Do your evergreens have winter burn?
Winter burn can be a serious problem for evergreens. After the cold and windy winter we had, signs of winter burn abound on evergreen shrubs and trees. There are some broadleaved evergreens such as azaleas and rhododendrons in our zone 3 area, but most of our evergreens have needles.
The most obvious symptom of winter burn is browning of foliage on the south, southwest, and windward sides of plants. Sometimes, however, the plant appears bleached by the sun. Also obvious is how deep the snow was around evergreens. If the bottom branches were buried under snow, they are protected from winter injury while the plant parts above the snowline are damaged by the wind and sun.
Winter burn happens because of transpiration, or water loss, from the plants during winter. Both deciduous and evergreens prepare for winter through the process of hardening off. The plant stops growing and slows down its rate of transpiration and consumption of nutrients. Deciduous trees and shrubs drop their leaves and transpiration stops.
Evergreens retain their foliage and transpiration continues. On warmer sunny days the cells of the foliage thaw even though the temperature is below freezing. The temperature falls at night and damages the cells when they refreeze. Leaves gradually dry, die and turn brown. In extreme cases the entire plant may die. Wind can also cause damage. Continuous drying, cold winter winds can evaporate any moisture the tree has preserved during the hardening off process. Over time the foliage will become desiccated becoming brown and dead.
What to do now? Be patient. The University of Minnesota Extension Service recommends examining the buds. Are they still alive? Where the buds and stem tissue are still alive, the new foliage will regrow to replace winter burned foliage. Wait for the first flush of growth before deciding what needs to be pruned. The buds on the spruce in my yard are showing new growth right now. On the other hand, if buds and stem tips were severely damaged, branches should be pruned back to one-fourth-inch above a bud in the live portion of the plant. If there are no signs of new growth, it is likely the evergreen will have to be removed.
To prevent winter burn in future years, keep evergreens sufficiently watered through the fall until the ground freezes. In Minnesota, this can be as late as November. Place mulch around evergreens to help retain soil moisture. Reduce exposure to sun and wind damage by protecting those plants in exposed sites using burlap, snow fencing or other materials. Avoid planting evergreens on the south or southwest sides of buildings or in any site with high exposure to winter sun and wind.
If you still have winter damage brown spots in your lawn, it is not too late to repair them. Clean up the dead grass, loosen the soil with a garden rake or garden claw then plant a mix of Kentucky bluegrass and fine-leaved fescues such as creeping red or hard fescue. If you like clover, you might mix in a little with the grass seeds. Remember to keep the plantings watered well. Don't mow them until they are well established.
Reference the University Of Minnesota Extension Service website, www.extension.umn.edu/garden/yard-garden/, for more information on horticultural topics. In addition, local Master Gardeners will again answer your questions on home horticulture. Call (218) 444-7916, leave your name, number and question and you will receive a return call.