It is a common sight that puzzles many calla lily owners: the vibrant color of their bloom often fades, replaced by a distinct green hue. This change occurs because the colorful, trumpet-shaped part is not a true flower petal, but a modified leaf called a spathe. The spathe wraps around the central spike, or spadix, which holds the tiny, actual flowers. The greening of the spathe is a widespread and usually harmless part of the plant’s natural life cycle.
When Green is Normal: The Life Cycle of the Spathe
The most frequent reason for a calla lily spathe to turn green is natural aging, a process known as senescence. Since the spathe is genetically a leaf structure, it retains the ability to revert to its leaf-like function. The vibrant, non-green colors are due to pigments like anthocyanins and carotenoids that mask the green chlorophyll.
As the bloom matures and the true flowers on the spadix are pollinated, the plant shifts its energy away from the display structure. The spathe’s cells start to synthesize chlorophyll again, a process called regreening, to recover energy. This allows the spathe to continue photosynthesizing, converting the spent bloom into a working leaf that supports the plant’s overall health and seed development.
This greening is an expected part of the spathe’s lifespan. Once the color has fully reverted to green, the bloom’s purpose of attracting pollinators is complete. Removing the greening spathe by cutting the stem near the base—a process called deadheading—will encourage the plant to direct energy toward producing new blooms instead of seeds. This simple action helps maintain the plant’s aesthetic appeal while promoting the next flowering cycle.
The Role of Light and Nutrients in Color Change
While natural aging is the primary cause, environmental conditions can hasten or intensify the greening process. Imbalances in light and fertilizer management particularly affect the spathe’s pigmentation.
Light Exposure
If a calla lily is exposed to intense, direct midday sunlight, the plant can become stressed, prompting a protective response. The spathe may increase its chlorophyll production prematurely to shield itself from potential damage. This excess chlorophyll causes the non-green color to be overwhelmed, resulting in a rapid shift to green. Placing the plant in an area with low light can also lead to a greenish tint, as the plant attempts to maximize light absorption by producing more chlorophyll.
Nitrogen Levels
Fertilizer composition significantly influences the coloration of the spathe. Nitrogen is a macronutrient that promotes lush, green vegetative growth in leaves and stems. If the plant receives a fertilizer with a high nitrogen ratio, it encourages the spathe to revert to its green state. This imbalance causes the plant to prioritize green growth over maintaining energy-intensive colored pigments. For optimal flowering, calla lilies benefit from a fertilizer lower in nitrogen and higher in phosphorus and potassium during the blooming stage.
Adjusting Care for Future Blooms
To ensure the next flush of blooms maintains its intended color for the longest duration, adjust the plant’s care regimen. The goal is to reduce environmental stress and provide the correct nutritional support during the flowering period.
Light adjustment is the most immediate step, involving relocating the plant to a spot that receives bright, filtered light, avoiding harsh afternoon sun. For indoor plants, this means placing them near a south-facing window shielded by a sheer curtain or moving them back from the direct light source. This moderate light level is sufficient for photosynthesis without triggering the spathe’s protective regreening response.
Correcting the nutrient profile is also important for color retention. During the active growing and flowering season, switch to a fertilizer with a higher middle and last number in the N-P-K ratio, such as a 5-10-10 formula. This provides the phosphorus and potassium needed for flower development and color expression while limiting the nitrogen that encourages green growth.
Maintaining consistent, moderate temperatures is a final preventative measure. Calla lilies prefer an environment between 60 and 80 degrees Fahrenheit. Temperature fluctuations, particularly heat stress, can prematurely signal the spathe to senesce and turn green. Stable conditions reduce the need for the plant to deploy stress responses that affect bloom color.