The first year from seed
One long ramp: more light, less humidity, more room. Change one thing at a time, in order. And none of them will look like either parent.
30-second version first, the whole guide below5 min read
The short version
- Rushed, they stall, growers say, and a stalled seedling can sit doing nothing for weeks.
- Punch small drainage holes at the lowest points the moment the top comes off, growers advise.
- Once fully uncovered: mist three times a day for a few days, then twice, then once, then every other day, growers say.
- Change one thing at a time. Light, humidity, temperature: stresses stack, growers say, and a seedling under two at once stops growing.
- Up-pot when they start touching each other. Competition slows them, and tangled roots get worse the longer you wait.
Your setup
Pick yours to see what changes in this guide.
Where it grows
In the ground
Seed-grown plants stay in pots a few years before going in the ground, growers say; planted out too young they stall.
In a pot
Plastic cells or small plastic pots, around 2.5 by 2.5 by 3 inches, growers say.
Keep the soil line high for airflow, and never sink a seedling down into the pot, growers advise.
Where it lives
Outdoors
Outdoors: four or five layers of 30 to 40% shade cloth, one off every couple of weeks, growers say; in a high-UV summer one layer may stay until fall.
Indoors
Even a strong indoor light is far weaker than summer sun, so seedlings raised under one still need the shade cloth, growers say.
The season
Winter
Nothing in this guide changes in winter.
Not winter
Nothing in this guide changes outside winter.
Lines are from this guide, or from the cultivar library where one says so. For where they come from, see the end of the guide.
Introduction
The seedlings are up and the box is still shut. Everything from here is a slow ramp, growers say: more light, less humidity, more room. Going slowly keeps seedlings growing. Done right, growers say, you get fat little columns that hold themselves upright. Rushed, they stall, growers say, and a stalled seedling can sit doing nothing for weeks.
Opening the box
Start at about three rows of spines, roughly two months in. Over a week or two, take the lid off for longer each time: five minutes, ten, fifteen, half an hour, an hour, until it stays off. If you used cling film instead, put in a couple of pinholes, enlarge them a few days later, then pull it nearly off, growers say. Mist whenever the condensation stops coming back.
Weeks one to two
a ball and two cotyledons
Month three
areoles · first bristles
Year one
ribs · proper spines
- Punch small drainage holes at the lowest points the moment the top comes off, growers advise. A hot metal skewer makes a clean hole.
- Remove the heat mat at the same time. From here on it only dries the mix.
- Once fully uncovered: mist three times a day for a few days, then twice, then once, then every other day, growers say.
- Run a fan across them from day one uncovered.
- Change one thing at a time. Light, humidity, temperature: stresses stack, growers say, and a under two at once stops growing.
Sealed, and left alone
condensation on the walls
About two months — it comes off
three rows of spines · holes punched
Light, water and food
From a month after , raise the light about 10% at a time (one notch on a dimmer, an inch closer, half an hour longer), growers say, then leave them ten days to two weeks before the next step. Seedlings pushed to the limit of what they can take bleach and stall, growers say; steady, staged increases are what make them sturdy.
- About 500 at a couple of inches tall.
- 750 across the whole tray in months six to eight.
- 1,000 to 1,250 past a year old.
Watering flips the adult rule. Never let a seedling dry out completely. Water while the mix is still slightly damp underneath, growers advise, and alternate a bottom soak with a top mist so it neither dries below nor goes hydrophobic. Chlorine leaves standing water in a few hours; chloramine, in most municipal supplies now, growers say, does not. Use a dechlorinator, bottled spring water, or rain.
Feeding starts gently, growers say, by about month five: use a complete fertilizer with calcium, magnesium and micronutrients, at about half label strength to begin. For scale, growers say, on an meter in mS/cm: a baby seedling's first feed is around 0.7, a normal label-rate feed 1.8, and 3.5 is close to toxic.
Moving them on
- Up-pot when they start touching each other. Competition slows them, and tangled roots get worse the longer you wait.
- At about six months, or 2 to 3 inches tall, separate them. Do it under running water if the roots have knitted.
- Seedling mix differs from adult mix in exactly two ways: grit down to an eighth to a quarter inch, and a bit more matter, since a small plant carries less water, growers say.
- Plastic cells or small plastic pots, around 2.5 by 2.5 by 3 inches, growers say. Not terracotta or fabric. Both dry a small soil volume far too fast.
- Keep the soil line high for airflow, and never sink a seedling down into the pot, growers advise.
- Outdoors: four or five layers of 30 to 40% shade cloth, one off every couple of weeks, growers say; in a high-UV summer one layer may stay until fall. Even a strong indoor light is far weaker than summer sun, so seedlings raised under one still need the shade cloth, growers say.
- Seed-grown plants stay in pots a few years before going in the ground, growers say; planted out too young they stall. can go straight in.
Touching each other
competing · roots knitting
Separated
one cell each · soil line high
Fungus gnats: the one pest that matters
Adults: about 3 mm, like tiny mosquitoes. Larvae: about 6 mm, transparent, living in the top layer of the mix. Only the larvae do damage, growers say, and only to seedlings a few weeks to a couple of months old — a grown cactus is unaffected. The sign: seedlings lying flat, roots eaten.
Yellow sticky traps deal with the adults. For the larvae, weakest to strongest:
- Raw potato slices on the surface, binned daily.
- Growers use BTI (sold as mosquito dunks or bits) in every watering for two to three weeks. The usual answer, and it spares the beneficial microbes.
- Predatory nematodes.
The adult
about 3 mm · like a tiny mosquito
The larva
about 6 mm · clear body · dark head
None of them will be the parents
Every seedling is a new individual. Siblings from one fruit differ in form, in vigor, and later in flower size and shape.
- A parent that passes the trait on can, growers say, throw dozens to hundreds of monstrose seedlings from one fruit. One recorded case did exactly that. A different line gave three multi-headed out of sixty.
- Some crosses reliably throw variegation, one grower reports: five variegated out of thirteen in one pot from a terscheckii . Variegated seedlings grow noticeably slower while establishing.
- A split-headed seedling promises nothing. Several have grown up entirely ordinary.
- A normal-looking plant can carry monstrose genes without ever showing them, growers say. One grower says they only found out when about half its seedlings came out monstrose.
One clone, cut up
three pieces · one plant
One fruit, sown
three seedlings · three plants
So do not throw out a plain-looking seedling early. It has not shown what it is yet, growers advise, and several of the things worth having only turn up later.
Common mistakes, try it, quick check and sources
Quick check
Question 1: When do you start opening the container?
Question 2: Adult cacti get watered by letting them dry right out. Do seedlings?
Question 3: Your seedlings are lying flat and their roots are gone. What did it?
