Hi again and seed question

Hi all,
I haven't been around for quite a while, partly because it's been winter, but mainly because I have been having MAJOR works done on the house and my time has been taken up with that.
I've managed to get onto the plot a fair bit in the last couple of weeks and I've been amazed how easy it's been to get the beds weeded and ready this year, so all my hard work over the last 2 years seems to have paid off! 
Anyway, enough rambling, here's the question!
I have some courgette, sweetcorn, cucumber and pumpkin seeds. When would be the best time to sow them, in an unheated greenhouse? Is it still a bit too early? It doesn't say on the packets, just "sow in heat in 3"inch pots blah, blah, blah".
The last couple of years I've always bought small plants from the GC as I never had time for seeds, too busy weeding, digging, crying, swearing.... you get the drift!

Any advice appreciated!

Hi, my advice, buy a propogator it'll change your gardening life.

I'd have thought the seed packets should at least provide some indication of what sort of heat is needed to germinate the seeds.

Things like peppers etc do like a constant, warm temperature and thus the fluctuations and lows of an unheated greenhouse (we're still getting frosts).

Some seeds will therefore want a propagator, others won't.

Can't be much more use on unheated greenhouse sowing times, sorry 

Cukes need heat, and lots of it, to germinate.  Think on a shelf over a radiator in your warmest room.  Squashes are less picky, but still like a warm room.  Sweetcorn ditto, and doesn't like to get pot-bound before you plant it out.  Also, they all grow quickly and will get unmanageable if you try to keep them indoors for more than about a month.  Do you have a min-max thermometer in your greenhouse?  If not, pop out at dawn to see what the overnight drops too - at this time of year it may not be many degrees above freezing.