What is winter burn? Winter burn is a common problem of evergreens including those with broad leaves (e.g., boxwood, holly, rhododendron), needles (e.g., fir, hemlock, pine, spruce, yew) and scale-like leaves (e.g., arborvitae, false cypress, juniper) grown in open, unprotected locations and exposed to severe winter conditions. Evergreen plants that are marginally hardy in a location (i.e., not well-adapted to local winter conditions) are at increased risk for winter burn. Winter burn can be so severe that affected plants may die and/or require replacement.
What does winter burn look like? Winter burn symptoms often become apparent as the snow melts and spring temperatures rise. Foliage starts to brown at the tips of branches with browning progressing inward toward the center of the plant. On broad-leaved evergreens, leaf edges typically brown first, followed by browning of entire leaves. Foliage facing south, southwest or west is most often affected. Symptomatic foliage often begins to drop off starting in spring and continuing through mid-summer as new foliage is produced. In extreme cases, entire plants can brown and die.
What causes winter burn? There are many factors that can contribute to winter burn. In general, plants with shallow or poorly-developed root systems that do not efficiently take up water (e.g., recent transplants) are more prone to winter burn. Warm fall temperatures that delay the onset of plant dormancy can also contribute to winter burn. Similar cold injury can occur mid-winter when temperatures drop sharply at sunset causing foliage that has warmed during the day to rapidly cool and freeze. Foliage under snow or facing away from the sun and direct winds is usually not damaged. Strong winter winds can lead to additional water loss making winter burn more severe. Colder than normal winter temperatures and longer than normal winters can also be factors in the development of winter burn, especially if below normal temperatures occur into April (the time of year when plants normally come out of dormancy and are most susceptible to winter injury). Finally, exposure of plants to salt used to deice roads, driveways and sideways during the winter can make plants more prone to winter burn injury.
How do I save a plant with winter burn? For evergreens such as arborvitaes, boxwoods, junipers and yews, prune out dead, brown, damaged or dying tissue in mid-spring after new foliage is produced. If new foliage has not yet emerged by spring, scratch the bark on affected branches and look for green tissue underneath. If the stem or bud tissue is green, buds on the branch may still break to form new foliage. If the tissue is brown, the branch is most likely dead and you should prune the branch back to a live, lateral bud or branch. Such buds and branches may be far back inside the canopy and pruning may remove a substantial amount of the plant. Pines, spruces and firs typically produce new growth at branch tips in spring that will replace winter burn-damaged needles, and thus pruning may not be required on these evergreens. After a couple of growing seasons, new foliage will fill in the areas that were damaged. If an entire evergreen is brown, recovery is unlikely and the plant should be replaced with something (e.g., a deciduous shrub or tree) that is better-suited to the site.
How do I avoid problems with winter burn in the future? Use a variety of strategies to prevent winter burn before winter arrives. Plant the right plant in the right place. Buy plants that are rated as cold hardy for your location and are well-adapted to local growing and soil conditions. Plants exposed to drying winter sun and winds are more likely to be injured. Therefore, avoid planting winter injury sensitive evergreens, particularly those that require shade or that are marginally cold-hardy, in exposed, sunny, windy areas. Plant them on the northeast or east side of a building or in a protected courtyard. Plant boxwoods, hemlocks, rhododendrons, and yews in partial shade to provide them added protection from winter sun and wind.
Mulch evergreens properly. Apply two inches (on clay soils) to four inches (on sandy soils) of loose mulch (e.g., shredded hardwood, pine, or cedar bark; leaf compost; or wood chips) around the base of evergreens out to at least the drip line (e.g., the edge of where the branches extend). Proper mulch insulates roots from severe fluctuations of soil temperatures and reduces water loss. It also helps protect roots from injury due to heaving that occurs when soils go through cycles of freezing and thawing during the winter.
Water plants properly. Plants that are well-hydrated are less prone to winter burn. In particular, newly planted or young evergreens, especially those planted in open, exposed sites, those planted under eaves, or those planted in dry falls may suffer severe moisture loss during the winter and consequently severe winter burn.
Protect plants during the winter. Use burlap, canvas, snow fencing or other protective materials to create barriers that will protect plants from winter winds and sun. Install four to five foot tall stakes approximately two feet from the drip lines of plants especially on the south and west sides (or any side exposed to wind) and wrap protective materials around the stakes to create “fenced” barriers. Leave the top open. These barriers will deflect the wind and protect plants from direct exposure to the sun. Remove the barrier material promptly in spring.