Calla lilies grow from a tender perennial rhizome. The plant cannot tolerate freezing, so in areas with cold winters it must be dug up and stored until warmth returns in the spring. In areas with mild winters, including USDA hardiness zones 8 through 11, calla are left year around in the garden beds. Calla lilies are also sometimes grown as houseplants, thriving for many years in a flower pot indoors. Whether grown outdoors or in, caring for your calla lily properly is vital if you want it to grow and flower each year.
Prior to planting calla rhizomes in the spring, apply a 2-inch layer of compost over the bed and till it into 6 inches of soil. The area should receive at least six hours of sunlight a day. Calla lilies grow best in full sun.
Plant the rhizomes about 4 inches deep and from 1 foot to 2 feet apart.
Fertilise garden calla lilies in the spring or just prior to planting with a 5-10-5 analysis fertiliser. Apply 0.907kg. of fertiliser per 100-square-feet of bed, sprinkling the fertiliser between the plants. Reapply this fertiliser at the same rates every other month while the calla are actively growing.
Lay a 2-inch layer of organic mulch, such as wood chips, around the calla lilies in the spring once the soil begins to warm. Mulch prevents weeds from growing while helping to keep the soil moist.
Water the calla lilies once weekly or more often if the soil begins to dry during hot periods in summer. Water until the soil feels moist to a 6-inch depth when you stick your finger into it.
Store garden calla rhizomes in areas with freezing winters once the foliage begins to die off after the first fall frost. Cut the foliage off 2 inches above soil level, then dig up the rhizomes. Set the rhizomes in a warm, well-ventilated room for one to two weeks to dry, then place them in shallow boxes of dry peat moss. Store in a dry, 40 to 50 degree Fahrenheit room until spring replanting.
Plant calla lilies in a pot with well-drained potting soil that is rich in organic matter.
Place the calla lilies in a south-facing window or other sunny location.
Fertilise potted calla lilies once monthly while they are growing with a balanced liquid houseplant fertiliser, following the rate recommended on the package.
Water the calla lilies when the soil surface just begins to feel dry, watering from the top of the pot until the excess moisture begins to drain from the bottom.
Calla lilies bloom for about four weeks in the summer. Plant calla rhizomes in the garden after all frost danger has passed in the spring.
Avoid getting fertiliser directly on the calla lily plants or rhizomes, as the fertiliser can burn or even kill the plants. Watering after fertilisation washes off any fertiliser that may have splashed onto the plant.