Winter Desiccation and Browned Evergreens

Winter weather in Minnesota is harsh. Sub-zero temperatures for days on end, sunless days and long nights, and the worst – stinging Arctic winds. Everything scurries for cover from these blasts. Even native Minnesotans hunch and bundle when the stinging winds hit. It feels as though warmth is sucked right out of the body. Not isolated to people and animals, this problem is very real for our beautiful evergreens; we call it winter desiccation.

Winter desiccation is the removal of water from leaves in winter. For deciduous trees and shrubs this is not an issue as they have long since dropped their leaves. Evergreens, however, keep their leaves or needles all winter. During these months, trees are not actively transpiring, moving water from the roots up to the leaves to replenish what was lost. Therefore, if the existing moisture is removed the leaves or needles are left brown and dead or at least dead-looking. Desiccation is at its worst on windy days; water is blown right out of the leaves.

Many species of evergreens, both shrubs and trees, experience discoloration from winter desiccation. Fir and Juniper generally show reddish-brown tips, while Pine and Boxwood turn lighter yellow-brown. Discoloration and damage are generally worse on the sunny, windward side of the plant. If this occurs it does not necessarily mean the plant is doomed. Often, if the plant is given adequate moisture in the spring it will replenish the browned needles, and they will become green again. If the browning is severe there may be dead tips throughout. Rarely will this damage be so severe that the plant won’t recover. I have seen Pine that were completely brown in spring recover fully by mid-summer.

Winter Desiccation on Boxwood | Photo Catherine Nickelson

Boxwoods that are showing damage on the southwest sunny side that is open to winter winds | Photo Catherine Nickelson

Winter desiccation on Arborvitae | Photo Catherine Nickelson

If your evergreen has lost its green over winter don’t cut it down yet. There are a few steps you can take to help it recover. First, ensure it has sufficient water in the spring. Secondly, cut out any branch tips that are completely dead. This can be determined by scraping away some bark on the twig; if there is greenish wood under the bark it is likely still alive and may recover. If there is no green, it is a dead twig; cut it out. Thirdly, be patient. Don’t make a fatal decision until June at the earliest.

There are also steps that can be taken to help minimize, not prevent, damage by desiccation. First, ensure the plant has sufficient water, 1″ per week, through autumn. Second, protect the plant from wind with a burlap cover or screen (this is only practical for shrubs). Third, mulch around the root zone to help the plant retain moisture in the summer. (See our blog post “The Importance of Mulching” for more information).

Though winter desiccation can appear devastating, it has not necessarily destroyed your evergreens. Be patient, and they may come out alright. Take a few extra care measures for next year and they may not be harmed at all.

Catherine Nickelson | Horticulturist | Arborist
Posted 3/11/2020