If phrases like “Polar Jet Stream” send a chill up your spine then imagine what such an event will do to plants and trees in your yard. Add to this the windchill and the general cold – minus 30°F – extreme weather that we have in Wisconsin. But what happens when winter temperatures drop to minus 55°F? Even the native plants around your yard take a toll. This blog focuses on extreme winter weather conditions as they apply to your landscaping.  Here’s a visual map of the hardiness zones for Wisconsin: USDA Hardiness Zones -Wisconsin

Plant Hardiness and Zones

In botany and horticulture, we focus on plant hardiness, which is the temperature window in which a plant will survive. Plant hardiness is about the summer’s high temperatures and the winters average low temperature. An excellent way to visualize this is to think about a tall mountain. At the base are grassland and savannah. As you begin to climb the mountain, the grassland gives way to mixed woodlands or conifer forests. As you climb higher suddenly you reach a spot where the forest stops and mostly what you have are rocks. These changes are because the higher you go on the mountain, the colder it becomes. At some point, it gets so cold that few plants can grow there. The same kind of thing happens to yards, though without the mountain. As winter’s extreme weather gets worse, more plants die from the cold. This is because the winter weather has pushed them past the cold limits of their hardiness zones. This is precisely what we expect to find this spring after the extreme winter weather this past year.

The Turn of Spring

This past winter — 2018/2019 — was rough. In the northern part of Wisconsin, the hardiness zones range from zone 3a — minus 35°F to minus 40°F to zone 4b — minus 20°F to minus 25°F. However, this past winter we saw temperatures driven downward by windchill to the minus 55°F range. What that means is that many landscaped yards are suffering from all of this cold and come spring, homeowners are going to discover that plants and young trees might have died.

The Toll on Landscapes in Winter

Beautiful landscapes add value to properties. Not so, if there are considerable gaps in the treeline or if shrubs are all young. The best ROI for landscape comes from mature vistas with trees that are healthy and tall, shrubs that are big enough to provide a benefit and from flowering plants that light-up a yard and delight us.

At minus 55°F the temperature can put black chokeberry, pagoda dogwood, common juniper, crabapples, and many other woody plants in danger of damage or death. Yet, these plants all thrive to minus 40°F. That is part of the new normal climate here in Wisconsin where zone 3a occurs. To make matters worse, some of these are slow growing plants. Dogwoods, Junipers, and crabapple require some time before they reach their peak of beauty and landscaping benefits. Zone 1a, 1b, and 2a represent climates where the annual average cold hits -50°F or below. The plants that survive in these “wicked” temperatures might be the new norm for Wisconsin landscaping. While that sounds bleak, it really doesn’t have to be. Here’s what to consider when replacing landscaping plants after this freakish winter.

1. Take an assessment of what has lived, what is damaged, and what has died. Sometimes a plant will die in cold not because it cannot stand the cold, but because its location did not support it. Those plants might do just fine with a small structure, windscreen or if planted in a sheltered spot. If all the same type of plant dies during the cold, then those plants are likely not for your yard.
2. Plan for approved plants in colder zones. If you are dreaming of beautiful spring bulbs then consider adding in cold-hardy varieties that can go down to minus 50°F without a problem. Siberian Iris (comes in quite a few amazing colors) is an excellent example as is Lily of the Valley. For bursts of color opt for Cranesbill, larkspur, and yarrow. These plants offer brilliant and beautiful flowers and will take the cold. For smaller trees and shrubs consider the beautiful Dwarf Birch, Netleaf Willow, Quaking Aspen, or the Lapland Rhododendron.

The reality is that there are many wonderful and beautiful plants that can tolerate the freakish and oddly cold winter we just had. To learn more about how to choose the best plants for your Wisconsin yard, reach out to our team at Design Custom Homes. We can put you in touch with some of the area experts.