Hydroponic gutter system, 10 or 20 plants

Your 10 or 20 sites, over 2 or 4 linear metres, are best suited to short-cycle, low-growing plants: lettuce, mesclun, spinach, basil, parsley, chives, mint and strawberries. Solanaceous crops are possible but change the picture: a tomato or pepper plant takes up the aerial space of 2 to 3 salad plants and needs staking independent of the system; you then use only one site in two. Our guide what to plant in hydroponics, season by season details the cycles. One point worth making to spare you disappointment: the system takes plants that already have roots, not bare seeds. So allow for a seedling area upstream, however simple. In practice, staggered successions make the best use of the sites: a harvested plant frees up a place that you fill straight away with a young plant held in reserve, rather than emptying and restarting everything at once.

In a closed circuit with no buffering medium, the pH changes quickly, as your plants take up ions unevenly while evaporation concentrates the solution. The working range is 5.8 to 6.2, and a reliable means of measurement is part of the basic equipment. Our article on pH regulation applies here too, with one caveat: with no fish to look after, the correction can be bold rather than gradual. The solution is replaced entirely every 2 to 3 weeks depending on the plant load. In the 45 L tank, a correction spreads through in about twenty minutes, as the circulation constantly mixes the water; allow twice as long for the 150 L. Conductivity should be monitored alongside, since a level that falls while conductivity rises indicates that the plants are absorbing proportionally more water than nutrients, a gap that topping up with clean water corrects better than adding fertiliser. The temperature of the solution matters just as much, as dissolved oxygen becomes scarcer above 22 °C, precisely when root respiration intensifies.

You assemble the system dry, following the instructions, then comes a first fill with clean water: you run the pump for an hour to check that there are no leaks and that every channel flows in the same way. This is also the moment to check that they are level, and that the level tube of each one does return the surplus to the tank. You then prepare the nutrient solution and adjust the pH before installing anything. During the first week, check the tank level, the pH and the appearance of the roots every day, as these three daily readings reveal within a few days an assembly fault that a weekly check would miss.

Allow about 3 L of clay pebbles for 10 baskets of 8 cm, 6 L for 20, rinsed until the water runs clear, because clay dust is what clogs irrigation lines fastest. The 8 to 20 mm grade is suitable, and these pebbles can be reused from one crop to the next after a simple rinse. Your plants go in already rooted, whether a cutting that has taken or a shop-bought plant; a propagator or a simple seedling area will supply them. A plant in a peat plug should be rinsed before going into the basket, as the organic matter it releases would otherwise feed the biofilm in the channels. A plant started on a neoprene disc is also fine, provided the root tangle already protrudes from the bottom, otherwise the plant will not find the flow in the first few days.

The 10-plant occupies 117 x 50 cm of floor space, and the 20-plant 112 x 97 cm, with the tank sitting beneath the head of the channels. These are laid level, the level tube on each one setting the height of the water film and returning the surplus to the tank. The floor you choose must be flat and able to withstand water, as the 150 L tank alone weighs 150 kg when full. Finally, allow access on at least one side so that you can open the lid, measure and top up, otherwise every weekly check will force you to move the whole unit. Height is also worth anticipating, as the channels rest on the tank and the foliage grows above them, which easily brings the whole unit to 1.2 m under a suspended light.

Use the brush supplied between two crops: the channels are cleaned with clean water, then rinsed thoroughly, as the white plastic does not tolerate detergents, which leave a film. The pump strainer is rinsed each time the solution is changed, and the distribution line is checked at the same time, since a channel that drains more slowly than the others points to a deposit in its fitting. Once a season, circulate diluted white vinegar if your water is hard, then rinse twice before making up a fresh nutrient solution, as limescale reduces the pump's flow well before it becomes visible on the walls. Finally, check the seals on the channel end caps, as a slight seep ends up emptying the tank faster than evaporation does. A level reading noted down each week makes this kind of leak obvious, since consumption that doubles without the plants having grown points to a leak rather than to what the plants need.