When to start Dahlias

I've bought a couple of Dahlia tubers. I'm unsure of the appropriate time to place them into a container of moist compost to encourage cuttings? Is it now, March or April? Thanks.

I'll be hauling mine out of the cold storage in March and potting them so they get a head start. If I wait to plant them directly outside, they tend to flower just as the fall frosts hit  If I buy any new ones between then, I'll pot them right away as they'll already be sprouting from warm shops.