Seedlings

[CuriousOn]

How big should seedlings be before transferring them from trays outside?

There's no exact answer- it's kind of a trade off between root disturbance/establishing being easier if they're small, but they're more vulnerable to pests.
Obviously tender stuff can't go out yet. Gardeners like Charles dowding often plant out hardy stuff pretty tiny at this time of year, covered with a sheet of horticultural fleece to bring them on a bit quicker. But doesn't have a slug problem as his plot is insanely tidy!

If you post which types of seedling, whether you sowed them in a seed tray or modules, and what your plot is like (how weedy, how far north) you could get some more specific advice on here I'm sure.

General rule is you transfer them to small pots when they have a true set of leaves. But still keep them under cover and away from pests until May when you can plant them out.
But refer to your area and seed packet for more information

They're planted in modules, unfortunately when putting in individual modules 3/4 seeds went in and so I have more than one seedling 🌱 in every compartment. I'm in the north east of England

When this happens to me and I end up with more than 1 seedling per module, I choose my favourite and very gently pull the other(s) out and discard.

My favourite will be the strongest and/or the one most centrally located.

I've already potted some of mine on. l do it as soon as they are big enough to handle. Mine are outside now whilst dry and sunny, then l bring them in and leave them in my glass porch, which l double up as a greenhouse at night.

How big before planted outside?

Depending on the type of seed, you can pinch it put to stop it becoming leggy and to encourage side shoots while it's still on the windowsill. I do that with my sweet peas, cosmos, basil and coriander.

Here in the North East, I don't pot on until around mid April, then I move them to a coldframe or greenhouse. Later still for plants slow to get going.

They're wildflowers

“Wildflowers” is a pretty broad church - any more detail than that?

How big before planted outside?

It depends what it is and the weather forecast. Nothing goes outside until it has a couple of sets of true leaves, at the very least. Nothing goes out to stay when there is a risk of frost.

Then it depends how tender or hardy the plant is.

A hardy plant: I would wait until two sets of true leaves then spend a week hardening off. Then probably outside but with a cover on chilly nights. Brought in overnight if frost is a risk.

Packets say 'cornfield mixture' & ''wildlife mixture'

That rule dates from when it was normal to sow seeds in seed trays. So you wanted to prick them out asap, and until you had true leaves they’d be too brittle to transplant.

in general, if they’re sown singly, plant them in something larger when the roots have filled what they’re in at the moment.

Cornfield mixture will be annuals, and won’t want much root disturbance. Leave them till the roots fill what they’re in, harden them off, then plant out.

”wildlife mixture” could be anything, but probably mainly annuals, so treat them the same way.