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Weather Injury on our Plants

All of Illinois has seen and experienced some very different, and not so typical, weather the last two months, and we are still waiting to see what is next. March and April seemed like weather from late spring and, on a few days, even early summer. Since we had all that warmer weather early, many plants were well along in early spring development when the cold weather and even some frosts hit yet again. Late, or in our case this year early, frost damage occurred throughout the state.

Cold temperatures can outright kill plants like our annual vegetables or flowers if they were in a tender stage or not acclimated. That was easy to spot this year. Many plants were planted because the weather seemed nice, and were not based on our average frost-free date.

On trees and shrubs, cold damage would be limited to the young expanding leaves and stems. They may look distorted, cupped or curled, or have browned margins or spots. Any growth that follows will be normal in appearance.

Visually, leaves may be of normal size yet they look yellow, bleached, or sometimes even white in color. While the leaves were not killed outright, the cells that produce chlorophyll are damaged. As soon as normal, healthy leaves are present, those damaged leaves often will fall off.

Sometimes the damage is mistaken for foliar diseases, but when you examine the leaves, they will not show the signs of the disease. Another clue that the weather caused the problem is cold damage in the home landscape will impact many of the plants there, while a disease is much more host specific. Also, weather-related damage occurs "overnight" while diseases need time to spread.

If there are plants in the landscape that suffered from cold weather damage, giving them some help this year will get them back to better heath. Established plants can be fertilized to replace some of that nutrition lost and should be watered well during the summer's drier weather. There will be a lot of "let's wait and see" going on this year. Buds on woody plants can sprout out well into June as replacements for twigs and leaves heavily damaged by frosts.

If the garden vegetables are in question, any delay in recovery means a delay in flowering and fruiting. Badly damaged vegetable transplants should head to the compost pile in favor of fresh replacements. If the cold soils have delayed germination, or more likely rotted the seeds, be prepared to sow more seed. Be flexible this season out there in the vegetable garden, as it appears to be anything but normal.

Richard Hentschel is a Horticulture Extension Educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. Stay tuned to more garden and yard updates with "This Week in the Garden" on Facebook at