Hydroponic pack for 20 plants: system, grow medium and nutrients

Doses are given per litre of solution, to be multiplied by the volume you are preparing. In full growth and in hydroponics, allow 1.8 ml of Grow, 1.2 ml of Micro and 0.6 ml of Bloom per litre. In flowering, the ratio reverses, with Bloom rising to 2.4 ml and Micro to 1.6 ml. Aim for a conductivity of 1.3 to 1.8 mS in full growth, and a pH of 5.5 to 6.5. Adjust the pH last, once all three parts have been added, because each one changes the value. In 150 litres, a correction takes about forty minutes to spread through the solution despite the constant circulation, so take the check reading after that delay rather than straight after pouring. The article on pH regulation explains how to follow its trend over time.

The test supplied is colorimetric: a few drops of reagent go into a sample, then you compare the colour against the chart. The 60 ml bottle comfortably covers a season of frequent readings, and it needs no calibration, buffer solution or battery. Two conditions are necessary for the reading to be worth anything: daylight and a white background, because pink horticultural lighting makes the comparison impossible. In practice you read to the half point, not the tenth, which is more than enough to keep within a range. Always take the sample from the same spot in the reservoir and after stirring, since a sample taken just after an addition does not represent the whole reservoir. Store the bottle away from light, as colorimetric reagents lose accuracy once exposed to sunlight for long periods.

The pH-down supplied is 100% urea phosphate, a powder that is inert when dry and becomes acidic once dissolved. It dissolves at a rate of 1 g per 5 to 6 litres of water, and this correction solution is then added in small amounts, measuring after each addition, with the total quantity depending on the hardness of your water. This salt is made of urea and phosphoric acid, so it adds phosphorus and nitrogen to the solution at the same time as it lowers the pH. At a typical correction dose the contribution is marginal, but it explains why very hard water that needs a lot of corrector ends up more heavily loaded than expected. The 250 g supplied covers several complete refills of the tank on water of medium hardness. Store the powder dry and sealed, as it absorbs moisture from the air and eventually cakes into a lump that is hard to dose.

Assemble the system dry following the instructions, then fill with clean water and run it for an hour: you are checking watertightness and above all that the flow is equal across the four channels. Rinse the clay pebbles, fill the baskets, prepare the solution, adjust the pH, and transplant plants that are already rooted. After that, the solution is replaced completely every 2 to 3 weeks; between changes, you only make up for evaporation with clean water. If your plants are not ready, the article on the indoor seedling area describes the corner to set up 3 to 4 weeks beforehand. During the first week, a daily check of the level, the pH and the appearance of the roots reveals an assembly fault much sooner than a weekly check.

The 4 linear metres of gutter primarily host short, low-growing crops: lettuce, mesclun, spinach, basil, parsley, chives, mint and strawberries. Tomatoes and peppers also grow there, at a rate of one position in two, since a single plant produces as much foliage as 2 to 3 lettuces and needs staking on a structure separate from the system. To keep all 20 places filled, stagger your plantings: each harvest frees up a basket, which immediately receives a young plant prepared in advance. The guide to hydroponic crops through the seasons tells you what to plant in each season.

Between crops, scrub the four channels with clean water and the brush supplied, without detergent, because detergents leave a film on the plastic, then rinse them thoroughly. Each time you renew the solution, rinse the pump strainer and compare the flow in the four channels, as a channel receiving less indicates a deposit in its distribution fitting. The drain kit supplied saves you from bailing out 150 litres by hand: connect it during assembly, at an accessible spot. Also note the reservoir level each week, since a sudden drop with no change in the plants often points to a leaking cap seal. In hard water, a pass with diluted white vinegar once a season, followed by two rinses, dissolves limescale before it reduces the flow.