When I've grown ranunculas is the past, I've soaked the ?tubers? in warm water for about 12 hours, before potting them individually into 3 1/2" pots. Then grown them under cover until April/May, and then planted them out.
I'm not sure if they are fully hardy, but I have one plant (in a very sheltered spot) that keeps coming back, year after year.
valmarg