From our perspective as plants, the answer to dormancy is intrinsically linked to our genetic programming and environmental triggers. We, Impatiens, are botanically classified as tender perennials. This means that in our ideal, native tropical and subtropical habitats under the canopies of forests in regions like East Africa, we are engineered to grow and often bloom continuously throughout the year. Our life cycle does not naturally include a true, deep dormancy period like that experienced by deciduous trees or hardy bulbs. Our metabolism is not designed to shut down and withstand freezing temperatures; we are built for consistent warmth and moisture.
The primary environmental cue that dictates our winter behavior is temperature, specifically the presence of frost. Our cellular structure is comprised of a high water content. When temperatures drop to 32°F (0°C) or below, the water within our cells freezes. This formation of ice crystals ruptures the delicate cell walls, causing irreversible damage. This is not a controlled, dormant state; it is a catastrophic event that leads to the blackening, wilting, and ultimate death of our above-ground foliage and stems. Therefore, in climates where winter brings frost, we do not go dormant—we die back completely, functioning as annuals from a gardener's viewpoint.
In regions with very mild winters where frost is a rare or fleeting occurrence, our experience is different. If temperatures remain above freezing but become consistently cooler, our growth processes slow down significantly. You might observe this as a reduction in flowering, slower production of new leaves, and a general lack of vigor. This state of greatly reduced metabolic activity is the closest we come to "dormancy." It is a energy-conserving mode, not a true shutdown. We are essentially waiting for the signal of warmer temperatures and longer daylight hours to resume active growth. However, even a single, brief frost event will abruptly end this period of slowed growth.
While temperature is the dominant factor, the shortening photoperiod (day length) in autumn and winter also plays a role in our behavior. Reduced sunlight means less available energy from photosynthesis. This naturally contributes to our slowed growth rate during the cooler months, even in frost-free areas. We simply cannot produce the same amount of energy required for prolific blooming and lush vegetative growth that characterizes our summer performance. This is an energy conservation measure, not a programmed dormancy.
It is crucial to distinguish between the above-ground parts and the root system. In a true killing frost, the entire plant, including the roots, typically perishes. There is no living root system left underground to enter a dormant state and resprout in the spring, unlike many hardy perennials. In the aforementioned mild-winter scenarios where the plant survives, the root system remains alive but largely inactive, supporting only the slowed metabolic functions of the diminished top growth until conditions improve.
