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Tree Talk column

Help plants, trees bundle up for winter

Tree Talk: The 2019 weather roller coaster may roll on through winter. Here’s how to prepare your plants.

The 2019 growing season has been quite a weather roller coaster. We had one of the wettest Mays on record, followed by extensive flooding coupled with a delayed planting season. By July, the rains had dropped off and it got hot. Looking at the Farmers’ Almanac for the 2019-20 winter, it looks like a wild ride may be in store with a repeat of extremes in temperature and precipitation.

What’s a plant to do? Here are a couple of things we can do to help our woody plants be prepared for whatever winter throws their way.


A plant’s root system is probably the most important component of overall plant health. Healthy roots are the key to healthy plants! Depending on where you were, there was probably some root damage this past season due to flooding followed by dry weather. The roots hairs are very important in uptake of water and nutrients. If these are damaged or destroyed due to flooding, high soil temperatures and/or drought, that plant will suffer.

Once soil moisture levels began return to “normal” in midsummer, plants had the dubious task of repairing and regenerating their root systems. We can help plants do this by providing adequate moisture during dry periods and by providing a good soil environment.

Going into fall, plant roots will continue to grow as long as soil temperatures are warm enough. That means they’ll still need to be watered up until the ground freezes. This summer we had several occasions where we got the typical “1 inch in one hour” rain event and then a week or so of dry weather. Meteorologically, it will go down as a “good rain,” but in terms of soil moisture, a lot of precipitation ran off and never found the soil.

We also don’t want roots sitting in water when a cold snap occurs. Some of us remember the fall of 1991, when we had a mild fall, lots of moisture, and then an arctic cold front came through with January-like temperatures in late October. Roots were damaged as soil water froze. The following spring, a lot of plants leafed out, flowered and promptly died.


You cannot control rainfall or temperature fluctuations, but you can help reduce extremes in the soil. Mulching is easy and effective: It improves water infiltration, protects roots by moderating soil temperatures in both summer and winter, and provides organic matter to improve soil structure and nutrients. Plus, it restricts weed growth and protects the plant from “weed eater blight.”

A mulch depth of 3 to 4 inches is all that is required, and if possible, spread it out to the dripline of the plant. Be sure not to volcano mulch!

Winter damage

Coming out of the 2018-19 winter, I noticed a lot of winter damage to evergreen shrubs and trees. Most had a very definitive line between healthy tissue and brown, desiccated plant parts. This is usually caused by physiological drought and occurs in winter when we have a “spring thaw,” with relatively warm, sunny days (50 to 60 degrees F) accompanied by a light wind or breeze. The soil water is frozen, but the plant is still transpiring and losing water. This condition will be prevalent on the west and northwest portions of plants.

For smaller plants such as evergreen shrubs, place a wind barrier on the side of prevailing winds to help prevent winter drying. A screen of burlap works well. For larger plants such as trees, provide proper watering up until the ground freezes in fall.

With our weather patterns changing and dramatic fluctuations becoming “the new norm,” we need to do more in preparing our plants for harsh conditions. This will ensure they can have a long and healthy life.

Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at

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