Well so much for the lack of snow cover. Fortunately we had a good amount of snow on the ground before the polar vortex paid us a visit in late January. Snow is an excellent insulator so most of the perennials in our gardens should have been well protected from the -25° temperatures we experienced. That is not to say that some of them with branches above the snow line, such as hardy shrub roses and other woody shrubs, may not have experienced some damage from the record cold. In fact, two cold hardy Minnesota crops, apples and grapes may well be affected by the severe temperatures.
Apple and grape varieties bred by the University of Minnesota were bred to be cold hardy but what exactly does that mean? It means that the plant has the ability to survive the cold temperatures but it does not necessarily mean that it will not suffer damage. Apples such as Haralsons that were developed in the much colder past have proven to be time tested to withstand harsh temperatures. The newer varieties not so much; they have not yet faced a polar vortex of this magnitude. Scientists at the U of MN are predicting that those varieties that show excellent to very good cold hardiness (Haralson, Frostbite, Sweet Sixteen and Honeycrisp) will probably suffer little or no damage in the southern 1/3 and some damage in the northern 2/3 of the state. Varieties that exhibit good or fair cold hardiness (Regent, Snow Sweet and Zestar) will likely experience damage in the south and may even be killed in the north.
Grapes may also experience some affects from the cold temperatures. Older varieties such as Brianna and Swenson Red have had many years of experience with the cold and may be relatively unaffected, but the newer varieties developed by the U of MN have been developed since 1996 and have not yet had a lot of experience with -25° temperatures. Breeders believe that there will most likely be some bud kill and possibly even some woody tissue loss on the vines. However the newest variety from the University, the Itasca, did have a bud survival rate of 63 percent in 2014, the coldest year experienced since it was bred. Even though we may not personally grow apples or grapes we should be aware that this may affect us and the Minnesota economy, by limiting yields and increasing cost for apples in the fall and Minnesota wines (gasp) in the next year or two.
One good thing about this year’s Polar Vortex is that it may have killed many of the Emerald Ash Borers that are infecting our ash trees. Unfortunately it may not have been enough to entirely kill off the invasion, but hopefully it will slow it down. Not so much the other nasty pest, the Japanese Beetle. Since they overwinter in the ground they are all snug and cozy under the snow cover.
Other good news, not related to the Polar Vortex, but great news none the less, the World Wildlife Fund Mexico reports that the population of Monarchs overwintering in Mexico in 2019 is higher than it has been in over a decade! There are 14 colonies of butterflies covering 6.056 hectares of forest area in Mexico for the 2018-2019 season. This is an increase of 144 percent of the 2017-2018 season and the highest number since 2006-2007. This is believed to be due in large part to individual gardeners and farmers planting milkweed and nectar plants to feed the Monarch larvae and adults. But we cannot rest on our laurels as the Monarch population has not fully recovered. We must continue to advocate for increased habitat, a reduction of harmful pesticide use and addressing the issues of climate change if we wish to see the Monarch population return to optimum levels.
And one last reminder for this winter. When applying chemicals to de- ice your sidewalks and driveways go on a low salt diet. Consider the effects of de-icing salt on our plants and waterways and use it sparingly. According to the Minnesota Pollution Control agency it takes only one teaspoon of salt to permanently pollute five gallons of fresh water affecting our fish and other aquatic life. Once it is in the water it is hard to remove it. A U of MN study found that 78 percent of de-icing salt applied in the Twin Cities flows to the groundwater or remains in the local lakes or wetlands. Communities across Minnesota are turning to sand and reducing the amount of salt used to combat iciness. It would be good for us to follow their lead.