You should start them indoors ASAP, to give them a headstart on growth - you can set them out during the day if it's above freezing there, but bring them in at night if there is any risk of frost. Most people start them indoors anywhere from March through April, under lights optimally, or at least in a sunny window.

If you are going to give them a head start .. plant them in pots .. water minimally until growth appears as you dont want the rhizomes to rot. I put a clear plastic bag over them to maintain some humidity until their is growth. Bottom heat is also helpful.

I start my Canna in late March for a August bloom. The calla were sprouting early this year so I also potted them up in the beggining of April.Both are easy to overwinter. Just put them in a cool dark place in peat moss and wait for spring.

I usually forget to plant my cannas in pots so they go straight in the ground in late May. They start blooming in late August/September. They're kind of nice fall colour but it doesn't last long when the frost comes. Best to start them ahead of time.

I plant callas and cannas in containers/planters and in the fall, I put the whole container in my cold storage. In spring, usually Feb to Mar, I bring the pots out and all I do is water them. I like the look of planting a canna lily in the center of large pots and then planting nico (from the family plectranthus) all around to fill in the bottom. I divide the cannas in the spring rather than the fall. About every 2 years I take the whole pot apart and divide the canna up. I found that when I stored the cannas in peat moss that they dried out too much. That is why I just put the whole pot in the cold storage area.

You can also grow cannas in the pond. Pot them up as you would other pond plants and set in the water with the tops above the surface. Don't put them in until they've sprouted and wait until the water warms up.