Protect Evergreens From Winter Blasts

First posted on 11-12-2010

Winter can be tough on landscape plants, especially evergreens.

Needle-leafed plants can suffer serious winter injury from cold, dry winter winds, said a University of Missouri Extension horticulturist. Newly planted evergreens are at greatest risk.

“There are a few things you can do to help evergreens endure those wintry blasts,” said Chris Starbuck.

Evergreen plants lose water to the atmosphere from its leaves throughout winter through a process called transpiration, he said.

This is not a problem if the roots can take up enough water from the soil to replace what the tree has lost to transpiration. However, if the soil is dry or the stems frozen, water loss can exceed uptake, leading to drying or desiccation of the foliage.

Desiccation is not obvious because the needles of evergreens may be rigid and resistant to wilt. The first signs may be browning of the leaf tips. Because cold air holds very little moisture, strong winds during a cold period can speed up the desiccation of evergreen foliage.

“The first line of defense is good planting technique,” Starbuck said. Evergreens need well-drained, slightly acidic soil to thrive. A raised bed or berm amended with organic matter and adjusted to a pH below 6.0 will get root growth off to a good start.

“Perhaps the most important practice in preventing winter injury is to make sure that the soil is moist as winter approaches. If the fall is dry, a thorough watering in November is good insurance,” he said.

Make sure that soil drainage is sufficient so that the water won’t collect around the roots for more than a few hours during wet periods in winter and spring.

“The quickest way to kill an evergreen is to drown it,” he said. However, some watering during warm, dry spells in winter and early spring can be helpful, particularly for newly planted evergreens with limited root systems.

Mulching is also important because it conserves soil moisture and keeps the soil from freezing deeply, so more water is available.

Delaying mulching until the soil surface begins to freeze can help move the plant into faster dormancy, reducing the risk of winter injury.

Wind protection can reduce desiccation injury for evergreens planted within the previous two years. A simple screen made with burlap strung between fence posts can be very effective in protecting broadleaf evergreens from the north and west winds.

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