The first year from seed

The seedlings are up and the box is still shut. From here almost everything you do is one small step in a long ramp — more light, less humidity, more room — and the whole skill is running it slowly enough. Get it right and you end up with fat little columns that hold themselves upright. Get it wrong and they stall, and a stalled seedling can sit there doing nothing for weeks.

Start when they have about three rows of spines, which is roughly two months in. Take the lid off for growing intervals over a week or two — five minutes, ten, fifteen, half an hour, an hour, then longer — until it can stay off. With cling film instead: a couple of pinholes, enlarge them a few days later, then nearly off, misting whenever the condensation stops coming back.

Push the light up about 10% at a time from a month after germination — what Germination means — one notch on a dimmer, an inch closer, half an hour longer — then leave them ten days to a fortnight to settle before the next step. Aim for roughly 500 PPFD — what PPFD means once they stand a couple of inches high, 750 across the whole tray somewhere in month six to eight, and 1,000 to 1,250 once they are past a year old. Driving light up as fast as they will take it is what produces fat seedlings that hold themselves upright and never need staking.

Water is where the seedling rules invert the adult ones. Never let a seedling dry out completely. Water while the mix is still slightly damp underneath, alternating a bottom soak with a top mist so it neither dries out below nor goes hydrophobic. Chlorine leaves water that has stood a few hours; chloramine, which is what most municipal supplies use now, does not — so use a dechlorinator, bottled spring water, or rain.

Feeding starts gently and arrives by about month five: alternate a liquid kelp product with a complete fertiliser plus calcium, magnesium and micronutrients, beginning at about half label strength. For scale — what Scale means, a first feed for a baby seedling sits around 0.7 mS/cm, a normal label-rate application around 1.8, and 3.5 is close to toxic.

Adults are about 3 mm and look like tiny mosquitoes. The larvae are about 6 mm, transparent, and live in the top layer of the mix. Only the larvae do damage, and only to seedlings between a few weeks and a couple of months old — a grown cactus is unaffected. The symptom is unmistakable: seedlings lying flat because their roots have been eaten.

Yellow sticky traps deal with the adults. For the larvae, weakest to strongest: raw potato slices laid on the surface and binned daily, then BTI — sold as mosquito dunks or bits — in every watering for two to three weeks, then predatory nematodes. BTI is the usual answer, and it spares the beneficial microbes.

Every seedling in the tray is a new individual, and it is worth sitting with that before you get attached to any of them. Two siblings out of one fruit differ in form, in vigour, and later in the size and shape of their flowers.

Which is the argument against culling. Do not throw out a plain-looking seedling early. It has not shown you what it is yet, and several of the things worth having only turn up later.