The cream-white types are most abundant in western Washington. It's also possible to find yellow or pink callas in nurseries, but the cream sorts seem to establish best in gardens. I've seen older clumps near homes in Tacoma growing to 3 feet tall and as wide. If you wish to add them to your garden, the rhizomes are sold in early spring for planting, often appearing in nurseries with other summer-blooming bulbs like lilies and dahlias. Callas will bloom in light shade but require 4-5 hours of sun daily to bloom well.
Callas originate along stream and pool edges in South Africa.
Here in western Washington, they eventually form crowded clumps that should be lifted during September or October. Lack of bloom indicates the need for dividing. You'll find rhizomes piled upon each other. Separate these, add compost to replenish the soil, and set them back in, about 6 inches apart and 2 inches deep. Water well to get them settled, and then depend on fall rains to initiate good root growth for summer next year.