Minnesota's harsh climate can cause severe damage to landscape plants.

Winter sun, wind and cold temperatures can bleach and dry out evergreen foliage, damage bark, injure or kill branches, flower buds and roots.

Snow and ice can break branches and topple entire trees.

Salt used for deicing streets, sidewalks and parking lots is harmful to landscape plants.

Winter food shortages force rodents and deer to feed on bark, twigs, flower buds and leaves, injuring and sometimes killing trees and shrubs.

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Here are steps you can take to protect trees and shrubs from these different injuries.

Sunscald

Sunscald is caused when the sun heats up the bark during a cold, winter day, then clouds, trees or buildings will block the sun, causing rapid freezing of the bark tissue which results in the cracking of the bark.

Trees with thin bark are often affected by sunscald, including cherry, crabapple, locust, linden, maple, mountain ash and plum.

To protect from sunscald, young trees should be protected with white plastic tree guards or white tree wrap. Do not use brown paper tree wrap or black-colored tree guards, as they will absorb heat from the sun.

Wildlife

Many mammals can damage trees in winter, including mice, voles, rabbits and deer.

If wildlife removes the bark completely around the tree and girdles the trunk or stem, it will kill the tree above that damaged site.

You can install white plastic tree guards, tubes or wire fencing to protect the bark and trunks of trees.

If you have young white pine or white cedar trees, protect them by bud capping. Bud capping involves stapling a piece of paper on the leader or terminal bud.

Fencing around trees, at least eight feet tall, can also be effective.

Young, deciduous trees should be protected from rubbing on the trees from bucks by using tree guards.

Evergreen winter injury

Discoloration of evergreen foliage during winter may be caused by a few things.

Winter sun and wind cause excessive foliage water loss while the roots are in frozen soil and unable to replace lost water, leading to drying out.

Fluctuations of temperature during the warm winter sun and cold nights can injure the foliage. Cold temperatures occurring early in the fall before plants have hardened off completely or in late spring after new growth has occurred can result in injury or death of this non-acclimated tissue. Yew, arborvitae and hemlock are most susceptible, but winter browning can affect all evergreens. New transplants or plants with succulent, late-season growth are particularly sensitive.

How to reduce evergreen winter injury:

  • Prop pine boughs or Christmas tree greens against or over evergreens to protect them from winter wind and sun, and to catch more snow for natural protection.

  • Construct a barrier of burlap or similar material on the south, southwest and windward sides of evergreens. If a plant has exhibited injury on all sides, surround it with a barrier, but leave the top open to allow for some air and light penetration.

  • Do not prune after August as pruning can induce the growth of new foliage.

  • Keep evergreens properly watered throughout the growing season and into the fall. Never stress plants by under- or overwatering. Decrease watering slightly in September to encourage hardening off, then water thoroughly in October until freeze-up. Watering only in late fall does not help reduce injury.

Root injury

Roots do not become dormant in the winter as quickly as stems, branches and buds – and roots are less hardy than stems.

Roots can be protected by keeping soil temperatures warmer and more stable. Moist soil holds more heat than dry soil, so frost penetration will be deeper and soil temperatures colder for sandy or dry soils. Snow cover and mulch act as insulators and keep soil temperatures higher. With newly planted trees, cracks in the planting hole allow cold air to penetrate into the root zone, reducing fall root growth or killing newly formed roots.

Reduce root injury by doing the following:

  • Covering roots of newly planted trees and shrubs with three to four inches of shredded wood mulch.

  • Creating a "donut" of mulch by pulling the mulch away from the trunk about six inches, which will prevent adventitious roots from forming and ultimately girdling the tree.

  • If the fall has been dry, watering heavily before the ground freezes to reduce frost penetration.

  • Checking new plantings for cracks in the soil and filling them with soil.

With a little bit of preparation before winter, your trees and shrubs will come back healthy next spring.

Tarah Young is an interim Hubbard County University of Minnesota Extension educator in agriculture, food and natural resources. If you have any questions about this topic or any others, contact her at 732-3391. If information about agriculture, gardening and natural resources interests you, consider signing up for the Hubbard County UMN Extension Agriculture, Gardening and Natural Resources E-newsletter at z.umn.edu/HCExtensionNewsletter.