The graceful, curving blooms of (Zantedeschia spp.) are a staple at florists, and make an attractive addition to your own home-grown bouquets. Callas grow outdoors in U.S. Department of Agriculture plant hardiness zones 8 through 11, and in other climates you can treat them as an annual or dig up and store the bulbs indoors over winter.
You can cut callas any time while they're in bloom, but it is best to cut them on the day they open. They'll last longer if you cut younger blooms, so make sure you cut callas before the pollen on the stalk in the center of the flower starts to shed.
Use a clean, sharp tool to cut calla lily flower stems. Make cuts near the base of the plant, so the cut stem won't be sticking up. Removing flower stems does not hurt the plants. The only other pruning that calla lilies require is removal of leaves as they turn yellow and die.
As soon as you cut a calla lily stem, place it in a container filled with 2 inches of lukewarm water. Take a container with water in it out with you to the cutting garden.
The water in this container, and in the container you use when arranging calla lilies, should contain a flower food solution. These are available commercially in garden centers and craft stores, or you can make your own. Mix 1/2 teaspoon sugar, 1 teaspoon of lemon juice, a few drops of bleach and 4 cups of water to make a flower food substitute.
When you're ready to arrange callas, pour 2 inches of a water and flower food solution into the vase. When you cut calla stems to the desired length for your arrangement, make all cuts underwater. Only remove the stems from the water when moving them from one container to another.
Calla flowers should last for seven to 10 days after cutting. Check the water level in the vase daily, and add a flower food and water mixture as-needed to keep the water level at 2 inches deep.