Mild winters not so nice for some plants

By Marianne Ophardt, Special to the Tri-City Herald January 20, 2012 

KENNEWICK -- This week's snow storms are a reminder that it really is winter!

Up until now, our winter had been very nice, with little rain, snow or ice.

Gardeners were hoping an early spring was right around the corner. However, record-breaking warm winter temperatures and little precipitation up until this week mean that trees and shrubs might have suffered stress from winter drought.

Evergreens that keep their green leaves through the winter lose moisture through those leaves. This includes needled evergreens such as arborvitae, pine, spruce and fir, and broadleaf evergreens such as rhododendrons, boxwood and laurel. If there isn't enough moisture in the soil to replenish what is lost through their green leaves, the plants will suffer from drought stress and winter burn.

Evergreens aren't the only trees and shrubs that can suffer from winter drought stress. Shallow-rooted deciduous plants also may be injured when their roots become desiccated in the dry soil. Particularly prone to winter drought are birch, silver maple, Norway maple, hybrid maples, linden and dogwood.

During mild winter weather, gardeners should check the soil moisture (using a trowel or shovel) in their landscapes and water vulnerable plants if the soil is dry. When the soil is dry, it means the laborious task of dragging out and providing trees and shrubs with a good soaking is needed. Plants situated beneath eaves, where they don't receive natural precipitation, and trees and shrubs planted within the past two years are especially susceptible to winter drought damage. Water should not be applied if the soil is frozen.

Because of the very mild early winter weather, the buds of many trees and shrubs seem about ready to pop open. That's worrisome, but there is not much that can be done about it. Record high winter temperatures have led plants to deacclimate, losing part of their winter hardiness and leading buds to swell as if spring is near. The best we can do is hope for cold weather but no severely cold temperatures. Buds will become more vulnerable to cold damage if temperatures remain higher than normal for any length of time, especially as the days grow longer.

The weather this week might be a clue that the National Oceanic and Atmospheric Administration's seasonal outlook for January, February and March is accurate. Their information indicates that there are "elevated chances for below normal temperatures for the northwest parts of the great basin and the Pacific Northwest" and "enhanced chances for above median precipitation for the parts of the Pacific Northwest." I could do without the snow, but if we don't get more snow in the Cascades, we will be looking at a growing season with limited water for irrigation.

Another result of the recent warm weather was overanxious gardeners who wanted to get started with their early spring gardening chores. Now that we have been reminded that winter is still here, eager gardeners might want to consider becoming a Master Gardener volunteer.

Training to become a Washington State University Extension Master Gardener starts Tuesday and continues for 16 weeks. In return for the quality training they receive, volunteers agree to 50 hours of service to the public, helping answer other people's gardening questions and maintaining the Master Gardener Demonstration Garden. Not only do trainees receive quality training, they also have the opportunity to meet and learn from experienced local Master Gardeners.

For more information, call the WSU Extension office at 735-3551. Applications are due today.

* Marianne C. Ophardt is a horticulturist for the Washington State University Benton County Extension.

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