Protect evergreen shrubs from winter burn: “Winter burn” refers to a type of damage to evergreen foliage that occurs over winter. Typical symptoms are browning and dying from the tips of the foliage inward. Several factors cause winter burn on evergreens, including winter thaws, dry soil in fall (which we had at some points in 2017), a long period of very cold temperatures, winter sun/wind, 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.
You may recall that the winter of 2013 caused a lot of winter burn on a number of species to due long periods of excessive cold accompanied by sweeping winds. 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) into early or mid-November (if temperatures stay warm) in the southern/central part of the state. Conifers don’t go into dormancy as deeply as do deciduous trees that lose their leaves. Hence, a rise in winter temperatures (a “January thaw”) or just direct sunlight on plants raising foliar and air temperatures above freezing can cause them to come out of dormancy, at least for a brief time. This phenomenon is especially common on the west or south side of a white building. Coming out of dormancy can cause the foliage to start respiring and giving off water, which it is unable to replenish via roots since the ground is frozen. Especially if the foliage and twigs were dry to start with, due to dry fall weather, they desiccate. Planting evergreens close to the south or west side of buildings, due to this problem is not recommended.
A protective measure is to apply 1-3 inches of mulch (more is not better!) evenly around root zone to keep the moisture in. Do not pile mulch against the trunks as this can cause damage. Shrubs can also be protected with burlap “tents.” Put in stakes around the plant that are a few inches taller the height of the plant and wrap the burlap around the stakes. Applying burlap on the top is not usually recommended as it can sag with heavy snow and end up lying directly on branches, which can cause problems. There are some products sold as “anti-dessicants” or “anti’transpirants.” Research indicates that these are not reliable because they tend to flake off too soon to protect the plants effectively, or, that conversely, the product actually stays on too long into the growing season and interferes with the ability of the foliage to “breathe.” A fact sheet on the causes of and solutions for winter burn is available at the Plant Disease Diagnostic Clinic website, https://pddc.wisc.edu/ under the “Fact sheets” tab.