The sudden appearance of brown needles or leaves on otherwise healthy evergreen plants during or after winter can be alarming. This discoloration often raises the question of whether the plant is experiencing a normal seasonal shift or a serious injury. Browning is usually caused by a combination of natural physiological changes and environmental stress. This article explains the difference between natural color change and actual damage, details the mechanism behind winter injury, and outlines steps to protect your plants.
Natural Winter Bronzing vs. True Damage
Some evergreens naturally change color in colder temperatures, a process known as winter bronzing. This discoloration is a harmless, adaptive response where the foliage develops reddish, purplish, or bronze pigments. These pigments, such as anthocyanins, act like a natural sunscreen, shielding the chlorophyll from intense winter sunlight. Species like certain cultivars of Arborvitae (Thuja), Junipers, and Boxwood commonly exhibit this temporary color shift. The color change signals dormancy and reverses completely when temperatures warm up in the spring. In contrast, true winter damage, often called winter burn or desiccation, results in a widespread, permanent tan or brown color that indicates dead tissue.
The Mechanism: Why Evergreens Lose Moisture in Winter
The primary cause of widespread browning is winter desiccation, which is the plant drying out. Evergreens retain their foliage year-round, meaning they continue to lose water through transpiration, even in winter. This water loss is accelerated by dry winter winds and intense, direct sunlight, which warms the foliage and drives off moisture. This moisture loss becomes damaging when the ground is frozen, creating a physiological drought. Roots cannot absorb water from frozen soil to replace what is lost through the foliage. The resulting moisture deficit causes the needles to dry out, turn brown, and die from the tips inward, often appearing on the sides exposed to prevailing winds or afternoon sun in late winter and early spring.
Assessing the Severity of Brown Needles
Determining the severity of browning requires a simple inspection of the affected branches. If browning is limited to the oldest needles deep inside the canopy near the trunk, it is likely a normal, annual shedding process. True desiccation injury typically affects the younger, outer needles and branch tips, often occurring on the windward or sun-exposed sides of the plant. To check if a branch is still alive, perform a scratch test by gently scraping the outer bark of a small, affected twig. If the tissue immediately underneath is bright green, the branch is still viable and may recover. If the scraped tissue is brown and dry, the branch is dead and will not produce new foliage.
Protecting Evergreens from Winter Injury
The most effective preventative measure is ensuring the plant is fully hydrated before the ground freezes solid. Deep, thorough watering in late fall provides a critical reservoir of moisture for the roots throughout the winter. Continue this winter watering during extended dry spells when the temperature is above freezing, around 40 to 45 degrees Fahrenheit.
Physical Barriers
Physical barriers offer excellent protection for vulnerable plants, especially those newly planted or exposed to harsh conditions. Placing a screen or windbreak made of burlap on the south and west sides of the evergreen can deflect drying winds and intense solar radiation.
Anti-Desiccant Sprays
Anti-desiccant sprays, applied to the foliage in late fall, create a thin, waxy coating that reduces the rate of water loss by about 15 to 20 percent. These sprays must be applied when the plant is dormant and temperatures are between 40 and 50 degrees Fahrenheit, ensuring the coating has time to dry before freezing weather or rain.