Protect your shrubs from the extreme cold

David Hillock, Oklahoma State University Cooperative Extension consumer horticulturist, said although many trees, shrubs and perennials go dormant for the winter, fluctuating temperatures, intense sun, low soil moisture and dry, windy conditions can be quite hard on shrubs. This is particularly true for evergreens, which remain active during the winter months and often sustain cold damage.

“The first step in protecting plants from winter damage is to properly irrigate before the first hard freeze.  While it is a good idea to hold back on water during autumn to allow plants to harden-off for winter, it is essential for shrubs to enter winter with adequate soil moisture,” Hillock said. “After a few light frosts in fall, irrigate shrubs deeply and apply a layer of mulch to regulate soil moisture and temperature.” 

Broadleaf and needled evergreen shrubs will require occasional irrigation throughout the winter. These plants continue to lose water through transpiration, especially during dry, windy periods when sunlight is intense. When plants lose water faster than the roots can replenish it, the plant becomes desiccated. 

Signs of desiccation in broadleaf evergreens, such as camellia and rhododendron, include yellow or orange discoloration of foliage. Needled evergreens display brown or rusty-colored needles. In severe cases, entire branches can desiccate and die. Regular irrigation ensures moisture is available during critical times, especially when soils are cold and water is less available. 

“Despite our best efforts to select climate-appropriate plant material for our gardens, unexpected weather events will inevitably occur,” he said. “When the weatherman warns of unusually cold temperatures, take the time to protect the shrubs in your landscape. Remember, they are an investment and contribute to the overall value, as well as beauty, of your home.”

Watering plants several hours before a freeze is the first defense against damage. During a temporary cold snap, cover entire shrubs with burlap, sheets or blankets to insulate plants. For the best protection, use a frame to prevent the covering from touching the plants. Extend the cover all the way to the ground to help retain heat radiating from the soil.

Damage is normally worst on the side of the plant facing the wind or sun. Intense winter sun can cause scorching on the south- and west-facing sides of the shrub. When planting new shrubs, place sensitive species in locations sheltered from prevailing winds and direct winter sun. This includes the north, northeast and east sides of buildings, structures or windbreaks. For existing shrubs in exposed locations, a simple barrier can be used to protect plants. Stretch canvas or burlap between posts along the south and west sides of the shrub. Attach the material securely and extend from ground level to the full height of the shrub. 

“While we can’t entirely eliminate winter damage, gardeners can certainly take steps to reduce and prevent problems in the landscape. Though much of the landscape may look dormant, remember many plants are still actively using water,” Hillock said. “Keep an eye on the weather and be mindful of accumulated precipitation each month. When cold weather strikes, consider taking extra steps to protect the most sensitive plants in your garden.”

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Trisha Gedon
Communications Specialist
Agricultural Communications Services
Oklahoma State University
136 Agriculture North
Stillwater, OK  74078
405-744-3625 (phone)
405-744-5739 (fax)
[email protected]