Light potting compost with perlite for seedlings and cuttings

For the first few weeks, clean water is enough, because the light fertilisation in the mix supports the plant as it settles in. After that, the plant needs a fertiliser at almost every watering: Bio-Grow, from 2 ml per litre at the start up to 4 ml, is suitable during the leafy phase, and Bio-Bloom is then added for tomatoes or peppers that are flowering. For cuttings, Root-Juice at 4 ml per litre supports rooting during the first few weeks. Water gently, until the water soaks through the whole root ball without pooling on the surface. To fine-tune the solution, a liquid pH test kit tells you whether the irrigation water stays in the right range, around 6 to 7 for most vegetables.

In a pot or tray watered automatically, by drip irrigation or by wick, check that the water really does penetrate the compost. Very dry peat repels water at first, so it runs down the side of the pot without moistening the centre of the root ball; conversely, a grow medium that stays waterlogged encourages mould. So moisten the compost before potting on, working it with a little water until it holds together in a clump without dripping. For indoor seedlings, light and warmth matter as much as the compost, as explained in the article on the indoor seedling area.

The grow bed of an aquaponic system needs a inert, dust-free, pH-neutral medium that does not alter the quality of the fish water. A peat-based compost does not meet these criteria, and even coconut fibre, which is more stable, eventually breaks down and clogs the circuit. You therefore keep Light-Mix out of the system, for seedlings and for the pots in your vegetable garden, from herbs on the windowsill to tomato plants destined for the open ground. Its light fertilisation suits these young plants well, which stay in small pots while they form their roots.

Seedlings intended for the grow bed are better started in an inert medium, in a perforated grow pot filled with rock wool or coconut fibre, then join the system about two weeks after their first true leaves appear. If a seedling has nevertheless grown in the Light-Mix, gently wash its roots in lukewarm water before placing it in the grow bed, so that the peat ends up neither in the pond nor in the pump. The article which grow medium to choose in aquaponics compares the media suited to the circuit.