When to separate calla lily bulbs?

Calla rhizomes need to be split after they've finished blooming and leaves turn yellow or die off. The rhizome needs a chance to dry out before being split. For the colored variety, be very careful not to let it sit in moisture or they may rot! Take them out of the soil and set them in a dark, dry place for a few days. Then, pry the rhizomes apart.

For the larger, white calla (prefers moist soil), it won't rot. I would still recommend letting it dry out a bit before separating the bulbs.