The relationship between wind, cold temperatures, and plant health is a common concern for gardeners. While plants do not experience “wind chill” in the same way that warm-blooded animals do, the movement of air significantly influences their temperature and hydration status. Understanding the physical mechanisms by which wind interacts with plant surfaces is necessary to protect vulnerable species from winter injury.
Clarifying the Terminology
The official wind chill calculation determines how quickly an object generating its own heat loses warmth to the surrounding air and is based on a human model. Because plants do not metabolically produce heat, they are not affected by the wind chill temperature rating. Plant tissues generally equilibrate to the actual ambient air temperature. If the air temperature is 35°F, a plant will react to 35°F, regardless of a lower wind chill reading.
The real impact of wind involves disrupting the boundary layer, which is a thin, insulating layer of relatively still, humid air surrounding every leaf. This boundary layer acts like a blanket, slowing the rate at which water vapor escapes the leaf surface. When wind speeds increase, this layer is thinned or removed entirely, which directly increases the rate of gas and energy exchange.
Primary Mechanisms of Wind Damage
The most significant non-temperature-related damage caused by wind is desiccation, or excessive drying, which results from the acceleration of transpiration. Transpiration is the process where water vapor exits the plant through tiny pores, called stomata. By removing the humid boundary layer, wind creates a steeper concentration gradient between the moisture inside the leaf and the drier air outside, causing water vapor to be pulled away more rapidly.
This increased water loss is particularly damaging to evergreen plants in winter, leading to physiological drought. When the ground is frozen, roots cannot absorb moisture to replace what is lost through the leaves. This deficit results in the browning or “winter burn” often seen on broadleaf evergreens like hollies and boxwoods.
Beyond water loss, strong wind causes mechanical stress that physically injures plants. High-velocity air can tear leaves, break branches, and cause the entire plant to rock back and forth in the soil, known as “wind-rock.” This rocking action stresses and breaks delicate feeder roots, creating entry points for soil-borne pathogens and compromising the plant’s ability to take up water.
How Airflow Exacerbates Freezing Injury
While wind does not change the air temperature, it significantly influences the speed at which plant tissue temperature drops to the ambient level. Moving air, via forced convection, prevents the plant from maintaining any localized heat or moisture buffers. This rapid cooling increases the risk of damage, especially in plant parts that are not fully cold-hardened.
The rate of cooling is particularly important because rapid temperature decreases can lead to more destructive intracellular freezing. When cooling occurs slowly, water within the plant cells has time to move out and freeze in the extracellular spaces, a less damaging process. Rapid cooling, however, can trap water inside the cell, causing ice crystals to rupture the cell membrane, leading to cell death and tissue necrosis.
This wind-assisted rapid cooling can manifest as a specific type of injury, especially on the side of the plant facing the prevailing wind. The physical force of the wind also removes the accumulated moisture that might otherwise slightly buffer the leaf surface temperature. This combined effect of forced convection and desiccation makes cold wind a serious threat to exposed plant tissues and buds.
Protecting Vulnerable Plants
Gardeners can take several proactive steps to minimize damage caused by cold, moving air. Establishing physical barriers is an effective strategy to reduce wind speed around sensitive plants. Temporary structures like burlap screens or woven fencing placed on the windward side of evergreens can significantly mitigate airflow velocity.
Adequate hydration, especially before the ground freezes, helps plants resist wind-related damage. Well-watered cells are more resistant to both desiccation and freezing injury, making it important to keep the soil damp through the autumn. Watering during dry winter spells, when the temperature is above freezing, can help broadleaf evergreens replenish lost moisture.
Thoughtful placement and plant selection offer long-term protection. Placing tender or vulnerable plants in locations sheltered by buildings or hedges—which act as permanent windbreaks—can shield them from the harshest winter gusts. Choosing plant varieties specifically rated for the local climate’s cold and wind exposure will also reduce the likelihood of injury.