NFT hydroponic system 60 plants, 2 m channels

Prepare the plants separately on an indoor seedling table, roughly 3 weeks ahead of transplanting. Several batches are therefore running at the same time: those germinating on the seedling table, and those occupying the four channels at different stages. Note the transplanting date for each channel on a label fixed to its end, that is all you need to know which one to harvest the following week.

The profile measures 100 by 50 mm and the positions are spaced every 125 mm, giving the planting density suited to short-cycle leafy crops: cut lettuces, young-harvested batavias, lamb's lettuce, rocket, spinach, basil, parsley, and coriander. Their rootball stays light and their root system won't clog the channel before harvest. If you're aiming for a full-sized head lettuce, leave every other position empty, as it needs around twenty centimetres between plants.

Plants that bulk up over several months will eventually fill the full depth of the channel, and their root mass will then start to restrict flow rather than follow it. If your project involves a long-term crop, strawberries or herbs grown as bushes, it is an 80 mm deep channel, spaced at 200 mm, that you should be looking at. Tomatoes and peppers, meanwhile, require a proper volume of water per plant, which only a deep water culture system can provide.

The 64-litre reservoir is dosed by multiplying the per-litre rate by the volume. At the appearance of the first true leaves, each of the three parts of TriPart is added at 1 ml per litre, giving 64 ml of each. At full growth, TriPart is dosed at 1.8 ml of Grow, 1.2 ml of Micro and 0.6 ml of Bloom per litre, which equates to approximately 115 ml, 77 ml and 38 ml for a full reservoir, with a conductivity of 1.3 to 1.8 mS/cm. Conductivity reflects the quantity of dissolved salts and tells you whether the solution is keeping up with plant uptake. For lettuce, adjust the pH to between 5.6 and 6.0 once all three parts have dissolved.

When all 60 positions are occupied, the solution is depleted much more quickly than with a single planted channel, and it becomes unbalanced proportionally sooner. Use conductivity as your guide rather than the calendar: if it rises without you having added anything, the plants are drawing water faster than salts, and topping up with clean water corrects the imbalance. Replace the entire solution every 2 to 3 weeks, and more frequently when all four channels are full of mature plants.

Tank water from a fish system can feed these channels, provided it first passes through mechanical filtration: a film just a few millimetres thick blocks quickly, and 60 positions multiply the spots where deposits can build up. You also give up the option of freely lowering the pH, since the range that suits fish and nitrifying bacteria, around neutral, takes priority over that of the plants.

The benefit lies in the growing surface: the more plants there are, the more nitrogen they take up, and 60 growing positions help to balance a pond where the fish produce a high output. This nitrogen comes from the breakdown of fish waste by bacteria, as described in the nitrogen cycle. The pond volume then acts as a buffer, and both pH and temperature fluctuate far more slowly there than in a 64-litre tank.

Check the pH and conductivity in the reservoir, top up the level, adjust the nutrient solution, and verify that water flows freely from all four channels. The standard reference in nutrient film technique is a slope of approximately 1 cm per metre, meaning a 2 cm drop between the two ends of a 2 m channel. A spirit level placed on each empty channel is sufficient to check this after moving or cleaning the system. While you're at it, rinse the pump strainer, since a partially blocked filter reduces the flow across all four outlets well before the film appears abnormal.

Twice a year, when a channel is empty, remove its cover and brush the interior along its full length. On a two-metre run, this is also a good opportunity to check that the profile has not sagged in the middle: a dip of just a few millimetres is enough to hold a puddle, and that standing water will turn green. If you find one, a support placed under the lowest point resolves the issue; if the flow remains uneven, replacement channels in the same profile can be ordered individually.

You receive the four 2 m channels with their removable covers drilled with 15 planting sites and their factory-glued end caps, the support frame in 23 mm square-section tubing, the 64-litre reservoir, the Hailea HR1000 pump with a rated flow of 1,050 L/h complete with its supply line, the return circuit, and 60 net pots of 5 cm. The covers lift off by hand, giving access to the full length of the channel for cleaning.