Winter Dessication of Evergreens

The Plant and Insect Diagnostic Clinic has recently received specimens of pine, spruce, fir, yew and other evergreens. Symptoms on plant specimens vary from yellowing or browning of needle tips to complete yellowing or browning of needles. On concolor fir, one-third to one-half of each needle has turned brown (Fig. 1). Clients describe the problem as appearing on one branch, a few branches, or one side of the evergreen (usually the side facing prevailing winds). The damage is attributed to winter desiccation (also called winter burn, winter drying, or winter scorch). During the winter months, the roots of evergreens are not able to absorb water from the frozen soil. However, evergreen needles continue to lose moisture throughout the winter. Considerable water loss can occur on windy or sunny winter days. Damage occurs when the needles lose excessive amounts of moisture. Poorly developed root systems, girdling roots, root injury, soil compaction, and heavy clay soils are some factors than can predispose evergreen trees to winter injury.

 

Will the tree survive?

 

Evergreens exhibiting winter injury may still have live buds. Live buds will break in spring and produce new growth. By late June or July, evergreens that have suffered minor damage should look much better. Prune out any branches or branch tips that are completely brown after the new growth begins to emerge in spring. Those branches that are completely brown are most likely dead. Make the pruning cut just above a live branch or bud. Remember to remove dead branches as they can harbor insects or fungi.

 

What to do to prevent winter desiccation?

 

To prevent winter desiccation, it is important to maintain adequate soil moisture by watering evergreens once a week (during dry periods) to allow them to growth vigorously throughout summer and into fall. Deep watering in fall is especially important if rainfall in late summer and fall is well below normal. Another practice that may reduce the risk of winter injury is to apply a 3 to 4 inch layer of wood chips or shredded bark around the base of evergeens. This will help conserve soil moisture and prevent deep freezing of the soil in winter. Trees exposed to prevailing winter winds can be transplanted to a more protected location.

 

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