Calla lilies, botanically known as Zantedeschia, are beloved for their elegant, trumpet-shaped flowers and striking foliage. While originating in South Africa, these plants are often assumed to spread aggressively. The direct answer is yes, they spread, but through multiplication and clumping rather than invasive running. Understanding this growth habit is necessary for managing their density or intentionally increasing their numbers.
The Mechanics of Calla Lily Growth
Calla lilies grow from fleshy, underground structures called rhizomes, which are horizontal stems that store nutrients. The rhizome is the engine of the plant’s growth and reproduction. Over time, the mature rhizome produces new lateral buds, often referred to as offsets, pups, or bulblets, along its sides.
These offsets are essentially clones of the parent plant, developing their own roots and foliage right next to the original rhizome. The multiplication of these offsets causes the initial single plant to slowly expand into a dense cluster, a process known as clumping. This is different from plants that spread using runners, which send out long stems to establish new plants many feet away.
While clumping is not typically invasive, it can lead to overcrowding within a confined space after a few growing seasons. A single rhizome can expand to cover a diameter of about one foot. The rate of multiplication and the overall health of the clump are significantly influenced by environmental factors, such as moisture and soil richness. Favorable conditions, particularly consistent moisture and well-draining soil, optimize reproductive growth and lead to quicker formation of dense clumps.
Managing Unwanted Clumping
The natural tendency to form dense clumps requires intervention to prevent overcrowding and maintain plant health. Division is necessary when flower production declines, blooms become smaller, or the center of the plant begins to die out. This process is best performed during the plant’s dormant period, either in the fall after the foliage has died back or in the early spring before new shoots emerge.
Begin the process by carefully digging around the perimeter of the plant using a garden fork or spade, starting about six to eight inches away from the base to avoid damaging the rhizomes. Gently lift the entire clump out of the soil and shake off the excess dirt to expose the individual rhizomes. Using a clean, sharp knife, separate the rhizomes, cutting away any sections that are soft, discolored, or appear old and spent.
Unwanted or discarded rhizome pieces should be disposed of to prevent accidental growth, especially if Zantedeschia is considered aggressive in your region. The remaining sections intended for replanting or storage should air-dry in a cool, ventilated space for one to two days. This permits the cut surfaces to form a protective layer, or callus, which reduces the risk of fungal infections and rot once they are back in the soil.
Encouraging Propagation for More Plants
For gardeners who want to expand their calla lily display, the plant’s clumping habit is easily leveraged for intentional propagation. The most effective method is through rhizome division, which turns a single crowded clump into several new, healthy plants. This intentional separation is best done in late winter or early spring just before the period of active growth begins.
After carefully digging up the rhizome clump, gently brush away the soil to clearly identify the growth points, which appear as small, bumpy protrusions or “eyes.” The large, fleshy rhizome should be cut into smaller sections, making sure that each resulting piece possesses at least one viable eye. Using a sterile cutting tool is recommended to prevent the transfer of any pathogens to the new plant material.
Dusting the freshly cut surfaces with a natural fungicide, such as garden sulfur, can help prevent disease. The pieces should then be allowed to dry for up to 48 hours to fully callus before being planted. New rhizome sections should be planted with the eye facing upward, covered with three to four inches of soil. Spacing the new plants 12 to 18 inches apart allows enough room for multiplication without the need for immediate re-division.