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!
Steve