate for evaporation. With strawberries, a pH that has remained too high for several days shows first on young leaves, which pale between veins that stay green, a sign that iron has become less available.

The frame is assembled from 23 mm square PVC and aluminium tubes joined by push-fit fittings, then receives the four channels. Allow two people for assembly, as a 1.85 m channel is awkward to position single-handed and a profile resting on a single support will twist. The standard reference for nutrient film technique is a slope of approximately 1 cm per metre, giving close to 2 cm of drop between the two ends of a channel: check this with a spirit level before filling with water.

Next, run a trial with plain water and the pump running, and check the flow at the end of each channel before installing a single plant. A channel that does not flow along its full length can be corrected in a few minutes while it is still empty. If your surface is not level, adjust the feet of the structure before filling the reservoir rather than after, since 64 litres of water makes every subsequent adjustment considerably harder.

Feeding your channels with water from a fish tank is perfectly viable, subject to two conditions. The first concerns pH, which must first suit the fish and nitrifying bacteria, around neutral, meaning you lose the freedom to lower it for the plants; the comparison between aquaponics and hydroponics covers this trade-off in detail. The second concerns suspended solids, which require mechanical filtration upstream; without it, they will settle on the bottom of the channels.

With this profile, the 80 mm height leaves more clearance than a low-profile channel before any sediment build-up obstructs the flow of the film. This clearance is no substitute for a filter, it simply extends the interval between cleanings. Keep the same maintenance habits as you would with a purely mineral setup, and check the water coming out at the end of the channels every time you walk past. If the flow drops on a single channel, the first thing to clear is the outlet of its feed line.

You receive the four double-walled channels with their removable lids and glued end caps, the supporting frame, the 64-litre reservoir, the pump and its supply line, the return circuit, and 36 net pots measuring 5 cm in diameter and 7 cm in height. Should a channel ever be damaged, replacement channels in the same profile can be ordered individually or in bulk.

The choice of pot filling depends on what you are planting. A bare-root strawberry plant sits directly in the pot, supported by clay pebbles larger than the slots, which hold the crown above the film without retaining water. A herb cutting or a lettuce seedling is better started in a germination sponge or a rockwool cube, which slots whole into the pot. In every case, the crown stays dry and only the roots reach the water film, which prevents rot at the base of the stem.