When/where can I plant out the following...?

Hi LewaK.
Ok, lets take it a step at a time.
1. Don't worry about your carrots, they will probably do quite well as long as they get some decent sun for at least part of the day. I would probably sow some more further up the garden if you have room (give it a couple of weeks before you do) as you will then be successional sowing and extending your cropping season!
2.Your Onion seedlings are still a bit infant to risk doing anything with other than keeping them damp and telling them how well they are doing!
They will need to be fully unfurled and starting to thicken up (a bit like chives) before they go outside during sunny, calm weather (they won't like a cold wind) for hardening off. That'll take a few days.
3.Your peas will be quite happy against a fence as long as they get plenty of water (fences and walls can get very dry at the base) They will tolerate a bit of shade, but most things that produce fruit like lots of sun. Give them another week or two before hardening off and then planting them out. They should be about two inches high. They are quite tough little beasts, but if they have been cosseted in a nice warm lean-to then they will probably appreciate a little protection at night for the first couple of weeks. I use cut down pop/mineral water bottles as mini cloches
4.Peppers are notoriously slow to germinate and DO NOT LIKE THE COLD AT ALL -EVER!
(Just so as you know!)
5.Treat your leeks like your onions initally - but I usually grow them on in pots until they're about the thickness of a pencil before separating them and planting indiviually in deeply dibbled hole and just watering them in.
Think that covers everything. No doubt others will be along shortly with more (and better) advice!

should be OK, or sow some more in a pot in the sunshine

They are bent to start with. Let them get to pencil thickness, then plant out

They can go outside now, while still babies. Don't let them get too lanky and soft indoors

They can take up to a month to germinate. Make sure they're warm enough (16c +)

Anything (like peas or broad beans) that was sown and grown indoors - house or greenhouse - should really be hardened off before you put them straight out. Put them outside in the day for a week or so, then outside all the time for another week in a sheltered spot. Then you can bang 'em in.

Thanks for your help, everyone! It's great to have some reassurance :3

Don't want to hijack your thread , but how low a temperature can you let it get to at night before you bring in all the pots that you are trying to harden off ? Not lazy but it's a bit like the hokey cokey here at the moment! Have got pots of broad beans,shallots and mange tout.
Thanks

If they are plants that can normally cope with a frost, if they've had a good week of daytime hardening off I'd let them get on with it, as long as they were in a sheltered area.

Yep, we play the hokey cokey in our house too, from Feb to May. All windowsills are cleared of seedlings at night (they're brought inside the curtains) and everything hardening off is taken into the greenhouse at dusk - and back outside again in the morning, unless the weather is truly vile

It's not worth trying to cheat on the hardening off

I don't do it like that.

I put the plants out, initially, provided the day is "clement". We've had some nice days in East Anglia for the last week, everything has been out. But initially I didn't put them out until about 10am, and they were back in around 5pm.

Now, a week later, they are out by 9am and not in until 6pm (but if there was a heavy frost and air temperature was low, I would delay putting them out; if it was a biting cold wind I would bring them in earlier.)

After a week I will leave them out for the night if the forecast is mild. That will mean overcast and absolutely no chance of a frost. They will be in a sheltered spot against the house - so more protected than they will be once planted out, so more able to cope during the "hardening off" phase.

I'm lucky in that I work from home, so its easy for me to choose what time I put them out in the morning - I just move my "coffee break" accordingly

Harder for folk that have to set off to work at a fixed time. For that I think a coldframe is important as you can open that an amount early in the morning without subjecting the plants to too much cold-shock.

Haven't we? Nice and sunny and about time too. I put the hardening off stuff outside in the sun, because inside the greenhouse is getting too warm for them

My "tender" seedlings (Toms, Peppers and the like) are toasty though - which I think they like.

They are brought in at night and put under my Metal Halide lamp (brought for a different project, now deployed on the seedlings )

Early days, but I'm surprised at how stocky the plants are looking. As new seeds start to germinate and break the surface I'm putting them under the light at night too ... nothing leggy to be seen, so far ...

Stupidly I didn't leave a couple of plants out as a "control test" - the ones I am growing for the in-laws would have been fine, I'm sure