Indoors or out?

Outdoors - they'll be dead. Even if the cold temps don't get them, or the cold and damp soil rot them out, the frost will toast them....we have a ways to go before the major danger of frost is past. You could put them in a cold frame, I think - though I'm not too familiar with that, as I've never had one, so can't really advise regarding that.

Indoors - normal room temp is fine.

I winter sowed mine in March. They are now up. We did get some below freezing nights after they germinated and they were touched by the frost but they are still doing well. Marg

Marg....
That is the answer I was looking for! LOL I need to move mine out to my unheated hoop house...they need to be separated and there is no more room in my house! :-)
Looks like I'm a zone warmer than you...so hopefully they will be ok. (our nights are in the mid 30's right now).
Thanks again,
Linda

Linda: When I winter sow I put the pots into flats. Both the domes and flats have holes for drainage and air circulation. This time I used 4-cell seeding pack and put that in the trays. The domes help insulate them. It's an easy way to do it. This is my first time trying it and it seems to have worked so well, I will always do it this way from now on. By the way, there are gardeners in colder zones than me and they also do it. Good luck! Marg

Marge,
I live in West Michigan and put petunias in flats outside under frost cloth and sprinklers the 2nd week of April. The sprinklers are low volume(1/4gpm) and are connected to a simple 24V thermostat/ irrigation valve that turns them on at 34 degrees. They form a protective ice layer over the covered plants. The water gives off a couple degrees of heat as it freezes. Sprinklers stay on until temp goes above 36 degrees and the ice coating is crumbly. I have run sprinklers for a week straight with temps as low as 25 degrees with no problems.
Be aware that poly cold frames offer little protection from freezing inside. Commercial houses have 2 layers of plastic film that has a small blower inflating air between them; creating an insulating effect.