How do I prick out seedlings without killing them?

Pricking out feels precarious and it is not. Seedlings are far more robust at the roots than they look and far more fragile at the stem than people assume. A crushed stem is fatal because the plant's entire plumbing runs through it; a torn seed leaf costs nothing, because the plant is about to discard them anyway.

What you'll need

• Modules or small pots
• Multipurpose or potting compost
• A dibber, pencil or plant label
• A tray to water from below (optional)
• Labels

Step by step

1. Wait for the first true leaves.The first pair to appear are the seed leaves — usually smooth, simple, and nothing like the adult leaf. The next pair are the true leaves and they are the signal. At the seed-leaf stage there is barely any root to lift.
2. Do not leave it much longer either.Once the seedlings in a tray have two or three sets of leaves, their roots have interlaced and every one you lift tears several others. A day early beats a week late.
3. Prepare the new pots first.Fill, level, tap down and water them before you start, so a lifted seedling goes straight into a ready hole rather than waiting on the bench drying out.
4. Water the seed tray an hour beforehand.Damp compost holds together around the roots. Bone-dry compost falls away and leaves the roots bare and exposed.
5. Work in the shade and out of the wind.Roots on a seedling can dry in less than a minute in sun or a breeze. This is the single largest avoidable loss.
6. Lever from underneath with a dibber.Push a dibber, a pencil or an old plant label into the compost beside the seedling and lift, so the root comes up with compost around it rather than being pulled out.
7. Hold a seed leaf, never the stem.Pinch one seed leaf between finger and thumb to steer it. The stem bruises at a pressure you will not notice applying, and a bruised stem collapses two days later.
8. Make a hole deep enough for straight roots.The root should hang down without curling or doubling back. If the hole is too shallow the root turns up at the bottom and the plant never establishes properly.
9. Set them deeper than they were.Lower the seedling until the seed leaves are just clear of the compost surface. Burying the bare stem produces a much stockier plant, and tomatoes, brassicas and most annuals root from the buried section.
10. Firm lightly and water from below.Draw compost around it and press gently with a fingertip only. Then stand the tray in shallow water until the surface darkens, which settles the compost without washing anything out.
11. Give them two days out of direct sun.Bright but not direct. The disturbed root system cannot yet supply the leaves in full sun, and they wilt. After two days move them back to the brightest place you have.
12. Label as you go.At this stage almost everything looks the same, and you will not remember. Write it at the moment you pot it, not afterwards.

Tips

• Sowing thinly in the first place makes pricking out four times easier, because the roots have not braided together.
• Leggy seedlings can be partly rescued at this stage by burying more stem — it is the only real fix for stretch, and it works on tomatoes and brassicas rather than on everything.
• An old fork with the middle tines bent makes a good pricking-out tool, and a lolly stick works perfectly well.

Common mistakes

• Holding the seedling by its stem — The stem carries everything the plant has. Crushing it is invisible at the time and fatal within days. A seed leaf is expendable.
• Pricking out at the seed-leaf stage — There is not enough root to support the plant through the disturbance. Wait for the first true leaves.
• Leaving lifted seedlings on the bench while you fill pots — Bare roots dry within a minute. Fill and water the pots first, and lift one seedling at a time.
• Firming hard around the stem — It compacts the compost, excludes air and can bruise the stem. A gentle press with a fingertip is all it needs.

If it doesn't work

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