Cut all the foliage and flowers down to about 1 inch above the soil line. Use sharp shears to cut through the fleshy foliage.
Place a shovel or garden fork 6 inches from the edge of the calla lily colony. Press down on the shovel to sink it into the ground then pull back on the handle to lift the rhizomes from the soil.
Brush off the soil from around the main rhizome clumps, and place them in a basket or bucket for easy removal from the site.
Continue digging out and removing the calla lily rhizomes throughout the area.
Go back through the area and carefully search for any pieces of the rhizome. Sections left in the soil will sprout in the next growing season and will quickly multiply.
Remove any new plants that were missed each growing season. Calla lilies are difficult to eliminate, and it make take several years to remove them completely.