Calla Lilies do not grow from true bulbs, but from a type of underground storage structure called a rhizome. While often mistakenly sold and referred to as “bulbs” in the gardening trade, the Calla Lily’s botanical structure is distinctly different. Understanding this specific structure is fundamental to providing the correct care, especially regarding planting, cultivation, and overwintering the plant.
Defining the Calla Lily Rhizome
A rhizome is botanically defined as a modified, horizontal, underground stem. This stem functions as a storage organ, accumulating starches and nutrients that sustain the plant through its dormant period. Unlike a true bulb, which is a modified leaf structure composed of fleshy scales, a rhizome is a thickened stem that grows sideways beneath the soil surface.
This structure allows the plant to spread horizontally, producing new roots downward and new shoots, or “eyes,” upward from its nodes. The Calla Lily rhizome is a tuberous perennial—a thickened, compact storage stem that is somewhat irregular or lumpy. This dense, fleshy mass is highly susceptible to rot if kept too wet during its rest cycle, which influences handling and storage.
The nutrient storage mechanism in the rhizome provides energy for the plant’s next growing cycle, emphasizing the importance of proper dormancy. The distinction between a rhizome and a bulb centers on whether the storage material is stem tissue or leaf tissue.
Planting and Cultivation Essentials
Successful growth begins with planting the rhizome in the spring, after all risk of frost has passed. Calla Lilies thrive best in rich, well-drained soil, as the fleshy rhizome easily rots if left sitting in soggy conditions. Incorporating organic matter enriches the soil while improving drainage to prevent water retention.
The rhizome should be planted shallowly, typically between 3 and 4 inches deep when placed directly into the garden. Ensure the “eyes,” or growing points, are facing upward toward the soil surface. After planting, the area should be watered thoroughly to settle the soil around the rhizome.
Calla Lilies prefer full sun to partial shade, though they benefit from afternoon shade in regions with intense summer heat. During the active growing season, the plants require consistent moisture to support their lush foliage and blooms. Allowing the top layer of soil to dry slightly between waterings avoids over-saturation near the vulnerable rhizome.
Winter Storage and Dormancy
In regions where winter temperatures fall below freezing, the Calla Lily rhizomes must be lifted and stored, as they are not reliably cold-hardy. The process of preparing for dormancy should begin in the fall, once the foliage has started to yellow and die back naturally, or immediately following the first light frost. This allows the plant to pull back maximum nutrients into the rhizome before being disturbed.
After gently digging up the rhizomes, avoid washing them with water, which can introduce moisture and encourage rot during storage. Instead, gently brush off any excess soil and cut the remaining foliage down to a couple of inches above the rhizome. The rhizomes must then be cured by placing them in a warm, dry, and well-ventilated location for approximately four to seven days. This curing process toughens the outer skin, creating a protective layer.
Once cured, the rhizomes should be stored in a dark, cool environment, such as a basement or unheated garage, where the temperature remains consistently between 45 and 55 degrees Fahrenheit. Placing them in a paper bag or a box filled with dry peat moss or wood shavings helps maintain a stable, low-humidity environment. Checking the stored rhizomes periodically for signs of shriveling or mold will ensure they remain firm and healthy until they are ready to be replanted the following spring.