Wisconsin Winter – Love It or Leave It
Written by: Jean Ferdinandsen, Certified Arborist WI-0149A
Some of us may leave Wisconsin for the winter months to warmer climates. But our trees, shrubs, and landscape cannot leave. They must deal with whatever mother nature deals out, and whenever she chooses to do so.
Trees and shrubs acclimate best to cold temperatures in the fall with a slow, steady drop in temperatures. Once acclimated, trees can readily withstand cold, nonfluctuating temperatures. The range of low temperature extremes they can withstand is referred to as “cold hardiness, as rated by the USDA (United States Department of Agriculture).
Even if a tree or shrub is rated for our cold hardiness zone (generally zone 5 in our area) it may still be subject to winter and cold damage. Rapid or excessive drops or fluctuations in temperature are the most damaging. Other factors that may influence whether your tree or shrub is winter damaged may be; the frequency and duration of the cold; species or cultivar; location and growing conditions; degree of establishment; and the timing of the extremes.
Examples of cold damage and other winter injury can include:
Frost cracks: These appear as vertical cracks on the trunk or stems, also called radial shakes. These occur most often on the south or southwest side of young or thin barked trees. On sunny days they warm up and then the bark and wood do not cool at the same rate when the sun sets. These cracks occur at temperatures below 15 degrees. The cracks can expand and contract with fluctuating temperatures and may never fully close
Sunscald: Damage occurs under similar conditions that produce frost cracks, but damages a larger area. Cells die and leave an area that appears sunken and the bark may begin to peel away.
Winter burn: Evergreens lose moisture even in winter due to transpiration. Frozen soils and sap do not allow trees and shrubs to replace this moisture loss. Desiccation shows up as browning or scorching, especially on the tips, margins, or more exposed areas (usually south or south west facing).
Root damage: Roots are not as cold hardy as above ground portions. Extreme temperatures or exposure (e.g. in an above ground planter) can lead to roots being killed. This root loss can lead to decline.
Salt damage: Salts used for deicing may leach into the soil or be sprayed onto buds. Both can cause tissue damage and death.
Girdling by animals: Deer and rodents need to eat too. When food is not available due to snow cover, they may chew on the trunks (mice & rabbits) or browse on the tops (deer and rabbits)
Frost heaving: Root balls may raise or heave with expansion and contraction of soil. This occurs primarily with very small root balls and perennials.
Spring freezes: Freezing occurring after growth has begun can damage tender buds, shoots, and leaves. If this occurs when trees are budding out, just parts of the leaves may be frozen leaving holes or ragged margins known a “taters”. Leaves and shoots with cold damage appear water soaked, flag, and wither. Flower buds may be damaged, reducing fruit production,
Snow and ice: Both add weight to branches causing them to break or splay out. Avoid attempts at knocking off accumulations of snow or ice, as this may actually cause more damage.
In many cases, trees and shrubs will recover from cold damage if not too severe. You can’t control nature but you can take steps to minimize cold damage.
- Make proper plant selection and for each site.
- Avoid Installing evergreens and perennials too late in the season.
- Water appropriately, and continue until the ground freezes.
- MULCH, to moderate temperatures and moisture.
- Reduce exposure for sensitive species by avoiding south or southwest exposure or windy areas.
- Prune regularly to develop good form and structure.
- Reinforce weak structure and codominant stems and trunks
- Control grass and weeds at the base of trees and shrubs to reduce habitat for rodents
- Protect trunks with tree wraps and/or fencing. Note: these should be put in place in fall and removed in spring. Do NOT leave wraps on trunks during the growing season.
- Use evergreen boughs or burlap to protect plants
- Apply anti-desiccants in late fall and repeat during winter if needed.
- Reduce the use of deicing salts. Apply them only where needed, choose more plant friendly products. Select salt-tolerant plants where exposure is higher, such as near sidewalks and driveways.
My son’s daycare used to tell the kids “you get what you get and don’t have a fit”. If you take that approach to the weather which we can’t control, perhaps that might help. Your Wachtel Certified Arborist can also help you with plant selection, maintenance, care, and strategies to help reduce winter damage. Give us a call with your questions and concerns. Spring is coming.