If they are still just rhizomes, then you might want to get them started right now in a pot of soil placed somewhere inside near some heat. Then once they are sprouted and it gets warmer outside, you can plant out. It's usually recommended to do so no earlier than your last frost date, but consider that the ground may still be cold early on and it would be better to do it around when you might normally plant tender summer annuals and veggies when the soil has warmed up.