Monday, March 12, 2018

Winter Desiccation of Evergreens

Winter desiccation, photo courtesy Purdue University
It’s been a typical Jefferson County winter with periods of warm, windy, low-humidity days with no snow cover and extended dry periods. This contributes to “winter desiccation” on needled and broadleaved evergreens. Last year’s transplants are especially prone to winter desiccation (also called winter burn) under these conditions.  As the plants hold their leaves, they continue to transpire which becomes difficult during warm, dry winter periods. Below ground, small “hair roots” may die in dry soils leaving roots unable to replace lost leaf moisture.

The resulting water deficit causes leaf scorch of broadleaf evergreens like Manhattan euonymus, pyracantha, Oregon grape, holly and English ivy. Needled evergreens, especially Dwarf Alberta spruce, certain junipers, and arborvitae, may develop extensive needle browning. Pines show needles with a “half green, half brown” look. 

Desiccation symptoms may be worse on evergreens in difficult sites such as windswept areas, roadsides or medians, southwest sides of buildings, and those with limited rooting areas. Symptoms often appear on the most recent growth that is more succulent and prone to drying.

Next year, be sure to water in the fall to send evergreens into winter with good soil moisture. Now, and every winter, water again as dry periods extend (generally over a month).

For more information, see CSU Extension’s Fall and Winter Watering.