Each spring on Long Island, the browning of evergreen foliage after a hard winter produces a wave of concern — and, often, premature action. Gardeners cut back still-living boxwood, rip out rhododendrons that would have recovered, and assume the damage is permanent before the plant has had a chance to show whether the buds are alive.
Winter burn is a physiological injury, not a disease. No pathogen is involved. Understanding what causes it tells you both why prevention works and why patience is the right response in spring.
What causes winter burn
Winter burn results from an imbalance between water loss and water uptake. Evergreen leaves (and needles) continue to lose water through their stomata during winter, especially on warm, sunny, or windy days. When the soil is frozen, roots cannot absorb water to replace what's lost.
Per University of Minnesota Extension, winter burn "is most likely to occur during sunny winter days when temperatures are below 25°F, soils are frozen, and there is little or no snow cover." Wind accelerates water loss significantly.
Per Rutgers NJAES, on Long Island and in the broader Northeast, late February and early March are the highest-risk period — the sun is higher and stronger, temperatures fluctuate, foliage begins to transpire on warm days, and roots remain frozen. Snow cover can actually protect foliage by insulating it from radiation and wind.
Secondary winter injury includes:
Frost cracks — longitudinal splits in bark on the south or southwest side of thin-barked trees, caused by rapid temperature fluctuations.
