Q: When did it get this cold last? It seems like the last few winters have been milder. Will some plants get hurt?
A: The easiest and best way to answer this is to use a single weather station for the data. The best one I could find for Jefferson City and Columbia is on the south side of Columbia at University of Missouri’s South Farm. (All of the University of Missouri’s weather stations’ information can be found at agebb.missouri.edu/weather/stations/).
The morning was, ironically, New Year’s Day, at -9.8 degrees Fahrenheit. This was followed by -7.6 degrees the following day and preceded by two days -2 degrees the week prior. The last time it was this cold was the winter of 2013-14. It was a dandy, with two mornings -10 degrees (Jan. 6 and Feb. 7), and between Jan. 2 and Feb. 11, there were 10 mornings below zero. This included a lot of snow cover, too. Brrrrr!
Last winter had some potentially damaging temperatures, but they were fairly brief and didn’t set any record, so most folks didn’t realize it. This same weather station recorded three temps below zero: Dec. 18-19, 2016, at -3.2 degrees and -4.5 degrees, and two more on Jan. 6-7, 2017, just below zero. The winter of 2015-16 had one morning just below zero and the winter of 2014-15 had two mornings below zero, in January just below zero and another Feb. 19 at -3.1 degrees.
Some plants may be impacted. Those most at risk are woody plants hardy to zone 6, but not zone 5. The lack of snow cover increases this potential, as it insulates and moderates the depth soil freezes. As of Jan. 7, soil was below freezing to 6 inches deep (the deepest the weather stations record). On the positive side is we had cold weather before it got really cold, so most plants should have adapted to the cold.
Some varieties of peaches may suffer flower. The likelihood of winter burn or damage to evergreens is increased, especially with the dry fall conditions. This would be pronounced on exposed plants or ones newly established.
Q: I heard the fall was dry? How dry was it?
A: It was a very dry fall, with less than 5 inches of rain Sept. 21-Dec. 21. Normal rainfall would be about 10 inches. The rather warm temperatures at the end of September pulled down soil moisture levels and they didn’t recover much in October. Since Nov. 1, there’s been less than 1 inch of rain. Soil moisture starting the new year was quite dry.
Q: How important is it to sterilize your gardening tools, and how often should it be done?
A: When garden tools are used infrequently, there is less risk, as bacteria, viruses and fungi typically don’t survive more than a few hours or days on a surface. Many diseases are not transmitted between unlike plants, such as from a tomato to an apple to an evergreen. The risk increases when a lot of pruning is done on the same plants (e.g. apples) and one of those plants has a disease easily transferred (e.g. fire blight, a bacterial disease). In those instances, it becomes important to disinfect the tool between the diseased plant material and healthy.
One easy step is to always prune any diseased plant last and then not use the tool for several days. To sterilize a tool, use a 10 percent household bleach solution with water or use rubbing alcohol. An easy way is to have two pruning tools and pull one out (to use) and put the one just used in. This tactic is generally only used in high-risk situations like pruning an apple tree with fire blight, where the tool should be disinfected between each cut.
Sometimes one can spread a disease in a way that a tool might be blamed, but it might be something else. An example is rose rosette disease, which is transmitted by a tiny mite. The mite can easily be brushed off onto ones clothes and moved to an adjoining plant. There has been concern the sap on a pruning shears may transmit this virus like disease, but it has never been proven to occur.
Q: Can a 3- to 4-inch diameter tree about 12 feet tall still be straightened up?
A: It should be possible. Pull it straight after winter has abated, toward the end of February. Remove the supports in the fall. You might pull it just a tad past straight, as when you release the support, it will likely move back a little. Contact our office if you need ideas on what to use to support or pull it back with.
Next week’s column will take on the vexing question, “Will the cold weather kill off any summer insect pests?”