Calla lilies (Zantedeschia) are prized ornamental plants native to Southern Africa. They are grown from underground storage organs called rhizomes, which are often mistakenly called bulbs. Post-bloom care ensures the plant directs all available energy back into these rhizomes. This energy storage guarantees a robust plant and an abundant display of blooms in the following growing season.
Immediate Post-Bloom Pruning
When the colorful spathe begins to fade, turn green, or wilt, remove the spent flower stalk, a process known as deadheading. The primary purpose of this action is to prevent the plant from diverting resources into producing seeds, rather than encouraging new blooms.
To deadhead correctly, locate the stem of the spent bloom and cut it as close to the base of the plant as possible, near the soil line. Cutting low minimizes the chance of leaving a hollow stub that could collect water and lead to rot. This pruning redirects the plant’s focus toward strengthening the underground rhizome. The green leaves must remain untouched at this stage to continue their work.
Maintaining Foliage for Energy Storage
Once the spent flowers are removed, the green foliage enters a period of energy production that determines the quality of next year’s bloom. The leaves capture light energy through photosynthesis, converting it into starches and sugars. These nutrients are then transported and stored within the rhizome.
During this phase, the plant requires consistent moisture to support photosynthesis, but the soil should never become waterlogged, which can lead to rhizome rot. Continued exposure to sunlight, either full sun or partial shade, is necessary to maximize energy conversion.
Gardeners should stop applying high-nitrogen fertilizers after blooming, as nitrogen encourages new leaf growth at the expense of rhizome development. Instead, a low-nitrogen, high-phosphorus fertilizer can be applied, or feeding can be stopped, to promote the storage of carbohydrates. Allowing the foliage to remain green and productive directly correlates with a larger, healthier rhizome the following season.
Preparing the Plant for Dormancy
The transition to dormancy is a natural process for Calla lilies, triggered by cooling temperatures or a reduction in water and light. This resting period is necessary for the rhizome to consolidate its stored energy reserves. The onset of dormancy is indicated when the leaves begin to yellow and die back naturally, showing that nutrient transfer to the rhizome is nearing completion.
Once the foliage begins to yellow, generally in late summer or early fall, gradually reduce the frequency of watering. Withholding water encourages the plant to enter its resting state, and fertilizer application must be stopped. After the foliage has completely browned and withered, it can be cut back to just an inch or two above the soil line. This final cut prepares the plant for either remaining in the ground or being lifted for storage in colder regions.
Lifting and Overwintering Rhizomes
In colder climates, Calla lily rhizomes cannot survive freezing ground temperatures and must be lifted for winter storage. The best time to dig the rhizomes is shortly after the first light frost has killed and browned the foliage, ensuring maximum energy has been stored. After carefully lifting the rhizomes, excess dirt should be brushed off, but they should never be washed, as moisture promotes rot.
The rhizomes must go through a curing process to toughen their outer skin and prevent fungal infection during storage. Lay the rhizomes in a single layer in a warm, dry, well-ventilated area, avoiding direct sunlight, for four to seven days. Once cured, they should be stored in a breathable material like peat moss, vermiculite, or a paper bag to allow air circulation. The ideal storage location is dark, dry, and cool, maintaining a temperature around 50°F (10°C). Periodically checking the stored rhizomes for signs of shriveling or mold ensures they remain viable until replanting in the spring.