Calla Lilies (Zantedeschia) are popular flowering plants known for their elegant blooms and foliage. They are not true lilies but belong to the Araceae family, originating from South Africa. Proper fertilization supports vigorous growth and encourages the production of abundant, high-quality flowers. Feeding the plant with the correct chemical balance and timing the application to match its growth cycle are the primary factors in successful cultivation.
Understanding Calla Lily Nutrient Needs
Calla Lilies require a specific nutrient balance to prioritize the development of their signature blooms over excessive leaf growth. The three macronutrients—Nitrogen (N), Phosphorus (P), and Potassium (K)—must be carefully managed. High nitrogen levels stimulate the growth of lush foliage at the expense of flowers. Therefore, the best fertilizer will have a lower first number (Nitrogen) and higher second and third numbers (Phosphorus and Potassium).
A high-phosphorus and high-potassium formulation is recommended for encouraging flowering, such as an NPK ratio of 5-10-5, 3-5-3, or a similar ‘bloom-booster’ blend. Phosphorus is directly involved in the energy transfer required for flower and root development. Potassium aids in overall plant health and disease resistance. Balanced fertilizers like 10-10-10 or 20-20-20 provide equal nutrients but may need supplementation during the pre-bloom phase.
Calla Lilies also benefit from specific micronutrients. Trace elements such as magnesium, iron, calcium, and boron play supportive roles in various plant functions. Calcium is needed to prevent certain nutritional deficiencies that can affect flower production. For potted plants, these micronutrients are especially important because they are not naturally replenished by the surrounding soil.
Selecting the Best Fertilizer Format
The choice between a water-soluble liquid and a slow-release granular fertilizer depends on the gardener’s preference and the plant’s growing environment. Liquid fertilizers are immediately absorbed by the plant since the nutrients are dissolved in the solution, making them instantly available to the roots. This immediate availability is beneficial for quickly correcting a nutrient deficiency or providing a rapid boost during the active growth phase, though it requires more frequent application.
Granular, or slow-release, fertilizers provide a continuous, steady supply of nutrients over a longer period as they dissolve slowly with watering or rainfall. This “set it and forget it” approach is convenient for in-ground Calla Lilies or container plants that can be easily over-fertilized with liquid feeds. However, the nutrients in granular feeds, especially immobile ones like phosphorus, must be placed close to the root zone to be fully effective.
A combination of formats often yields the best results. A slow-release granular fertilizer can be incorporated into the soil at planting or early spring to provide a foundational, continuous feed. A diluted liquid feed can then be used every few weeks to supplement the continuous supply, especially when the plant is preparing to bloom, ensuring immediate delivery of the high-potassium and phosphorus elements.
Creating a Seasonal Feeding Schedule
The Calla Lily’s feeding schedule must align precisely with its natural life cycle, requiring different nutrient concentrations at various stages.
Active Growth Phase
During the Active Growth Phase, which begins in spring when new shoots emerge, the plant has its highest demand for nutrients. For container plants, a diluted liquid fertilizer should be applied every two to four weeks to fuel leaf and stem development.
Pre-Bloom Phase
As the plant transitions into the Pre-Bloom Phase, typically in late spring or early summer, the fertilizer should be adjusted to a high-potassium and high-phosphorus formula to stimulate flowering. Some gardeners switch to a specialized bloom-boosting liquid feed, such as a tomato fertilizer, applied every two weeks until the flowers begin to fade. Over-feeding with nitrogen during this period must be avoided, as it can result in a plant with many leaves but few blooms.
Dormancy Phase
Once the plant has finished flowering, usually by late summer or early fall, the feeding should gradually be reduced and then stopped entirely. This cessation of fertilization signals the beginning of the Dormancy Phase, allowing the plant to prepare for its winter rest. For Calla Lilies grown in containers, this rest period is non-negotiable and requires a dry, cool environment until new growth resumes the following spring.