Winter in Minnesota can be all over the board: snow, no snow, even rain, and above-freezing temperatures. We have had a very mild fall so far, but homeowners need to have a plan and get ready to prepare their trees and shrubs for winter. Without proper winter care, irreversible damage can be caused which ultimately may result in the loss of your tree or shrub.
Several issues can occur during the winter months including hardiness issues, where the tree or shrub can be killed or injured due to the cold temperatures. Plant selection is critical; knowing your growing zone, even micro-climate areas in your yard is helpful. Microclimates are areas of your yard that may be cooler or warmer due to protection from buildings, low ground or other reasons. Central Minnesota is on the breaking point between USDA growing zone 3 and 4, with Brainerd and Mille Lacs Lake areas being zone 3 and Little Falls and St. Cloud being zone 4.
A common problem is sunscald which is common on young, thin-barked trees such as crabapple, maple, honey locust, linden, and plum. Trunks with unprotected south or southwest exposure often have the winter sun penetrate the thin bark, heating up the cambium layer of the trunk where fluids begin to move, these liquids then will refreeze causing expansion, just like water turning to ice, which cause permanent damage to active tissue.
Winter discoloration on evergreens occurs if evergreens do not have adequate moisture or protection. Winter winds and even the sun can cause desiccation or drying out and browning of the needles. Just like sunscald’s rapid change in temperatures can cause bleaching, injury, or even death on bright, sunny days.
What can be done?
• Continuing to water trees and shrubs until the ground freezes; this is particularly true for evergreens. Watering should slightly decrease in September to encourage hardening off but then water thoroughly through October until the ground freezes up.
• Put on protective wraps or guards. Tree wraps or protective guards can be put around the trunks of young, thin-barked plants; place them on once the ground freezes, and remove in the spring.
• Create burlap screen to protect evergreens. This should be placed on the south and southwest side of the plant.
Residents of Stearns, Benton, Morrison, and Sherburne Counties can direct questions to quincy@umn.edu or call (320) 255-6169, ext. 1.