Answer: Calla lilies (Zantedeschia) grow from rhizomes (thickened roots) and can grow into clumps if left undisturbed for a few years. You can divide callas during the dormant season after the leaves have died down and the plants are resting. In the late winter/early spring just before new growth begins is a good time. Dig the rhizomes (or unpot) and divide by breaking apart the mass. You'll be able to see individual rhizomes once the soil has been brushed or washed away. If there is a cut, allow it to harden off for a day or so before putting back into soil, or dust with a fungicide to prevent disease from entering.
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