* TREE AND SHRUB CARE ALERT * 

WINTER DESICCATION INJURY IN EVERGREEN PLANTS

Winter can be a hard time for coastal pines.  Your winter hardy trees and shrubs are for the most part equipped to handle sustained low temperatures, however even the most cold tolerant plants, such as American Holly and Japanese Black pines may show signs of winter desiccation.  Some of the less hardy plants, Arborvitae, Leyland cypress and Euonymus can show severe damage.  Winter desiccation (drying out) occurs when evergreens are subjected to frozen soil and moisture robbing winds.  All foliage loses some moisture over time; if that moisture cannot be replaced through root uptake damage will occur.  Frozen soils prevent plant roots from taking up water.  Damage is usually more extensive on the side of the plant facing the prevailing wind.  This season many plantings had pronounced damage on the northeast sides as well as on the west side.  In some cases the damage is not noticeable until spring arrives and the plants begin to grow.

Factors that can predispose evergreen trees to winter desiccation are 1) light colored rock around the base of the tree; 2) poorly developed root systems due to improper planting; 3) stress due to insects or disease; and tree genetics.

The key to preventing winter desiccation in evergreen trees is to maintain adequate soil moisture beginning in the summer and continuing through the winter.  One of the best ways to accomplish this is by mulching around the base of the tree with organic mulch like coarse wood chips.  Trees should be kept adequately watered during dry periods in the summer and fall.  A tree that has suffered from drought conditions at any time during the year will not be able to withstand winter conditions as well as a tree that has consistently received adequate moisture.  

Think about improving the vigor of plants with an appropriate fertilizer or soil injected humic acid.  Excess nitrogen can increase winter damage next season so timing and rates are critical.  Reducing pest populations will improve your plants chances of getting through next winter undamaged.  Insect pests such as scale and mites can be controlled with horticultural oil.