Calla lilies (Zantedeschia species) are elegant, rhizomatous plants prized for their trumpet-shaped blooms and glossy foliage. These perennials form dense clumps over time, and regular division is necessary maintenance to ensure their continued health and vigorous flowering. By separating the underground storage organs, called rhizomes, gardeners can relieve overcrowding, rejuvenate mature plants, and propagate new ones. Understanding the proper timing and technique is paramount to successful re-establishment.
Recognizing When Division is Necessary
A calla lily clump signals its need for division through visual cues and a decline in performance. The most noticeable indicator is a significant reduction in the quantity or size of the flowers produced. This occurs because the dense mat of rhizomes competes intensely for finite resources like water, nutrients, and space in the soil.
The clump also becomes visibly congested at its center, resulting in dense foliage with fewer open spaces. This overcrowding restricts necessary air circulation and light penetration, causing plants to look stunted compared to previous seasons. While division is often performed every three to five years as a preventative measure, these signs of decline are the primary drivers for intervention. Ignoring these signals can lead to decreased blooming and increased susceptibility to fungal diseases due to poor air movement.
Determining the Best Time for Division
The most appropriate time to divide calla lilies is when the plant is in a state of natural dormancy, minimizing stress. For most deciduous varieties, this optimal window occurs in late fall after the foliage has died back, or in early spring just before new growth emerges. Dividing during dormancy allows the rhizomes to heal and settle before the heavy energy demands of the growing season begin.
In cooler climates (USDA hardiness zones 7 and below), rhizomes are typically lifted in the fall for winter storage indoors. Division is performed immediately after lifting and cleaning them. Conversely, in warmer zones (8-10), where the plants remain in the ground year-round, division is often performed in early spring as the ground becomes workable, or in the fall once the plant has finished blooming and entered its rest period.
Semi-evergreen varieties, such as Zantedeschia aethiopica, may not exhibit a pronounced dormancy. For these, division is best scheduled during their least active period, usually late summer or early fall, following their main bloom cycle.
The Process of Dividing Calla Lily Rhizomes
Begin by carefully lifting the entire clump from the soil, using a garden fork or spade several inches away from the plant’s perimeter. This wide arc helps avoid accidental damage to the rhizomes and root mass. Once lifted, gently brush or rinse away excess soil to expose the rhizomes and their natural points of attachment.
The rhizomes can often be separated by hand, gently pulling apart the individual growth sections. If the clump is too dense, a clean, sharp knife or sterilized shears may be used to cut the rhizomes into smaller pieces. Each resulting division must contain at least one visible growth bud (or “eye”) and a portion of the root system to ensure successful establishment.
After cutting, allow the freshly cut surfaces to dry and form a protective callus for at least a day in a shaded, well-ventilated area. To prevent fungal infections, dust the cut surfaces with a fungicide powder, sulfur powder, or ground cinnamon. The prepared rhizomes are then ready for immediate replanting, placed at a depth of about four inches with the growth eyes oriented upward.
Ensuring Successful Establishment After Division
Post-division care is important for encouraging the newly separated rhizomes to develop robust new root systems. After replanting, thoroughly water the divisions to settle the soil and eliminate air pockets. This initial deep soaking must be followed by consistent moisture management.
The soil should be kept evenly moist but never waterlogged, as this quickly leads to rot in the vulnerable rhizomes. Placing the newly planted divisions in a location that receives bright, indirect light or partial shade is beneficial during establishment.
Avoid applying fertilizer immediately after division, as the raw cuts need to heal before the plant can process nutrients. Fertilization should be delayed until new foliage visibly emerges, indicating successful rooting and active growth. If division was performed in the fall, newly planted divisions in colder zones require a protective layer of mulch, such as straw or shredded leaves, to insulate the rhizomes from freezing temperatures.