I got this off the internet: "Although calla lilies are known as 'spring bulbs,' in tropical climates or USDA zones 8-10, calla lilies thrive outdoors year-round. They can be planted at any time!
In other areas, they can be planted when temperatures rest higher than 55 degrees F (below 55 degrees, calla lilies stop growing). Just make sure that there is no danger of frost or of temperatures dropping below 55 degrees in the first 12 weeks after planting". I live in TN, I planted mine in the shade and I bring it in in the winter.