‘Winter burn’ is a type of damage to evergreen foliage that occurs over winter or in early spring. Symptoms include browning and dying from foliage tips, extending inward. Several factors cause winter burn, including winter ‘thaws’ where the temperatures rise above freezing for a long period of time such that the plants come out of dormancy and start to transpire water, dry soil in fall, long periods of very cold temperatures, winter sun/wind exposure, poor siting of susceptible plants, recent planting/transplanting, and the individual plant’s susceptibility. Commonly affected plants include yews, junipers, boxwood, arborvitae, rhododendrons, dwarf Alberta spruce and hemlock. Some plants may recover as new growth emerges, but many do not.
One good way to combat winter burn is to ensure that evergreens go into fall well-hydrated. Provide one inch of water a week if there is no rain (more may be needed in sandier soils or with newly planted/transplanted evergreens) into early or mid-November (if temperatures are warm) in the southern/central part of the state. The cut-off time for watering will be earlier farther north. Also, don’t plant evergreens in fall. They generally don’t get their roots established well enough and become very susceptible to winter burn damage.
Conifers don’t go into dormancy as deeply as deciduous trees that lose their leaves. Hence, a rise in winter air temperatures (a ‘January thaw’) or even direct sunlight on plants that raises foliar temperatures above freezing can cause them to come out of dormancy briefly or for longer periods. Coming out of dormancy causes the foliage to start transpiring and giving off water, which can’t be replenished via the roots since the ground is frozen. Especially if foliage and twigs were dry to start with due to dry fall weather, they are prone to desiccation. This phenomenon is very common on the west and south sides of buildings, where there is a lot of sunlight and reflected heat off buildings, so planting evergreens there is not recommended. Besides watering, a protective strategy is to apply 1-3” of mulch (more is not better!) evenly around root zone to keep moisture in during the growing season. Don’t pile mulch against trunks as this can cause damage.
Shrubs can also be protected with burlap ‘tents’. Put in stakes few inches taller the height of the plant around its circumference, wrap burlap around the stakes and secure it. Avoid burlap on top, as it can sag with heavy snow and end up lying directly on branches.
Research indicates products sold as anti-desiccants/anti-transpirants are not reliable because they tend to flake off too soon to protect plants effectively, or, conversely, residual product stays on too long into the growing season and interferes foliage respiration. A fact sheet on the causes of and solutions for winter burn is available at the Wisconsin Horticulture website, https://hort.extension.wisc.edu/ under Evergreen Diseases and Disorders – look for ‘Winter Burn’ as the title.
