Released November 10, 2009
COLUMBIA, Mo. –Missouri horticulturists remember Veterans Day, Nov. 11, as the date of two massive freeze events that damaged trees and shrubs across the Midwest.
“Many of us begin to worry at this time of year, wondering if we have done all that we can to encourage our landscape plants to develop dormancy with its associated cold tolerance,” said Chris Starbuck, University of Missouri Extension horticulturist.
On Nov. 11, 1911, an arctic cold front moved through Missouri so quickly that the temperature dropped from a then-record high of 82 degrees to a record low of 13 that same day. Some areas in Missouri recorded a 30-degree drop in 30 minutes. There was rain, sleet and snow. Hunters reportedly froze to death before they could reach shelter.
The Armistice Day blizzard of 1940 hit on Nov. 11 after a warm, wet fall, dropping the temperature from 60 degrees to about 10 degrees within three hours. Temperatures dropped below zero by the morning of Nov. 13 in some parts of the state.
This combination of a warm, wet fall and a sharp drop in temperatures inflicted massive damage to woody plants all over the Midwest, destroying most of Missouri’s fruit trees in a single night, Starbuck said.
Prevention
“We should avoid certain horticultural practices that make our landscape plants more vulnerable to an early, rapid freeze event,” he said.
During fall pruning, don’t remove more than 5 percent of the plant’s branches. This can have an invigorating effect that could delay dormancy.
Even if no bud growth appears, pruning may stimulate activity in the cambium, which is the layer of cells between the wood and the bark. This can lead to freeze injury near the pruning cut. Perform major pruning only during the dormant season.
If you plan to add mulch to trees and shrubs, Starbuck suggests waiting until early December. This will allow the soil around the plants to cool, promoting dormancy.
When adding mulch, Starbuck said, make “bagels,” not “volcanoes.”
“Mulch can be several inches thick a foot or two away from the trunk, but never more than an inch next to the trunk,” he said.
Evergreens may be vulnerable to desiccation injury during winter. When soil stays wet for long periods, some deep roots may suffocate, resulting in a shallower-than-normal root system.
Consider watering the evergreens after long periods of low temperatures with no precipitation. Cold winter winds continually remove water from the leaves of evergreens. Make sure to mulch your evergreens well after the surface of the soil starts to freeze.
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http://extension.missouri.edu/news/DisplayStory.aspx?N=571
Source: Christopher J. Starbuck, 573-882-9630
Editor: Robert Thomas, 573-882-2480, thomasr@missouri.edu
