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Every spring gardeners survey how trees and shrubs survived the past winter. Cold winters are often blamed for the majority of plant deaths in Minnesota. As I drive around and see so many white pines with red foliage, I assume it’s winter damage.

According to Janna Beckerman, Extension Plant Pathologist, winter damage is not always the cause. The real culprit in this case is dryness of the fall and winter. This affects needles throughout the entire tree, causing desiccation. This developed when warm air temperatures tricked the tree into becoming active. As a result, the tree loses water by transpiration. Unfortunately, the roots are still frozen and water cannot get through the foliage to replace the lost moisture. This causes the needles to dry. As the needles dry, they turn reddish-brown in the early spring.

Most plants will show symptoms evenly throughout the tree. Plants exposed to extreme temperature fluctuations or strong winds, or direct sun from the south or west facing sides are more severely affected. This results in a pattern where one side is more severely affected than the other. Evergreens in windbreaks, with southern or eastern exposure, regularly have winter injury every year. In some cases, groups of trees without an obvious exposure show symptoms. These trees are probably stressed already by previous problems, and are unable to tolerate even minor stress. Trees planted too deeply, too close together, or in poorly draining soils are all susceptible to developing winter injury.

Although this year appears particularly bad to Eastern White pine, white-cedar, junipers, yew and rhododendron are also commonly affected. Non-native conifers, like Alberta spruce, regularly suffer from winter damage.

It is important to note that winter injury can be misdiagnosed as salt injury. Susceptible plants growing beside high-traffic roads and sidewalks develop injury from de-icing salts when passing cars spray and aerosolize road salt.

The damage that is seen occurs when the salt that lands on needles is absorbed by the plant. When it accumulates to toxic levels, the needle tips are killed. White and red pines are very susceptible to salt spray damage. Scots pine, Norway spruce, juniper and eastern red cedar are moderately susceptible. Austrian pine, larch and black spruce are tolerant to salt spray damage

In addition to directly damaging the needles, salty run-off can directly burn or be absorbed by the roots. The accumulation of toxic levels of sodium can result in burning and browning symptoms on the needles. High concentrations of salts in the soil can alter nutrient availability, modify pH, and produce Pythium root rot conditions. Unfortunately, for the plant that is already turning red, there is little that can be done at this point.

However, there are some things you can do in the future:

•Water all plants thoroughly every fall, with special attention to conifers, to minimize winter drought stress.

•Mulch if it is possible. Mulching insulates the soil, maintains moisture, and allows roots to replace water lost by the foliage. It also insulates against deep frost.

•Plant salt tolerant plants in areas where de-icing salt may be used. Most conifers do not tolerate salt well. Some salt tolerant trees are mentioned earlier in this article.

•Plant susceptible conifers in sheltered sites which are not exposed to full sun, salt damage, or prevailing winter winds.

•Do not apply nitrogen fertilizer late in the growing season. Nitrogen promotes immature growth and prevents this growth from becoming dormant. Such growth is very susceptible to frost injury. Do fertilize in early spring to stimulate growth and replace any growth lost due to winter injury.

Contrary to their terrible appearance, affected trees and their buds are not dead. Don’t prune them or remove discolored trees until plants have had the opportunity to show if they recovered. Minnesota conifers are well adapted to long, severe winters and have the ability to survive winter injury. It is likely your trees are alive, and will survive even if they have turned red.

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Ways to access

information

www.extension.umn.edu/county/chisago Check out the “Hot Topics” box in the middle of the page for current Chisago County Master Gardener news and events.

You can also click on “Ask a Master Gardener” next to the cute little flower on the right hand side of the page. Here you can search 1000s of answers from Master Gardeners around the state. If you don’t find your answer, you can submit a question online or search for University publications, Bell Museum of Natural History. For information about snakes, skunks, raccoons or other wildlife around your yard, call the wildlife information line at (612) 624-1374 or www.bellmuseum.org.

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