Roses, like many deciduous plants, enter a natural phase of suspended growth known as dormancy, which is necessary for their long-term health and survival. This winter rest allows the plant to conserve energy, protect tissues from freezing, and accumulate resources for robust growth and flowering in the spring. Recognizing this transition is fundamental to proper rose care. Dormancy is triggered by a combination of environmental signals that gradually communicate that winter is approaching.
Identifying the Temperature Trigger
The primary cue signaling dormancy is a sustained drop in ambient temperature. Roses typically begin this process when temperatures consistently fall below 40 to 45 degrees Fahrenheit (4 to 7 degrees Celsius). Dormancy is induced not by a single, sharp frost, but by a prolonged period of chilling temperatures that signal the arrival of winter.
This gradual temperature reduction slows the plant’s metabolic rate, initiating the shift to rest. Applying protection too early can confuse the plant, causing it to continue growing and making it vulnerable to hard freezes. Decreasing daylight hours, known as photoperiodism, also influence the plant’s timing. Shorter days serve as a reliable signal that the growing season is ending, synchronizing the plant’s changes with the coming cold.
The Biological Necessity of Dormancy
Dormancy is a survival strategy where the rose systematically shuts down active processes to withstand harsh winter conditions. During this phase, the plant’s cells transform to protect themselves from freezing damage. The water within the cells is chemically altered to resist freezing, and cell walls thicken, which hardens the tissues and increases cold tolerance.
The plant reallocates its energy stores, moving starches and sugars from the leaves and upper canes down into the roots and crown. Shedding leaves reduces water loss and eliminates tissue susceptible to winter damage. This period of reduced activity allows the rose to repair damage and build up an energy reserve. The stored nutrients fuel the burst of new growth and flowering when warmer temperatures return in the spring.
Preparing Roses for Winter Rest
To assist the rose in its natural transition into dormancy, a gardener should adjust care practices starting in late summer or early fall. Ceasing all fertilization approximately six weeks before the expected first frost is a primary step, as new growth stimulated by fertilizer will not have time to mature and will be easily damaged by cold. Water should continue to be supplied until the ground freezes, ensuring the roots remain hydrated to withstand the drying effects of winter air.
It is beneficial to stop deadheading spent blooms at this time, allowing the plant to form rose hips. This is a visual cue that helps signal the end of the reproductive cycle and promotes the onset of dormancy. Once the rose has experienced several days of below-freezing temperatures and its leaves have dropped, physical winter protection can be applied.
This often involves hilling, where a mound of soil, compost, or shredded leaves is placed around the base of the plant, covering the sensitive graft union to a depth of 8 to 12 inches. This protective layer is not meant to keep the rose warm, but rather to keep the crown consistently cold, preventing damaging freeze-thaw cycles that can weaken the plant.