If you hadn't noticed, it's been cold. Maybe not colder than an average NW Minnesota winter, but cold enough. Trees, along with all other plants, have listings that they fall into as to what cold or heat they can survive. This listing is put out by the USDA and organized by cold hardiness.
Here in Crookston we are in Zone 3b. The zones range from 1-coldest to 11-warmest. There are other factors that influence the chart, but to be simple, temperature is the main measuring factor. The temperature that trees can withstand does not depend on the parts that are exposed. Cold hardiness is what the roots can withstand. That is why trees can survive very cold temperatures in areas that get more snow than areas that get the same cold but have less snow cover. This will also explain why potted plants above ground will not survive the winter, when the same plant in the ground will.
On a year like this with little snow and extended cold, some younger trees or other trees that are borderline for our zone may have some dieback or may not survive. Now don't be alarmed about that new crabapple, there are tricks that can be done to help trees make it through a tough winter. Just like the septic tank or shallow pipes, laying down straw will help insulate the soil. However, it could kill the grass, and you will probably have to remove the straw in the spring. The best overall solution is to add a mulch ring around trees. This will help keep the soil warmer, while adding valuable nutrients to the soil and keeping the soil moisture up in the summer. Also the mulch does not need to be picked up each spring when put in a ring around the tree.
Recently, the USDA has come out with an updated Zone map. This map has actually decreased the colder zones now making some areas a higher zone than previously listed. Without getting into the global warming debate, this may open up an avenue to plant some varieties of trees that normally were not planted here before. It may be an adventure and a bit of an investment to try but it is always nice to have something new in the landscape.
By Sam Kezar, Certified Arborist
Sam Kezar, M.S. in Arboriculture, Member of the International Society of Arboriculture (ISA) and Minnesota Society of Arboriculture and ISA Certified Arborist, MW 4503AT.
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