We should have been expecting it, but no one is really ever ready for the first really cold weather we get. Our hardy trees, shrubs and evergreens or perennials weren't really impacted by low 30's and upper 30's that areas in the Fox Valley received. Gardeners do plant lots of tender flowers for their color, texture and habit that make our gardens shine, yet can be much more sensitive to cold temperatures.
Impatiens have been struggling a bit in the landscape with the cooler temperatures we have had this summer anyway, so the cold temperatures could have finished them off for the season in the more exposed garden locations. Impatiens would not have collapsed unless the temperatures did drop to freezing, but foliage loss can easily happen. The upper and more tender foliage of Cannas are the most affected when exposed to cold temperatures. One great example of cold damage is the wilting of foliage on sweet potato vine. While it did not hit freezing this time, plants that are more tropical like the ornamental sweet potato vine and the garden varieties are quickly impacted. This time they remained wilted for a couple of days before coming back. There can also be some discoloration as well.
If garden varieties of sweet potato are grown, the tubers need to be harvested immediately after the foliage is hit by a killing frost and then cured as normally done. Other summer bulbs you would think would be hurt seemed to be fine. Calla lilies and Amaryllis showed very little damage if any. In natural areas, our native plants took this cold snap without a problem and will continue to prepare for winter dormancy.
As we continue to have colder night time temperatures coupled with warm daytime temperatures, color will show up in a lot more places. Some the intense color already in the landscape is due to the genetics of our landscape cultivars. Propagated from plants demonstrating strong and consistent fall color regardless of moisture and temperatures, these plants give us outstanding fall color every fall season. In nature with the diverse genetics, fall colors can be quite different year to year.
Now that we have had our first experience with cold weather this fall, it would be good to start the garden clean up to stay ahead of the weather. October weather can change quickly. Besides the clean-up, attention to newly planted ornamentals should continue to ensure establishment continues well into late fall. Trees, shrubs and evergreens for example will continue to develop new roots until the ground actually freezes; spring flowering bulbs do the same. Before filling those landscape waste bags, use the garden debris to fill the compost bin or build the compost pile. Enjoy the crisp fall weather, great fall colors as your landscape changes from summer to fall to winter while working your yard over the next few weeks.
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.