To answer the question of whether Calla Lilies (Zantedeschia spp.) are annuals or perennials, we must first look at their fundamental botanical characteristics. Calla Lilies are herbaceous perennials. This means they possess the biological capacity to live for more than two years, dying back to their underground storage organs at the end of each growing season and regrowing when conditions become favorable again. The key to their perennial nature lies in their rhizomes, which are thickened, fleshy underground stems that store energy in the form of starches and nutrients. This stored energy allows the plant to survive periods of dormancy, typically triggered by cold or drought, and fuels new growth when the cycle begins anew.
The perennial status of a Calla Lily is not absolute but is entirely dependent on its environment, specifically winter temperatures. The plant's survival hinges on the rhizome not freezing. If the ground freezes solid, the water within the rhizome's cells will freeze, forming ice crystals that rupture the cell walls and kill the plant. Therefore, whether a Calla Lily behaves as a perennial or an annual is a direct result of the minimum winter temperatures in a specific region. This makes them "tender perennials" in horticultural terms, meaning they are perennial in warm climates but cannot survive cold winters without human intervention.
Understanding the USDA Plant Hardiness Zone system is essential for applying this regional guide. These zones are defined by the average annual extreme minimum winter temperature.
In USDA Hardiness Zones 8 through 10, where winter temperatures rarely, if ever, dip below 10°F to 20°F (-12°C to -7°C), Calla Lilies thrive as true perennials. Gardeners in these regions (such as parts of the Pacific Northwest, California, and the Gulf Coast) can plant the rhizomes directly in the ground. After the flowering season concludes, the foliage will naturally yellow and die back. The rhizomes remain dormant in the soil throughout the mild winter, protected by a layer of mulch, and will reliably send up new shoots the following spring.
In Zone 7 and colder regions (including much of the Midwest, Northeast, and mountainous areas), Calla Lilies cannot survive the winter in the ground. Here, they are typically treated as annuals. Gardeners plant the rhizomes in the spring after the danger of frost has passed, enjoy their spectacular blooms throughout the summer, and then allow the plant to be killed by the first hard freeze. Alternatively, to preserve the plant's perennial nature, the rhizomes can be lifted and stored. After the first frost blackens the foliage, the rhizomes are carefully dug up, the soil is brushed off, and they are allowed to cure (dry) for a few days in a well-ventilated area. They are then stored in a cool (around 50°F / 10°C), dry, and frost-free place, such as in a box of peat moss or vermiculite, for replanting the next spring.
For gardeners in colder climates, growing Calla Lilies in containers offers a flexible solution. The plants can be enjoyed on patios and decks during the summer. When the foliage dies back in the fall, the entire container can be moved to a cool, dark place like a garage or basement where it will not freeze. The soil is kept mostly dry throughout the winter. In the spring, the container is brought back into the light, watering is resumed, and the perennial cycle continues without the need to dig up the rhizomes annually.
