Dealing with winterkill in evergreens

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Catherine W. Idzerda
Sunday, March 30, 2014

JANESVILLE—Evergreen or ever brown or just plain dead?

That's the question many homeowners are asking themselves about the evergreens in their landscape.

An usually long and cold winter has lead to what experts refer to as “winter kill” of evergreens.

We asked experts from the UW Extension to explain what happened to the evergreens and if anything can be done to fix them.

Q: What's wrong with my evergreen?

A: It's called simply “winter kill,” and refers to the death of parts of evergreen foliage. Brown spots or tip dieback are the most common symptoms.

“It's caused by a combination of several things,” said Mike Maddox, certified arborist and state director of the Master Gardener Program.

On a sunny day, the needles “perspire”—they loose moisture, Maddox explained.

When the ground is frozen so deeply, the plant cannot take up water through its roots to replace the perspired moisture.

It doesn't help that many landscape evergreens are planted in “micro climates” that can exacerbate the situation.

For example, yews planted up against the house will be subject to the reflection of the sun against the house, increasing the warming effect.

Q: How bad has this winter been?

A: Maddox said we've had so many mild winters that this one just seems abnormally bad.

However, the numbers show that it has been an usually bad one. The Janesville area has experienced a near-record number of snowfalls. In addition, the average median temperature for the winter of 2013-14 was the lowest since 1948.

Q: So it was just the cold?

A: No, salt damage could be causing some of the problem, too, Maddox said.

With this year's near record number of snowfalls, salt from sidewalks and streets will be a significant factor in winter burn.

Q: What species was hit the hardest?

A: “It seems like yews have been hit the hardest,” said Maddox. “I've seen a lot of those green meat balls—yews—in front of houses with brown spots.”

Yew, arborvitae and hemlock are most susceptible, according to UW Extension, but winterkill can impact all evergreens, especially new transplants.

Q: Will our plants recover? And what can we do to avoid winterkill in the future?

A: Recovery depends on the extent of the damage, Maddox said.

Wait until later in the spring before doing any pruning, Maddox said. It's possible that parts of a tree or shrub that look dead might still have surviving buds. Those might green up and fill in the brown areas.

Prune back the dead parts of the plant if they don't green up.

However, it isn't always easy to prune an evergreen into an acceptable shape, and you might want to replace the plant and start over, Maddox said.

When planting, try to pick a variety resistant to winter kill, extension specialists say. Talk to the specialists at your local nursery.

Avoid planting evergreens where they will be subject to long periods of warm afternoon sun on winter days.

When the sun goes down, “the plant my suddenly be plunged into sub-zero cold, resulting in damage,” according to the University of Minnesota Extension.

Anti-desiccant and anti-transpirant sprays are sometimes recommended to prevent winter burn. However, most studies show that such treatments don't work, according to the UW Extension.

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