Winter presents challenges that threaten plant life, often leading to decline or death. The colder months are a time of intense environmental stress that tests the limits of biological endurance. A plant’s survival depends on its ability to manage two primary threats: the destructive power of freezing water and the profound lack of available moisture. Understanding how plants succumb to winter conditions requires looking closely at the damage inflicted at the cellular level and the physiological struggle to maintain hydration.
Cellular Damage from Ice Formation
The most direct physical harm to plants in winter occurs when temperatures drop low enough for water to freeze within the plant’s tissues. Damage is caused by the formation and expansion of ice crystals, not the cold itself. The less common, and universally lethal, event is intracellular freezing, where ice forms directly inside the plant cells. This rapid crystallization ruptures cell membranes and walls, leading to the irreversible mechanical destruction of the cell’s internal structure.
More frequently, plants experience extracellular freezing, where ice crystals form in the spaces outside the cells. This process draws liquid water out from the cells and into the surrounding intercellular space where the ice is growing. This movement of water is known as freeze-induced dehydration. This osmotic stress concentrates the solutes remaining inside the cell, which helps to lower the freezing point of the remaining fluid. If the temperature continues to drop, the cells become progressively desiccated, collapsing inward as they lose volume.
The speed of the temperature drop significantly influences the type and extent of damage that occurs. A slow, gradual temperature decrease allows the plant to acclimate and facilitates the safer extracellular freezing process. Conversely, a sudden, rapid freeze can trap water inside the cells, promoting the fatal intracellular ice formation. Even if the plant survives the initial freeze, the tissue damage may not be immediately visible, often manifesting later as wilting or browning when the plant attempts to resume active growth in the spring.
The Hidden Danger of Winter Drought
Beyond the direct threat of freezing, winter poses a significant risk of desiccation, a condition often called “winter drought.” This moisture stress is a major killer, especially for plants that retain foliage throughout the year. Plants continue to lose water from their leaves and stems through a process called transpiration, even when the ground is frozen. High winds and low humidity characteristic of winter accelerate this water loss from the plant’s exposed surfaces.
The roots cannot replace this moisture because the water in the soil is locked up in a solid, frozen state. This inability to absorb water, despite its physical presence, is known as physiological drought. When the absorption of water is halted by the frozen soil, the plant’s water loss through transpiration quickly exceeds its uptake. This imbalance rapidly leads to dehydration and tissue damage.
Evergreen plants, including conifers and broadleaf evergreens, are particularly susceptible to this type of damage. Their persistent leaves or needles constantly expose a surface area to the drying winter air, necessitating a continuous water supply. When the soil is frozen for extended periods, the lack of water uptake causes the foliage to dry out. This results in the characteristic brown or “burned” look of winter burn on the needles and leaves.
Survival Strategies: Dormancy and Annual Life Cycles
Not all plants that appear to “die” in winter are victims of cold or drought damage; for some, the decline is a programmed part of their life cycle. Annual plants, such as marigolds and many vegetables, are genetically designed to complete their entire life cycle—from seed germination to seed production—within a single growing season. The individual plant dies completely in the fall after successfully setting seed.
Conversely, perennial plants and trees employ active biological strategies to survive the harsh environmental conditions. They enter a state of dormancy, a period of reduced metabolic activity triggered by shorter daylight hours and cooler temperatures. Deciduous trees shed their leaves in the fall, a process called senescence, which is an effective mechanism to prevent excessive water loss through transpiration during the winter.
During the transition into dormancy, cold-tolerant plants also undergo a process called cold hardening. This involves biochemical changes, such as moving water out of the cells and accumulating dissolved sugars and other solutes within the cells. This increase in solute concentration acts as a form of natural antifreeze, lowering the internal freezing point of the cell contents and limiting the severity of freeze-induced dehydration.