A unheated greenhouse is ideal, the only thing is that you'll have to do the watering.

What I do is wintersow outdoors as usual, once you see sprouts, take their tops off and take them into the g/h to further their growth.

It gets really hot in the g/h, make sure you check on them everyday.

Its a good idea to shut the door and all vents if a early spring frost is predicted.

Sharon