Issue 17, October 22, 2013

Water Now to Help Prevent Winter Burn to Evergreen Trees and Shrubs

In the May 13th issue of the newsletter I wrote about winter burn, a form of winter injury that commonly affects broadleaved evergreens such as rhododendrons and boxwoods. This type of injury can also affect narrow leaved evergreens such as yew, arborvitae and hemlock. It is more severe on drought stressed plants. Last year's drought and dry start to the winter likely contributed to the symptoms of winter burn and even the death of many evergreens in our area.

As a reminder, winter burn occurs as the amount of water lost from the leaf tissues exceeds the amount the roots and stems are able to transport. During the winter months, photosynthetic processes of evergreens are slowed, but the plants continue to lose water.  Dry or frozen soils limit the water available to trees and shrubs to uptake. Dry soils can be even more damaging as the soils tend to freeze more deeply. Plants located in areas unprotected from desiccating winds are also commonly affected.

Though we cannot control the weather, or how cold it will get, we can take a few steps to prevent this type of injury.

  • Maintain adequate soil moisture. As most of the state is currently under some degree of drought, trees and shrubs, especially evergreens, need adequate soil moisture before going into the winter season. Check the soil moisture around plants. Irrigate as needed to a depth of 18" for most shrubs. During dry winters, supplemental irrigation during winter months may be required. Irrigate during warm spells when the ground is not frozen. Water early in the day and do not allow water to collect and stand near the trunk where it may freeze and damage the plant. Mulching will also help to insulate the soil and conserve soil moisture.
  • Select an appropriate planting location. Rhododendrons other susceptible evergreens should be located where they receive partial shade and protection from desiccating winter winds.
  • Build protective screens to provide shade and windbreaks. They can be constructed with burlap or other materials. Temporary fences, such as snow fencing, can also be effective.

Rhododendrons also have mechanisms to help protect their leaves from winter injury. You may have observed rhododendron leaves rolling, curling, and drooping on cold winter days. This action is normal and reduces the amount of tissues exposed to direct sunlight and desiccating winds. (Travis Cleveland)

Travis Cleveland

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