I think more gardeners should start onions from seed indoors.
The soil must be kept from freezing but I don't need to turn the heat on in the greenhouse. They are out there from February and outta the way by the time other things show up.
I don't allow them to freeze in the yard either but they don't need to be kept warm with the bedding plants.
They really aren't difficult to transplant and take it well. After awhile, here they come!
i've had onions survive winters here for the past 2 years. this past year we got hit with feet of snow that kept them buried. they haven't been getting big but they are still surviving. last year mine went to seed.
I planted stutgardener (sp?) One year from seed. They actually made small onions before the heat scorched them. Usually I set out bundles of onion sets in fall for green onions all winter.