Friday 29 March 2019

What this roller coaster winter is likely to do to our plants?

Posted by at 11:00 AM in

What this roller coaster winter is likely to do to our plants?

It’s easy to confuse weather with climate.  Weather is the current atmospheric conditions at a given place, whereas climate is the long-term average atmospheric conditions of a given place.  Similarly, many people confuse climate change with global warming. Average annual temperatures in much of Wisconsin are already 2 degrees F warmer than 50 years ago, and climate models predict that average temperatures are likely to continue increasing, both globally and in Wisconsin.  This can entice gardeners to try plants adapted to warmer climates. This is risky, though, because a warmer climate doesn’t mean that temperatures will always be higher than in the past. Wild oscillations in weather – like record high and low temperatures, droughts, torrential rains, and so on – can mask longer term changes in climate.

This winter has been a perfect example of why some people prefer the term “climate weirding” to “climate change.”  In Wausau, October had twice the normal rainfall and was 3? F colder than average, including a plunge from 77 degrees F on the 9th to a hard freeze on the 12th.  November and December had near normal precipitation, but November was 6? F colder than average and December was 4.4 degrees F warmer than average.  As a result, we had more rain than snow in December, with never more than 3 inches of snow on the ground. The near absence of snow cover continued through most of January, despite it being 2.3 degrees  F colder than average.  Fortunately for our plants, several inches of snow had fallen before the late January polar vortex, when lows in Wausau dropped to -27 degrees F for two nights in a row. Three days later, temperatures soared to 40 degrees F and it rained hard, then froze again.   As of mid-month, February has been about 2 degrees F colder than average but we’ve already received three times the normal precipitation for the entire month.

So, how are our plants likely to ride out this winter?  Our polar vortex temperatures were only 2 degrees F colder than expected for USDA Plant Hardiness Zone 4b, like Wausau, and they came when plants should have been fully hardened off.  However, the abrupt drop in temperatures in fall and the cold temperatures in December and January with limited snow cover may also have been hard on our plants. A cold-damaged plant may simply not leaf out when spring comes.  Other times, parts of the plant or the entire plant will leaf out normally, then quickly wilt and die. My plan is to simply wait and see. Any die-back that’s evident by late-spring or early-summer can be pruned out then. Let’s hope our plants are tougher than we are, and that they’ll delight us with greenery and blossoms and fruit, just as they always have.

Written by Professor Paul Whitaker, UWSP-Wausau