Open Winter Injury

John Wilson

By John Wilson, Extension Educator

We are in a very similar situation to where we were about this time last winter. While most of us are enjoying the lack of snow and wondering how long it will last, many plants in our landscape are suffering because of the “nice” winter. A winter with little precipitation and no snow cover increases the risk of winter dessication injury to plants.

Many of you may remember this from last year when perennials and woody ornamentals failed to green up in the spring. Evergreen trees and shrubs are most susceptible, but lawns and perennials can also be injured. Tender and marginally hardy plants were hardest hit.

When there is little snow cover, questions about the need to water during winter rise. While winter watering can be done IF the ground is not frozen and air temperatures are above 40 degrees Fahrenheit, it is important to understand winter watering, even rainfall or melting snow, can also cause plant injury.

For example on lawns and herbaceous perennials, plant crowns absorb moisture and rehydrate. If a rapid drop to freezing temperatures occurs soon after, water taken up by the plant crown freezes. Ice crystals that form then damage or rupture plant cells, and possibly cause death.  This is known as crown hydration injury. It sometimes occurs naturally in late winter when snow is melting, or when an early spring rain is followed quickly by freezing temperatures.

If you would decide to irrigate when soils are not frozen and air temperatures are above 40 degrees, be sure to apply water about mid-day so it has time to percolate into soil before freezing occurs night. Avoid excess watering so it does not pool around plant stems.

If you decide to do winter watering, evergreen trees and shrubs should be a priority. Evergreens are most susceptible to winter drying and more costly to replace if severely injured or killed.

While all plants continue to lose moisture during winter, evergreens lose more moisture due to their foliage being green all year. It is not uncommon for evergreens to turn light brown after spring arrives.

The most common cause of spring browning is winter drying, not cold temperatures. The evergreens Arborvitae and Japanese Yew are most likely to sustain winter dessication injury. Any evergreen grown in a high wind area, near pavement, or on the south side of a home is also more susceptible.

Correct summer and fall watering is most important in preventing winter dessication on evergreens. Water could be applied during winter if dry conditions persist. Again, only water when the soil is not frozen, air temperatures are above 40 degrees F, and at mid-day so water soaks into soil and does not pool and freeze around plant crowns at night.

For valuable plants growing in exposed location, a physical barrier made of burlap, weed barrier fabric, or snow fencing can still be put into place to provide protection. Anti-transpirant sprays could also be applied according to the label. Mid to late winter is often when the majority injury due to dessication occurs.

If evergreens turn brown, owners wonder about plant survival. If only the foliage dies, the plant should leaf out again in spring if buds are viable. If woody tissue is killed, that portion of the plant will not recover. When injury occurs, wait until late May before pruning or removing winter injured evergreens to allow time for regrowth.