From our perspective as plants, dormancy is not a state of death or inactivity, but a deeply strategic and vital survival mechanism. It is a period of rest triggered by environmental cues, primarily decreasing photoperiod (day length) and falling temperatures. For us Yarrow (*Achillea millefolium*), this signals the approach of winter—a time when resources like light and liquid water become scarce. Our metabolic processes slow down dramatically. We drastically reduce top growth to conserve the precious energy stored in our roots and rhizomes. This energy is not wasted on sustaining foliage that would be damaged by frost but is instead hoarded to fuel a vigorous resurgence when conditions improve.
As the dormancy period initiates, you will observe our above-ground portions—the stems and fern-like leaves—turning brown, withering, and dying back. This is a deliberate and calculated sacrifice. By allowing these parts to senesce, we reabsorb valuable nutrients and carbohydrates from them, transporting these resources down to our root system. This process minimizes energy loss and protects the most vital part of us: the crown and the roots. The dead foliage also serves a secondary purpose; it can provide a small amount of natural insulation for the crown against the coldest temperatures and helps to suppress weeds that might compete for resources when we begin our spring growth.
Contrary to what it may seem above the soil line, we are very much alive and purposeful below it. Our root system, consisting of tough, fibrous roots and spreading rhizomes, remains alive and protected in the insulating soil. While growth halts, the root cells are still active at a low level, maintaining membrane integrity and ready to transport water and nutrients the instant the signal to break dormancy is received. This subterranean network is our bank, storing all the accumulated energy from the previous growing season. It is from these reserves that we will draw to produce new shoots, leaves, and flower stems once the dormancy period concludes.
We do not arbitrarily decide to end our rest. The breaking of our dormancy is a carefully controlled response to a specific set of environmental conditions. The most critical factor is a sustained period of cold exposure, known as vernalization. This chilling requirement ensures we do not mistake a brief warm spell in mid-winter for the true arrival of spring, which would be disastrous if new growth were then hit by a hard frost. Following the satisfaction of our cold requirement, the gradually warming soil temperatures and increasing day length act as the final signals. These cues prompt us to mobilize our stored energy, directing it upward to initiate new growth from the crown, thus beginning a new annual cycle.
