Assessing Polar Vortex Damage to Landscape Plants

1/25/2014

How has the extreme cold weather in the U.S. East, starting with the "Polar Vortex" Jan. 2-10, impacted our clients' landscape plants?

In most cases, probably not so much. But we won't know for sure until spring arrives.

Bert Cregg and Jeff Andresen, both of Michigan State University Extension, writes in a recent blog that predicting freezing damage is difficult due to the variety of factors that come into play, such as degree of plant hardiness, severity and duration of cold, conditions preceding the severe cold, etc.

Cregg advises to watch for symptoms including branch die-back, failure to break bud, and even plant death. In some cases, landscapers or homeowners may observe a "snow-line," indicating the depth of snow at the time of the severe cold. Above the line plants may be damaged; below the line they are alive and healthy. The plants that are most likely to be damaged are those that are marginally hardy for a given zone. A common example are Japanese maples, which are hardy to zone 5b.

There are several reasons for optimism, reports the authors, even in areas where temperatures dropped below hardiness zone minimums. First, many plants we commonly use for landscaping are hardy to a zone or colder in most regions.

So in Southeast Michigan, for example, many conifers and other common trees will likely be unaffected

Second, most landscape plants should have been at or near their maximum cold hardiness since the Midwest has had a steady dose of cold weather most of the winter. Plants will gain or lose cold hardiness as weather warms or cools during the winter. When the weather turns cold and stays cold, plants typically achieve their greatest cold hardiness in January and early February. Our most common scenario for widespread cold damage is when severe cold is preceded by an extended warm-up.

Lastly, the extreme cold was preceded by significant snowfall in many parts of the Midwest and Great Lakes, providing an insulating layer of snow that should have protected herbaceous perennials and low lying shrubs.

Assessing and correcting winter damage to trees and shrubs will be a key component of spring activities for many homeowners and landscapers.

Those of us providing services in the Upper Midwest may want to receive regular landscape updates from MSU Extension, by clicking here. It will be providing updates and guidelines and for dealing with winter injury as we move into the spring.

You may also want to access "Wind Chill Doesn't Really Matter to a Plant," another informative blog from MSU Extension.