My Calla Lily Leaves Are Turning Yellow

White calla lily (Zantedeschia aethiopica) is a bulb plant that grows outdoors year-round in U.S. Department of Agriculture plant hardiness zones 8 through 10. This stemless plant grows in clumps. The flowers grow directly from the bulb and can rise to 36 inches on leafless stalks. Each blossom includes a white, showy spathe -- a leaflike bract-- wrapped around a yellow spadix flower that looks like a finger. The leaves are a deep green and shaped like arrowheads.

Hybrid calla lily (Zantedeschia spp.) comes in colors other than white, including pink and yellow, and generally grows in USDA zones 7 through 10, depending on the cultivar.

In its native habitat, calla lily lives in swampland. As summer turns into fall, the swampland dries up and, at the same time, the calla's foliage dies back and the plant goes dormant. A calla in your garden -- planted or potted -- must do the same.

As a calla lily moves into dormancy, its foliage wilts and dies. As it does so, it naturally turns yellow, then brown. If your plant is entering dormancy, yellowing foliage is nothing to worry about. Allow the plant to wilt and enter dormancy. Water it infrequently for the several months it remains dormant. When new growth indicates it is leaving dormancy, begin regular watering again.

Calla lily leaves may turn yellow when it is transplanted. This happens if the plant suffers transplant stress. As the root system develops in the new location, the plant will produce new leaves and you can cut off the yellowed leaves.

Wind can also cause calla leaves to yellow. Plant it in a protected, sunny spot.

Another mistake that causes yellowing leaves on a calla is adding cow manure to the soil. This product causes a salt overdose in the soil. The leaves turn yellow and curl. Your best bet is to remove the plant and plant it in a new area or pot in fresh potting soil.

Calla lily is vulnerable to root rot disease, which can cause yellowing leaves, among other symptoms. Root rot (Phytophthora cryptogea) tends to be a problem in overly wet soil, and occurs most frequently when you grow a calla lily in clay or other soil that does not drain freely. The constantly wet soil causes feeder rootlets rot.

Root rot symptoms often start with the outer leaves, where the leaf margins yellow. This develops into a general yellowing and wilting of the leaves.

The best way to control root rot is to provide your calla lily with well-draining soil. Reducing watering is also helpful. When you are transplanting a calla lily, be careful not to plant it so deep the soil covers the base of the stem, which encourages root rot. If you're planting the calla lily in a container, always use a plant pot with drainage holes.