Preparing landscapes for winter
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
With football season in full swing and leaves about to turn color, we come to the sad realization that snow will be flying before too long. Landscape plants in Michigan face an array of environmental challenges, but it’s safe to say that winter is the toughest season for environmental, or abiotic, injuries. This is largely because there are so many different ways that winter conditions can injure plants.
Types of winter injury
Freezing injury: When cold temperatures drop below the hardiness level of plants, freezing injury may occur. In the middle of winter (mid-January to mid-February) plants reach their maximum hardiness and can usually withstand even the most bitter cold. Where we encounter problems is during the winter acclimation and de-acclimation phases. So if we get a record cold night in late November or, more commonly, extremely cold temperatures following a late winter warm-up, we can see freezing injury. Freezing injury usually appears as die-back in the spring. Depending on the plant, die-back may be limited to branch tips or the entire tree or shrub may die-back to the ground-line. When thinking about freezing injury, it is important to remember that roots are much less cold hardy than the above-ground portion of the plant. If you are over-wintering container or B and B material, make sure plants are properly heeled-in to protect the roots for the winter.
Salt damage: Last winter’s heavy snowfall forced road crews to use large amounts of de-icing salt. As a result we had lots of reports of salt damage to plants. Sodium chloride is the most common de-icing material and can damage plants in a variety of ways. Alternative de-icing materials that also contain chloride, such as calcium chloride, also have the potential to cause damage. For small-scale de-icing, consider alternative materials that do not contain chloride such as calcium magnesium acetate. Where exposure to conventional de-icing salt is unavoidable, use burlap or canvas to shield plants from salt spray or splash. Yes, I realize this isn’t always an aesthetically pleasing look, but it the most effective way to keep plants healthy through the winter.
Snow and ice breakage: Heavy snow and ice can wreak havoc on trees with weak branches. Once trees have dropped their leaves it’s an excellent time to inspect the branch architecture of your trees. Look for large limbs with evidence of decay and narrow crotch angles. People that work with hazard tree evaluation think in terms of targets; if a branch failed what would it hit. A questionable branch overhanging your carport or your kid’s bedroom should be inspected by a professional arborist.
Winter desiccation: As the name implies winter desiccation is actually a form of drought stress. It occurs on conifers and evergreen broadleaved plants when temperatures begin to warm, usually in late winter, but the ground is still frozen. As leaves begin to lose water through transpiration, the plant cannot absorb water since the ground is frozen and the plant desiccates. As with salt injury, protecting plants is the best remedy, especially for evergreens on exposed sites.
For more information on these and other environmental plant injuries, please see MSU Extension Bulletin E-2996 “Abiotic Plant Disorders - Symptoms, Signs and Solutions - A Diagnostic Guide to Problem Solving.” The bulletin is available from the MSU Extension Bulletin office or as a full-color pdf file at: http://www.ipm.msu.edu/cat08land/pdf/9-19abiotic.pdf