Winter burn: Remember the winter of 2013? That was the last time we had a prolonged series of bone-chilling temperatures and drying winds. There was a lot of winter burn that showed up the next spring. I think it is likely that our more marginally hardy trees such as Japanese maples, redbud and magnolias may have some dieback damage and perhaps reduced bloom on the magnolias. “Winter burn” refers to evergreen foliage browning and dying from the tips inward due to winter damage. Several factors cause winter burn on evergreens, including winter “thaws,” dry soil in fall (which we had in 2017), a long period of very cold temperatures (we’ve sure had this!), 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. Yews can be pruned after the spring flush of growth finishes expanding. You can lightly prune yews in spring before the new growth has expanded to remove winter-killed twigs since new growth will hide the cuts However, prune sparingly, since you don’t know which buds might come back yet. Don’t shear damaged junipers or cut them back to older brown areas because they don’t have latent dormant buds like yews (yews don’t have them very far back on the branches either), and cannot be pruned very far back. Arborvitae can only be pruned in the “green zone” of growing material, not back into the “brown zone” with no growth. It is a bit late for this advice, but for the future, a good way to combat winter burn is to ensure that evergreens go into fall well-hydrated. Water them into early or mid November (if temperatures stay warm enough that the ground is not frozen), providing one inch of water a week if there is no rain (more may be needed in sandier soils). Since conifers don’t go into dormancy as deeply as deciduous trees, a “January thaw,” or direct sunlight on plants (especially on the west or south side of a white building), can cause them to start respiring and giving off water which they can’t replenish via their roots since the ground is frozen. Especially if the foliage and twigs were dry to start with, they desiccate easily. With cold temperatures and wind, there is cold-temperature tissue damage and moisture gets pulled out of the exposed foliage by wind. Another protective measure is to apply 1-3 inches of mulch (more is not better!) evenly around root zone. Don’t pile mulch against the trunks as this can cause damage. Shrubs can be protected with burlap “tents.” Put in stakes around the plant that are slightly taller than the height of the plant and wrap the burlap around the stakes, using heavy-duty staples to attach to wooden stakes or zip-ties to metal stakes. Applying burlap on the top isn’t recommended as it can sag with heavy snow and end up lying directly on branches, which can cause problems.
To learn more about winter burn, visit https://pddc.wisc.edu/ and under the Fact Sheets tab scroll down to “Winter Burn.”