There has been a lot of media coverage and homeowner concerns about boxwoods, and this has overshadowed overwintering damage on a range of other landscape plants from trees down to small fruits and perennials.
First thing's first – winter hardiness. To some extent, gardeners have been cheating Mother Nature annually for years. We have this USDA hardiness zone map to use as a guide and the information on the plant tag to tell us if the plant is going to survive our winters. The hardiness zone map has been revised a couple times now so you want to use the most current one as a reference. The changes reflect long-term weather patterns over many years. Visit the USDA site at https://planthardiness.ars.usda.gov/ and zoom in on Illinois or search by zip code. For example, St. Charles with a zip code of 60174 registers as zone 5b with a temperature range of -15 to -10 degrees Fahrenheit for winter lows.
Where we get into trouble is purchasing a plant that is out of our range. The kind of plant can make a difference too. Boxwoods are a broadleaved evergreen, more susceptible to winter damage than a deciduous shrub in the same zone. The same goes for rhododendrons and versions of the broadleaved azalea.
This spring we are seeing winter damage on a variety of plants. Bud and twig dieback is common for trees and shrubs, especially at the tips where those buds were created late in the summer. Yellowing and needle loss on yews and larger-needled evergreens can be seen. We also may notice a loss of bloom show on forsythia, ornamental pears and flowering dogwoods. In addition, if you have perennials that typically overwinter with some above ground stems, they may be killed down to the ground.
In the home orchard, apples are the hardiest (flowering crabapples are an apple so they are fine), and peaches are the most sensitive. While there have been peaches survive this spring, there are many more that have suffered severe damage to death. Other small fruits like brambles, strawberries, and blueberries have suffered to varying degrees.
In the order of damage, sensitive plants will lose flower buds first, then vegetative buds if the severe cold weather continues, then twigs and branches. For plants that have a good reserve of nutrients, it can replace vegetative buds, as long as there is no other damage. It will be late May into June before we know for sure.
Dead wood will not come back, so pruning it out is appropriate. If you take the wait-and-see perspective, get the replacements in as early as you can to allow the new transplants as much time as possible to establish new roots in your yard.
This damage is widespread throughout the region and there was not much that could be done to prevent this kind of cold weather damage. For those gardeners who did protect their sensitive plants from winter sun and wind, nothing could be done to protect them from the very severe low temperatures. For those who believe in alternative dimensions, you were not alone this winter.
About the author: Richard Hentschel’s expertise extends across several subject areas with specialties in lawn care, fruit tree production, woody ornamentals, and home and community gardening. During his 45-year career in horticulture and agriculture, Hentschel became a well-known and respected expert for commercial and homeowner audiences, industry organizations, and media. He retired from University of Illinois Extension in April 2022 with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois.