Winter Desiccation of Woody Ornamentals

B. Rosie Lerner, Extension Consumer Horticulturist, Department of Horticulture & Landscape Architecture, Purdue University

The howling winds and frigid temperatures are challenging for all woody landscape plants, and though our plants are fully dormant at this time, they are still subject to losing too much water from plant tissue, a condition called desiccation. The unusually heavy and consistent snow cover provides good insulation, and most plants went into winter with a good moisture supply this year. But when the ground is frozen solid and accompanied by high winds, the plants continue to lose moisture but are unable to replenish the supply.

Evergreens, and in particular, broadleaved evergreens such as rhododendron, mahonia, and holly are the most susceptible because they have a greater surface area through which to lose water compared to deciduous plants. Broad-leaved evergreens that have suffered from winter desiccation typically have beige to brown leaf edges that are curled or they may show red or purple discoloration. But even deciduous plants (those that lose their leaves in winter) continue to lose water throughout the winter. Severe desiccation will be obvious as dead twigs and buds. Some twigs will leaf out in spring only to die back later in summer as heat or drought stress apply additional pressure.

We recommend delaying pruning chores a bit this spring so that the toll of winter injury can be assessed. Dead tissue can be removed anytime, but cutting into live tissue leaves the remaining stem more vulnerable to further drying.

Figure 1.Arborvitae winter desiccation

Figure 2. Mahonia winter injury

Figure 2. Rose winter dieback