What can be in an unheated greenhouse?

My sweet peas have been outdoors for a few weeks now, cauliflowers in the ground since mid-February (under a mini polytunnel at first, fleece for the past few weeks). I've got some spare Winter Density lettuces outdoors, but the main lettuces will only be going outside in early April.

To answer your question directly, this is what I'd do:
Onions (Red Baron, Ailsa Craig, Welsh Bunching) - greenhouse or outside
Leeks (not many - had rubbish germination) - greenhouse or outside
Cabbages - greenhouse
Lettuce/salad mixes (have a container of salad in the greenhouse now, but that was started out there) - greenhouse
Tomatoes - indoors
Sweetpeas - no idea
Cauliflowers - greenhouse
Artichokes - greenhouse
Allium (yes, singular - I didn't do well with these!) - greenhouse or outdoors
Zinnias - no idea, but I'm guessing greenhouse
Tomatillos - indoors
Cucumber - indoors definitely
Watermelon - indoors definitely
Lemongrass - indoors definitely
Radishes - out!
Mustard - greenhouse
Kohlrabi - out
Chillies - indoors definitely
Aubergines - indoors definitely

I haven't got all of these types sowed yet, and I've not grown caulis before, and I am by no means an expert so do tell me if you disagree

Brilliant, this is exactly what I need! Thank you.

This is going to create lots more space for the next round of sowing

Ideally you would put them on staging in the greenhouse as, on the floor, slugs can be a big problem with little seedlings. I've got onions. leeks, brassicas, beetroots and lettuce out.we've had several frosts and I've accidentally left the door open a few nights and they are all coming along nicely.
The onions and leek are only like blades of grass in seed trays but I'd like to get them planted out. I did this last year and got a bumper crop of both with not too much effort (sow the seeds, plant out, hoe a couple of times then harvest).

Thank you! I do have one bit of staging, but it will only carry so much. I may have to try and make some more from the fitted wardrobes I took out of the house.

What a lot you’ve got. Lucky you.
My zinnia are not sprouting at all.

The ones I bought from Lidl are doing really well, but I've not had any luck with the Orange King seeds from the swap just yet. Hoping they just need a little bit longer, but I may have kept them a bit wet. I may try sowing some more if there's nothing doing in the next few days.

Don't blame yourself, it's more likely that I didn't let the flower heads dry out enough or the seed didn't develop properly. Gosh they were a real faff to extract the seed from!

Ah, but that's some of the joy of sharing seeds like this. Not knowing quite what you'll get or if you'll get anything at all. If my solitary allium survives my ongoing care, it will give me far more pleasure than if I'd had a hundred germinate from a bought packet. It's why I'm gutted that I managed to kill all the Echinacea Pow Wow Wild Berry seeds that germinated - I had three sprout, but I found it impossible to keep them just the right side of wet. Two dried out and one I watered too much! But there's always next year

I think I kept a few Orange King seeds back. Think I may sow them today! (Doing another online training day, so will have a lunch break at home)

Just catching up with last week's Gardeners World on the BBC. This lady made me realise what's missing from my greenhouse!

   

No no, I don't need the lady. But a lounger for the good Mrs H to repose on? Might just be able to squeeze that in!