The dormancy cycle of Paeonia lactiflora is a complex and vital physiological process that ensures the plant's survival through adverse conditions and its successful regeneration and flowering in subsequent growing seasons. From the plant's perspective, this cycle is not a period of simple rest but one of intense, internal preparation and environmental sensing.
As autumn progresses, the plant perceives critical environmental cues: shortening photoperiod (day length) and, more significantly, declining temperatures. From the peony's viewpoint, these signals are an unmistakable warning of the impending winter. In response, growth inhibitors, primarily the plant hormone abscisic acid (ABA), accumulate within the terminal buds on the crown's eyes and the root system. ABA actively halts cell division and metabolic processes, forcing the plant into a state of endo-dormancy. This is an internal, physiological block to growth that prevents the buds from sprouting prematurely during an unseasonably warm spell in mid-winter, which would be fatal to the new growth.
To break this self-imposed endo-dormancy, the plant has a non-negotiable requirement: exposure to a sustained period of cold temperatures, typically between 0°C and 10°C (32°F and 50°F). This is known as the chilling requirement. From the plant's biochemical perspective, the prolonged cold gradually degrades the accumulated ABA (the growth inhibitor) while simultaneously promoting the synthesis and mobilization of growth-promoting hormones like gibberellins and cytokinins. The plant is essentially using the cold as a timer; only after experiencing a sufficient quantity of "chilling hours" does it perceive that winter has been long enough and it is safe to prepare for spring. Without meeting this requirement, the plant will either fail to emerge or will exhibit stunted, erratic growth.
Once the chilling requirement is satisfied, the internal biochemical block to growth is removed. The plant enters a state of eco-dormancy, where growth is now solely inhibited by external, environmental factors—namely, the soil temperature being too cold for root function and shoot expansion. The plant is poised and waiting. Its meristems are primed, and hormone ratios have shifted in favor of growth. When the soil warms to a sufficient level in spring, the plant interprets this as the final all-clear signal. Stored carbohydrates in the thickened roots are mobilized, providing the energy for the rapid elongation of shoots from the buds, the expansion of new leaves, and ultimately, the development of flowering stalks.
After flowering, the plant's perspective shifts to energy acquisition and storage. Through photosynthesis, the leaves produce carbohydrates that are not only used for immediate needs but are also transported down to the roots for storage. This energy reserve is absolutely critical for surviving the next dormancy and fueling the initial growth burst the following spring. As autumn returns, the cycle begins anew. The plant senses the familiar cues, and the process of shutting down growth and re-entering a state of dormancy recommences, ensuring its perennial nature.
