Your growing medium decides what your daily routine as a grower will look like before you even sow your first seed: it sets how often you water, your margin for error on pH and how fast your plants grow. By the end of this step, you'll know how to choose between soil, coco and hydro based on the time you can commit, how to size your pots from starter cell to final pot, how to repot without stressing your plants and how to manage drainage without falling into the gravel-at-the-bottom trap.
Soil: the forgiving medium
Soil is a living medium, buffered and already loaded with nutrients. It holds water and nutrients, then releases them over the following days: a missed watering, a slightly heavy dose of fertiliser or an imperfect pH are all cushioned rather than paid for on the spot. It's the forgiving medium, and that's exactly why we recommend it for a first cycle.
The number that drives it: in the root zone, tomatoes want a pH of 6.2 to 6.8. That's the "buffered" promise made measurable: as long as you stay within that range, the plant takes up what it needs. A quality light-mix potting soil arrives calibrated right around there, with a pH of 6.2 to 6.4 in the bag, a gentle EC of 1.2 to 1.5 mS/cm and roughly 30 % perlite in its composition. Two families to know:
Light-mix
You steer the feeding yourself.
All-mix
Handy for several weeks, but less controllable, and capable of burning a young plant if you repot into it too early.
With a light-mix, once the plant has been moved into its permanent soil, you start feeding when it carries 2 to 4 true leaves, meaning roughly 10 to 15 cm tall, then 1 to 3 times a week rather than at every watering (rule of thumb), with water adjusted to between pH 6.2 and 6.5 (rule of thumb). At the seedling stage proper, in the propagator, the dose is lighter and more diluted: the details are in step 5. As for watering, the instinct is simple: you water when the medium starts to dry at the surface, which indoors, in a pot of around 10 L, works out to a watering every 3 to 4 days (rule of thumb). Two limits you must never cross: too much water kills in the end, because roots starved of oxygen suffocate; and soil that dries out completely makes flowers and fruit drop.
Field tip: be wary of very peaty soil left too dry. Dry peat shrinks, turns hydrophobic, and your watering just runs down the sides of the pot without ever wetting the heart of the root ball. The plant looks "overwatered" when it's actually dying of thirst. The fix: rehydrate slowly, in small repeated volumes or by soaking the pot from below, and always check the heart of the root ball, not just the surface.
🍅 Tomatoes are made for soil: it's in a light potting mix, one that breathes between waterings, that they express their full potential with the least management. And one rule with no exceptions: never garden soil in a pot. Too dense, loaded with weed seeds and pathogens, it smothers roots in a container.
