From the perspective of the Calla Lily plant (Zantedeschia spp.), dormancy is not a period of inactivity but a crucial survival strategy. It is a genetically programmed response to environmental cues, primarily decreasing light levels and cooler temperatures. As autumn approaches, the plant senses the shorter days and lower light intensity. This triggers a hormonal shift, notably a reduction in growth-promoting auxins and an increase in inhibitors like abscisic acid. These chemical signals instruct the plant to cease above-ground growth and begin a systematic process of resource reallocation. The primary goal is to conserve energy and protect the vital underground structures—the rhizomes—from the potential stress of winter.
The most visible sign of dormancy onset is the yellowing and withering of the leaves and flowers. This senescence is a deliberate and efficient process. The plant actively breaks down chlorophyll and other valuable compounds in the foliage. Nutrients, particularly carbohydrates and proteins, are translocated from the dying leaves back down into the rhizome. The rhizome serves as a storage organ, a underground larder packed with the energy reserves needed to fuel the next growth cycle. By withdrawing these resources, the plant ensures nothing is wasted. The above-ground parts, having served their purpose, are allowed to die back completely. Attempting to remove green leaves prematurely would be counterproductive from the plant's viewpoint, as it would interrupt this critical nutrient recovery phase.
During dormancy, the rhizome is the entire plant. This modified stem is specially adapted to endure periods of unfavorable conditions. Its thick, fleshy nature allows it to store large amounts of water and starches. It is also equipped with dormant buds, often referred to as "eyes." These buds are meristematic tissue in a state of suspended animation, protected by scale-like leaves. The entire rhizome is encased in a protective skin that helps prevent desiccation and fungal attack. While the plant appears dead above the soil line, the rhizome remains very much alive, albeit at a vastly reduced metabolic rate. Its respiration slows significantly, allowing it to subsist on its stored reserves for the duration of the dormancy period without needing to perform photosynthesis.
The dormancy period is not indefinite; it is broken by a specific set of environmental signals that indicate the return of favorable growing conditions. For the Calla Lily, the key triggers are a combination of a sustained cold period followed by warming temperatures and increased moisture. The chilling period satisfies a physiological requirement that prepares the buds for growth. Once this requirement is met, the arrival of warmer soil temperatures and adequate water (from spring rains or irrigation) signals the plant to resume activity. Hormonal balance shifts again, with growth promoters like gibberellins becoming dominant. This stimulates the dormant buds on the rhizome to swell and begin sending up new shoots, marking the end of the dormancy period and the start of a new growth cycle.
