These folks are in the Twin Cities area:
I'd advise you, if you can, to plant them in the ground as soon as you're comfortable doing it. Pick a spot that gets a lot of sun, has something for the bines to climb, and gets a fair amount of water but isn't always saturated.
If you want to put them in containers until you see a little growth, that is ok, too. When it comes time to plant just compress the dirt in the container a bit so that you don't have everything fall apart when you transplant it.
A bonemeal addition to the soil is good, but something else to consider is giving them a good, slow-release source of nitrogen over the summer. I'd recommend some bloodmeal.