Hydroponic kit with 4 pots connected to a shared reservoir

As the four pots are connected to the reserve, you prepare a single solution, measure a single pH and fill a single reservoir. The float valve then maintains the shared level mechanically, reopening the inlet as soon as it drops. In return, the four plants receive the same solution, so they must be at the same stage and have the same needs. The controller acts here as the single measuring point, and it is its level tube that replaces the four readings that a set of independent pots would require.

Maintenance then comes down to three tasks a week. You read the level tube on the control pot, which shows the state of the whole network, and you top up the reservoir. You measure the pH at the same spot, since the five connected containers communicate and give the same sample, and you correct towards 5.8 to 6.2, letting the circulation mix for an hour before reading again. Every 2 to 3 weeks, you replace the entire solution rather than topping it up indefinitely: 120 litres becomes unbalanced just as surely as 15, only more slowly. This is the moment to rinse the strainers of the five columns and the float of the valve. A logbook, even a basic one, makes these readings far more useful, because the trend in pH over 3 weeks signals what a single measurement cannot. Water consumption is tracked in the same way: a gradual rise simply goes with the plants' growth, whereas a sudden drop calls for checking the condition of the roots before blaming the weather.

The choice of location comes before the first filling, as the full system weighs around 150 kg once the wet grow medium is counted. It needs a level floor that can bear the water, and enough clearance to walk around the four pots without moving anything. All five containers must sit at the same level, to the millimetre, because it is gravity alone that evens out the water heights between them. A slab, a load-bearing floor or a tiled surface will do; a board set on trestles, much less so. Once the pots are spaced out around the reservoir, also allow a walkway on at least one side. Finally, allow 10 litres of clay pebbles, grade 8 to 20 mm, per growing chamber, rinsed until the water runs clear, and four plants that are already rooted, all at the same stage.

Medium-sized plants grown together make the best use of these four 15 L pots, whether that means four basil plants, four chilli peppers, four strawberry plants or four lettuces. For tomatoes at full size, the 45 L reservoir shared between four empties quickly in summer: the 45 L pot used on its own is then more comfortable. Our guide to what to plant in hydroponics gives the cycles species by species. A good rule is to choose four varieties of the same species rather than four different species, so that the needs for light, nitrogen and staking height remain comparable from one pot to the next.

The bodies of this system are rotationally moulded in France from recycled polyethylene, and treated against light and ultraviolet rays. These bodies are guaranteed for life under normal use, and the air pump for 2 years. A wall that lets light through makes algae grow in the solution, and algae in a 120-litre network end up clogging all five pumping columns at once. The reservoir lid is solid and lifts at one side, which lets you fill and measure without dismantling anything, or exposing the solution to light for more than a few seconds. Rotational moulding also gives walls made in a single piece, with no weld or glued corner, in the places where an assembled tank eventually starts to seep. Polyethylene is cleaned with clean water and a sponge between two crops; it does not tolerate solvents and detergents, which leave a film on the walls. A whitish limescale deposit on the waterline comes off with diluted white vinegar.

The pump is the only active part of the kit, so its condition affects all four crops at once. Its diaphragms wear with the hours of continuous running: circulation then weakens in all five columns together, which sets it apart from a blocked strainer, which affects only one pot. Place it above the water level, otherwise a power cut will make the solution siphon back up the air line. A non-return valve fitted on the air line removes this risk. Finally, check that the distribution tees are not pinched behind a pot, as a crushed section is enough to starve a column of air without anything else changing.

The network is made up of just a few parts, and each can be replaced individually. The pots are connected to the reservoir by black tubes of 18 x 23 mm, two of 60 cm and three of 40 cm, distributed by five tees. On the controller side, two 16 mm barbed connectors and a 90° elbow join the 15 x 17.5 mm tubes. Each pot keeps its own distribution ring, pump column and strainer, the same as on the 15 L pot sold separately. If a fitting cracks, the 16 mm barbed connectors and elbows can be ordered in packs, without buying the kit again, and you can have the network back in service within the day.