After last week’s sobering, subzero weather, I began to think about all of the ways winter in Wisconsin is designed to make the life of plants, particularly woody ornamentals, difficult.
Snow can be a mixed blessing. I like to see a few inches of snow on the ground, because snow actually has an insulating effect. Without a snow layer, soil temperatures can become quite cold far down into the soil profile and this can lead to cold injury to plant roots. Such injury can outright kill plants, or alternatively lead to a slow, painful death where plants leaf out, but leaves rapidly dry up and die because there is a lack of a functional root system to take up water to supply to the emerging leaves.
Excessive snow can also be problematic. In particular, I see situations where white cedars (arborvitaes) become so laden with snow that a variety of problems can arise. In extreme instances, the weight of the snow may be so heavy that branches will snap. In other instances, the snow simply causes the branches to bend downward. This may seem innocuous, but if the snow doesn’t melt away and the plants are weighted for an extended period, branches may not spring back into their normal position and the shrubs end up deformed.
Late January’s deep freeze here in Wisconsin likely led to significant plant damage. Plants have particular ranges of temperatures that they can tolerate (usually described in terms of their USDA Hardiness Zone). If temperatures drop outside of this optimal range, physical injury to branches and trunks, and even plant death can result. As I mentioned above, lack of snow cover can make cold injury worse by allowing for additional cold injury to roots. Another contributing factor can be that many gardeners want to “push the envelope” and grow plants (often exceptionally beautiful trees and shrubs) that are not rated for their hardiness zones, but for warmer environments. Often these marginally hardy plants will do well for many years, until they experience an extreme winter. We’ll have to wait to find out how severe this winter’s damage has been until spring arrives. At that point, we’ll be able to see how many trees and shrubs don’t leaf out or are stone dead. I’m expecting plants like Japanese maple, magnolia, redbud and many types of fruit trees (particularly peach and apricot) to be hardest hit.
Now that temperatures have warmed a bit, I’m seeing some areas of Wisconsin experiencing “wintry mixes” of precipitation. Often this means freezing rain, which can coat branches and, depending on the duration of the rain and the specific temperature, lead to thick layers of ice that can be so heavy that they cause branches to break. Some gardeners, in an effort to prevent this breakage, attempt to knock ice from branches, but this technique runs the risk of damaging overwintering buds. I have fond memories (read EXTREME sarcasm here) of an ice storm in the mid-1970’s that caused substantial tree damage, paralyzed Madison and left my family without power for five days. We spent a lot at the mall.
High winds can cause extensive plant dehydration. I most commonly see this as a problem on evergreen trees and shrubs. I think of windy conditions, alone or in concert with cold temperatures, as being particularly damaging on Alberta spruce, boxwood and white cedar (arborvitae). Watch for brown or bleached needles and branch dieback on these plants, particularly as they come out of dormancy in the spring. This damage in often referred to as winter burn. In extreme situations, high winds can physically damage and break off branches.
Now that I’ve totally depressed you by considering all of the possible adverse effects of winter weather, let’s try to put a sunny spin on things and think of the upside: All of the winter death and destruction provides ample opportunities to plant new and exciting trees and shrubs (and even herbaceous plants), and watch these new plants grow and mature. 🙂