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Neighbors of DuPage

Understanding and reversing winter damage to evergreens

Urbana – Evergreen plants, which retain their leaves throughout the seasons, are some of the showstoppers of the winter garden, providing some much-needed color in otherwise bleak winter landscapes. Although evergreens do go into dormancy during winter, their foliage is subject to extreme exposure over the winter months, which can result in damage by spring.

“As winter winds constantly strip needles and leaves of water, soil moisture is sometimes in short supply to replace what is lost,” says Ryan Pankau, a University of Illinois Extension horticulture educator.

Some of the limited moisture is due to the fact that soil water is frozen within the soil profile, but it can also result from a lack of precipitation or dry intervals that occur over winter.

“If plants cannot replace lost moisture in needles or leaves, then they will begin to show signs of desiccation in the form of brown, dead foliage,” Pankau says. “In other words, the plant is experiencing drought conditions.”

This type of damage will begin as brown discoloration on needle or leaf tips and may progress as winter continues, to include completely brown or dead foliage on entire limbs. The damage is often limited to the more exposed side of the plant, which is a major clue that winter injury is to blame.

Another cause for winter damage, especially on needle-bearing evergreens, is from road salts. This type of winter injury can look similar to wind exposure, beginning with brown needle tips and progressing to entirely dead branches. It can be the result of salt spray from traffic or the infiltration of salt-laden runoff into the soil profile.

Soil contamination from salt, although rare, is a more extreme condition and may require additional steps to remediate damage to the soil itself. Soil contamination is generally uncommon since most roads drain well and it is not typical for excess water in roadways to heavily inundate landscaped areas.

More commonly, evergreens are damaged from the salt spray generated by traffic near the plants. Similar to wind exposure, this type of damage presents itself on the roadside area of the plant. You can normally identify it from a consistent pattern across many evergreens along the roadway. Most plants will exhibit fairly uniform dead foliage from a similar height downward.

“It is important to realize that plants showing signs of dieback prior to winter, which develop further by spring, are likely experiencing other environmental stresses or pathogens,” Pankau says. “Thorough investigation of the cause of winter dieback is needed prior to treatment.”

Limbs exhibiting winter damage can often be easily pruned out. However, evergreen plants respond differently to pruning based on the growth habit and needs of individual species. Certain evergreen species, such as pine and spruce, lack interior or secondary buds that will be stimulated to grow after the dead tips are pruned off.

“In these cases, I recommend waiting another month or so to be sure any dead-looking limbs are truly gone,” Pankau explains. “Although needles may be entirely dead, there may be live buds on the stem that will produce new growth as the growing season progresses.”

To recognize damage prior to spring leaf-out, there are a few simple tests for identifying live twigs versus dead twigs. Since a twig has very thin bark, it is easily scraped away with your fingernail. “Scrape away a small section of bark and look for green coloring,” Pankau says.

“Green interior bark indicates the twig is still alive. If you see brown or gray, consider that limb a goner. Similarly, individual buds can be removed and carefully bisected to look for green plant parts. If you can find succulent, green plant parts inside the bud, then there is still hope for that limb.”

Although minor instances of winter injury can be pruned out, homeowners should still be concerned about the damage and look for ways to mitigate future winter injury. For highly exposed areas, there are a number of interesting and creative ways to block either wind or salt spray, from makeshift temporary screens to installation of permanent fences.

Consider watering plants well into late fall to be sure soil moisture is adequate going into winter. In addition, a 2 to 4 inch layer of mulch is very effective at conserving moisture and insulating the soil.

In some years, there is just no avoiding extreme winter conditions, but with additional attention during the season and follow-up in spring, your evergreens can flourish for years to come.

Source: Ryan Pankau, Extension Educator - Horticulture and Rosie Ralston