Calla lily (Zantedeschia aethiopica), hardy in U.S. Department of Agriculture plant hardiness zones 8 through zone 10, spends its life as an annual or in containers in many gardens. These South African beauties grace ponds and rain gardens, but they also make impressive cut flowers. Calla has a nasty secret, though, that helps defend against some garden grazers.
Calla lilies are not lilies. They are arums -- members of the Araceae family -- related to Jack-in-the-pulpit (Arisaema triphyllum), hardy in USDA zones 4 through zone 9, and anthuriums (Anthurium andraeanum), hardy in USDA zones 11 through 12. Like other arums, tiny flowers bloom along a stem terminal, called a spadix, where a specialized leaf called a spathe provides shelter for it. Spathes give the calla its distinctive look. Callas grow in full sun to part shade and bloom from June through July.
Offense and Defense
It’s a tough world out there in the garden, especially if you’ve located it near an area where the deer and other foragers roam. Like other plants, calla lily has developed defenses against foraging critters. It produces toxic chemicals that reside mainly in its roots -- and circulate in lesser amounts throughout the plant’s tissue. Oxalic acid, a compound found in arums and other plants -- rhubarb leaves contain it -- cause mouth pain, digestive upset, vomiting, convulsions and other symptoms that can, in small animals, cause serious damage to mouth, esophagus and gastrointestinal tract or death. Oxalic acid asparagine, a protein found in urine, also produces toxic responses.
A hungry herd of deer consumes vegetation according to what’s green and growing in order of tastiness. Deer might taste-test your calla lilies when there are few alternatives. Unless you live in an area where calla lilies are hardy, they are likely to pass on calla’s salad with oxalic acid dressing after a taste. Adult deer weigh nearly the same as humans, but fawns and yearlings could suffer the same effects as children or family pets when consuming parts of the plant. If deer are desperate enough to eat hot sauce, a common repellant, they might try callas. Otherwise, one of the elders of the herd is most likely to try the plant, discover its mouth-stinging properties and move on, leading the herd to safer browsing choices.
Moles belong to the animal order of Insectivora -- they are more closely related to bats and shrews than to rats or mice. They live underground and eat insects, snails, slugs and earthworms, and are both a blessing and curse. They can consume their own body weight in food in a day. The damage they do to a calla lily might be incidental to tunneling -- bumping into the root system while tunneling. Any normally sensitive mole would certainly turn tail quickly because of oxalic acid’s skin and mouth-burning properties. Nevertheless, mole tunnels could conceivably lift plants, exposing crowns to the air. Mole damage is unlikely, however, due to the mole’s carnivorous preferences and the calla roots’ caustic properties.