Polar Chill

As many gardeners, farmers and vinters well know, the United States Department of Agriculture has given us this nifty little tool called a zone hardiness map. It divides the US into eleven hardiness zones; each zone ten degrees warmer or colder than the next. The designations are based on the average annual minimum temperature or the coldest temps that can be expected in that area.

I've long been interested in grape cultivar selection and breeding as they relate to the Missouri climate. In 2006 the area where I live increased from Zone 5 to Zone 6 on the USDA hardiness map. This map at the National Arbor Day site demonstrates the changes that took place nationwide. The most familiar wines on store shelves such as chardonnay, merlot and cabernet, come from grapes that belong to a family called vitis vinifera. They're grown in milder climates such as California, Italy or France. Up until recently, these vines were almost unheard of in Missouri but there have been many vineyards in the Midwest pushing the envelope with good success.

As in many other parts of the country, 2010 has brought record breaking cold to Missouri. With temperatures hovering near zero, last week we went to -4F in Boone County. Last night set a record -12F. The last time it came close to this low was in 1962 at a full six degrees warmer. St. Louis experienced its first below zero temperatures in a decade. Other areas of Missouri have recorded even lower temps. While there are many factors that influence how well a vine might fare through a difficult winter, there are no doubt many grape growers anxious about this extreme weather. Research indicates hybrid grapes can experience bud injury below -5F and once temperatures drop to below -10F, things can become critical. On the other hand, vitis vinfera is a different story. Some report Cabernet Franc and Riesling as two of the most hardy, yet they are only considered so down to about -5F. Once you reach around around -12F to -16F there may be significant injury.

I am concerned about my fledgling vines. I planted rooted cuttings in nursery beds last spring but I also planted some in pots. Those pots are mulched in frames which will afford them some protection. I can only hope that protection is enough. There's really no use in being consumed by anxiety. We can't control the weather nor can we change the cold.