Extreme Cold Weather Has Benefits

February 3, 2019 lawanda Newspaper ColumnsUncategorized

The extended bout of cold weather this past week had many people grumbling and complaining.  Extreme cold does bring good news though.

        Lee Frelich, Director of the Center for Forest Ecology at the University of Minnesota says that extended sub-zero temperatures can kill the larvae of emerald ash borer, the insect that is decimating ash trees throughout the Midwest.  The larvae overwinter in the bark of ash trees, which does give them some protection, between 2° and 7° F. warmer than the surrounding air.  However, the longer the temperature remains low, the less the insulating effect of bark.   A study by the Minnesota Forest Service showed that 5% of emerald ash borer larvae die at 0° F, 34% at -10°F, 79% at -20°F and 98% at -30F.  While this is great news, remember that while the cold may knock back the emerald ash borer population significantly this winter, it won’t completely wipe out the population since some of the larvae will be under bark that is protected by an insulating snow layer and others will be on the south sides of trees which may retain the sun’s warmth. 

        Another insect pest who population that is negatively affected by the cold weather is gypsy moth.  Egg masses are laid on the outside of tree bark or other objects so they are exposed directly to the cold air.  Gypsy moth eggs die at -20 F. 

        Along with the effect on insects, cold weather also affects plants, but in a good way.  Cold winter temperatures are necessary for many of our beloved plants to thrive.  Many native spring woodland ephemerals, prairie plants and favorites from your perennial bed wouldn’t survive or else wouldn’t bloom without experiencing winter.

        In the wild, seeds that are shed in fall spend the winter atop or just under the soil.  They are dormant over winter but their hard seed coats are softened by frost and moisture.  In spring, the seeds’ embryos begin to grow and are able break through the softened seed coats.

        Bulb plants like tulips, hyacinths, crocuses, daffodils, muscari and snowdrops need 12-16 weeks of cold in order to grow and bloom the following spring.  These plants go entirely dormant over summer once they finish their spring show.  Then, when temperatures begin to cool, a natural biochemical process breaks down starches and carbohydrates stored in the bulbs and changes them into glucose.  The glucose acts like an anti-freeze over the winter and then in spring provides the energy for the bulbs to grow and flower.

        Probably the plant most missed by northerners who move south to escape winter is the lilac.  While lilacs can withstand very hot temperatures – as hard as it is to imagine today, it does get over 100° F here occasionally – they can’t withstand a long duration of extremely hot temperatures and they need a long, cold winter to thrive. 

        So bundle up and give thanks for winter.  Come spring you’ll appreciate it even more!


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