The Calla Lily, a member of the genus Zantedeschia, is a popular ornamental plant known for its striking, trumpet-shaped flowers and elegant foliage. Its sophisticated appearance often leads to the common misconception that it grows from a traditional bulb, a term frequently applied to any plant with an underground storage organ. While many elegant flowering plants, such as tulips and daffodils, are true bulbs, the Calla Lily relies on a different, distinct type of subterranean structure.
The Calla Lily’s Underground Structure
The Calla Lily develops from a structure classified as a tuber or, for some species, a tuberous rhizome. This organ is a swollen, modified stem that grows beneath the soil surface. It acts as the plant’s primary reservoir, storing starches and other nutrients to sustain the plant through dormancy and fuel its vibrant blooming season.
The structure is not uniformly round like a typical bulb but is often lumpy and irregular in shape. Regardless of the exact classification (tuber or rhizome), the core function remains the same: it is a solid piece of stem tissue. This solid structure is distinct from the layered composition of a true bulb and is important for understanding how to properly plant and care for the Calla Lily.
Distinguishing Tubers from True Bulbs and Corms
A true bulb, exemplified by an onion or a tulip, is a miniature plant encased in layers of fleshy, modified leaves. When a true bulb is cut open, these concentric scales are visible, all attached to a compressed, flat stem at the base called the basal plate. This basal plate is where the roots develop, and the bud for the next season’s flower is contained within the center of the layers.
A corm, such as that of a gladiolus or crocus, is also a modified stem, but it is solid throughout, lacking the fleshy, layered scales of a true bulb. Corms are typically covered by a dry, papery tunic and also feature a basal plate for root emergence. The old corm is consumed during the growing season and is replaced by new corms that form on top or alongside the original structure.
The Calla Lily’s tuber or tuberous rhizome is fundamentally different because it is a mass of swollen stem tissue. It lacks both the layered scales of a bulb and the distinct basal plate of a corm. New growth, or “eyes,” can emerge from various points on the surface, rather than being confined to a single central bud.
Planting and Orientation of the Calla Tuber
The unique structure of the Calla Lily tuber dictates a specific planting strategy for successful growth. The tubers should be planted relatively shallowly, typically covered by only two to four inches of soil. This depth is significantly less than what is required for many true bulbs.
Determining the orientation can be challenging due to the irregular shape. Growers should identify the small, knobby growth points, or “eyes,” and ensure they are facing upward in the planting hole. If the growth points are not obvious, the tuber can be planted flat, as the shoots will generally find their way to the surface. The plant thrives in rich, well-drained soil, as excessive moisture can quickly lead to rot.
Storing Tubers During Winter Dormancy
In regions where winter temperatures drop below freezing, Calla Lily tubers must be lifted from the ground and stored to prevent damage. This process begins after the foliage has naturally yellowed or after the first light frost signals dormancy. The tubers should be carefully dug up and the excess soil gently removed.
The tubers require a curing period, drying in a well-ventilated, warm location for a few days to a couple of weeks. This step toughens the outer skin, protecting the stem tissue from rot during storage. Once cured, store the tubers in a cool, dry, and dark environment, ideally between 50 and 60 degrees Fahrenheit. Using a medium like dry peat moss, vermiculite, or a paper bag helps maintain air circulation and prevents desiccation until spring replanting.