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Watch out for winter burn

An evergreen bush with a brown spot
Look for winter burn as spring arrives.
February 19, 2016

As spring arrives, you may start to notice brown patches on some evergreen shrubs. They’re likely to become more noticeable against the green of the garden as leaves open on other plants.

These brown patches of foliage are called winter burn, according to Doris Taylor, Plant Clinic manager at The Morton Arboretum. They are leaves or needles that have dried out and died over the winter.

This can happen either because the evergreen plants did not have enough water in their leaf tissue and root systems or because their roots could not absorb water from frozen soil, she says. Cold winds, spray from road salt, and runoff from salt used to melt snow on walks also can dry out leaf tissue.

Warm spells in late winter can make the problem worse. Warmth and sunlight trigger the leaves to start photosynthesis, which uses up water. But if the ground still is frozen, the plants’ roots can’t absorb water to replenish the supply in plant tissues. The result: Without water, leaves or needles turn yellow and then brown.

Broad-leafed evergreen such as boxwoods, hollies, and rhododendrons often show the most damage because they have more exposed leaf area than evergreens with thin needles.

Winter kill is most severe in harsh winters, Taylor says. This winter has been moderate, but some evergreens still are likely to show damage.

Once the soil begins to thaw, you can help damaged shrubs recover by watering them well, Taylor says. But don’t apply fertilizer unless a soil test shows you actually need it. Most soils in northern Illinois have all the nutrients shrubs need.

If you prune out branches with dead foliage, the shrub will likely fill in the gap with new growth, Taylor says. 

But “don’t rush to prune out branches that may not really be dead,” she says. “On many of the samples people bring in to the Plant Clinic, the leaves are discolored but the buds are still alive. That means the branch is still alive too.”

Once the ground thaws and the shrub can absorb water through its roots, it may recover.

One way to tell whether a branch alive is to take your thumbnail and gently scratch a small nick in the bark. If you see a green layer beneath the outer bark, the branch still is alive. If its leaves or needles have dried out, it can still sprout more.

A live branch may have suffered winter burn, but not winter kill.