Calla lilies (Zantedeschia) are ornamental plants known for their elegant, trumpet-shaped structures. The vibrant, colored part is not a true flower petal but a modified leaf called a spathe, which wraps around the central spadix. Owners often notice their brilliant white, yellow, pink, or purple spathes unexpectedly shifting back toward a dull green hue. This change is typically a predictable response to biological timing or environmental conditions. Understanding the cause is the first step in maintaining the plant’s desired appearance.
Natural Maturation and Fading
The most frequent reason a calla lily spathe turns green is natural maturation and the end of its blooming cycle. The spathe has a limited lifespan, and as it ages, the specialized pigment cells responsible for the vibrant, non-green colors begin to break down.
The plant starts to reabsorb resources from the dying spathe. This internal breakdown allows the inherent green pigment, chlorophyll, to become dominant and visibly expressed. The spathe shifts its function to a more leaf-like, photosynthetic role before it fully collapses.
This reversion signals that the flower is past its aesthetic peak and is winding down its reproductive phase. The plant focuses its energy on producing seeds or preparing for dormancy. Greening in this context is a normal part of the plant’s life history.
The Role of Light Exposure
The amount of light a calla lily receives significantly influences the color of its spathe. These plants require sufficient light intensity to synthesize and maintain the complex, non-green pigments that give the spathe its characteristic color.
When a plant is placed in a location with insufficient light, it maximizes its ability to capture energy. To compensate for dim conditions, the spathe increases its production of chlorophyll, the green pigment necessary for photosynthesis. This causes the colorful tissue to revert to a leaf-like, green appearance, sacrificing vibrant color for improved energy production.
Conversely, excessively intense, direct sunlight can also negatively affect the spathe’s color. Harsh light causes stress, leading to premature degradation of the specialized color pigments. When these pigments fade quickly, the underlying chlorophyll becomes visible, causing the spathe to green ahead of its normal aging schedule.
Nutrient Imbalances
The composition of the plant’s fertilizer and soil nutrients plays a direct role in regulating spathe color, particularly nitrogen levels. Nitrogen (N) is a primary macronutrient and the main driver of vegetative, leafy growth. This nutrient is a fundamental component of all chlorophyll molecules.
If a calla lily is consistently given a fertilizer high in nitrogen, the plant prioritizes vegetative tissues over colorful spathes. High nitrogen availability encourages the plant to produce more chlorophyll, treating the spathe as another leaf. This chemical signal shifts the tissue’s appearance back to green.
For optimal flowering and color retention, the plant needs a more balanced approach, ensuring adequate amounts of phosphorus (P) and potassium (K). Phosphorus supports flower development, while potassium aids in overall plant health. An imbalance favoring nitrogen can chemically induce the greening phenomenon.
Practical Steps for Color Maintenance
When greening occurs, adjusting the growing environment can help preserve or restore the desired coloration in subsequent blooms. If natural maturation is the cause, the spent, green spathe should be removed through deadheading, which redirects the plant’s energy toward producing new flowers.
If light is the suspected issue, move the plant to a location that receives bright, indirect sunlight. Avoid placing the plant in dim corners or areas that receive intense, unfiltered afternoon sun. Proper lighting ensures the plant has the energy needed to maintain vibrant pigments.
For nutrient-related greening, switch to a fertilizer with a more balanced NPK ratio or one with lower nitrogen content. If the plant has been heavily over-fertilized, flushing the soil with plain water helps leach out excess nitrogen contributing to the color shift.