Answer: Zantedeschia, the calla lily, prefers to be somewhat crowded, so I'd suggest waiting to see how they perform this year. If blooms are sparse they can be divided. If they bloom well, they do not require dividing. When you decide it's time to divide, wait until fall, they dig, divide, and set rhizomes 2" deep and 8"-12" apart in organically enriched, well draining, slightly acidic soil.
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