The calla lily (Zantedeschia) is a popular choice for its striking, trumpet-shaped flowers and glossy foliage. When these plants fail to bloom, gardeners often see lush leaves but no colorful spathes. Diagnosing the lack of flowering requires a structured look at the plant’s environmental conditions, soil nutrition, and life cycle. This approach helps pinpoint the specific cause and guide corrective action to encourage vibrant blooms.
Light, Temperature, and Location
The amount of light a calla lily receives is a primary driver of flower production. Insufficient light causes the plant to focus energy on growing foliage rather than developing flower buds. In cooler climates, calla lilies thrive in full sun, requiring at least six hours of direct sunlight daily for abundant flowers.
In regions with intense summer sun, the plant benefits from afternoon shade to prevent leaf scorching. The ideal temperature range for active growth and blooming is consistently between 60 and 80 degrees Fahrenheit; temperatures below 50 degrees Fahrenheit cause the plant to slow down or enter dormancy prematurely, halting flowering.
Soil Composition and Nutrient Ratios
The physical and chemical makeup of the soil directly influences the plant’s ability to bloom. Calla lilies require rich, well-draining soil, with a slightly acidic pH range of 6.0 to 6.5 being generally ideal. While they naturally prefer a moist environment, any soil that becomes waterlogged will quickly lead to rhizome rot, which is fatal and prevents any energy storage needed for flowering.
A common mistake that suppresses blooming is the excessive application of nitrogen (N) fertilizer. Nitrogen promotes vigorous vegetative growth, resulting in large, dark green leaves at the expense of flower development. To encourage flowering, the focus should shift to phosphorus (P), the middle number in the NPK ratio, which is essential for root and bloom production. During the active growing season, applying a balanced fertilizer, such as a 10-10-10 or one specifically formulated for flowering bulbs, will support the plant without over-fertilizing the foliage.
Dormancy and Watering
The most frequently overlooked cause of non-blooming is the plant’s requirement for a period of dormancy, or a dry rest cycle. As a tender perennial, the calla lily’s rhizome needs this rest to consolidate energy reserves for the following season’s bloom cycle. Without this necessary rest, the plant remains in a continuous vegetative state, and no flowers are initiated.
To trigger dormancy, watering must be intentionally reduced or stopped in late summer or fall as the growing season winds down. The foliage will naturally begin to yellow and die back, drawing energy back into the rhizome for storage. If rhizomes are lifted for winter storage, they are kept cool and dry for two to three months before the start of the next growing season.
Depth and Density: Addressing Crowding and Planting
The physical placement of the rhizome in the soil affects its access to nutrients and its ability to expand and flourish. For optimal growth and flowering, calla lily rhizomes should be planted shallowly, typically two to four inches deep, with the “eyes,” or growing points, facing upward. Planting too deep can delay or prevent the shoots from emerging and establishing properly.
Calla lilies growing in the same container or garden spot for multiple seasons often become severely crowded, leading to a rootbound condition. When the rhizomes are packed too tightly, the plant concentrates its resources on survival and root competition rather than flower production. Dividing and replanting the rhizomes every few years helps to alleviate this crowding, restoring the plant’s vigor and its capacity to produce abundant flowers.