Traditional callas are cool-soil plants. They are late winter/early spring bloomers here in Northern CA, but your colder winters would be tougher on them. They are cold-hardy only to zone 8.

Once the soil warms up the Zantedeschia aethiopica start going dormant and need good drainage so the rhizomes don't rot. Hybrids like Z. elliottiana and Z. albomaculata like more sun and bloom later, so they are a little better with warm soil, but once the temps hit past 80 they will start fading too.

Short wide pots would work best, I think. Check your rhizomes for rot. Z. aethiopica is by far the most floriferous and strongest; the others are puny bloomers compared to the Aethiopica varieties. I've had the hybrids take 2 yrs to rebloom once in the garden.

Mine did very well in the ground until this past winter when I lost some of the bulbs. I give them alot of water and they get about 7-8 hours of direct sun. I have the red ones, which are the ones I think I lost and the yellow ones, which are planted in the same bed, and are actually younger than the red ones. They made it fine through this winter. My wife has hers in the front yard, ibut she gives them less water than I do. Hers flower, they're just shorter than mine in the back yard. Hope this helps.

This advise is helpful. Today, I put my other calla lily outside today (still in the pot) just to see how it would do. It didnt do so well. It started to wilt after a couple hours in the sun. I had to bring it in. I have decided to keep them in bigger pots and change the soil each year. (Thanks for the website).