Cold Weather, Dry Weather Stressing Grapes
John Marshall, one of the original wine grape growers in Minnesota, says the last time his grapes suffered winter injury was 1996. The winter of 1996 was among the 20 coldest recorded winters in most of the Midwest, but not nearly as cold as the winters of the mid and late 70’s.
Marshall thinks it will take temperatures lower than -25F to damage his wine grapes. The Sunday forecast low for LaCrosse, Wisconsin, which is near Marshall’s vineyard, is -24F.
Marshall says he is more concerned about his Somerset Seedless table grapes than his wine grapes. He grows mainly cold hardy grapes like Frontenac and Prairie Star that can tolerate extreme cold.
See related story: Winter Vineyard Tips
Farther east in Ohio, Patrick Pierquet, who is with the Ohio State University in Wooster, says this cold snap could be useful for “weeding out the weaklings” in the University’s experimental vineyard.
Pierquet adds that the cold weather across the Midwest during December might have been more damaging than the current chill because grapevines were not fully acclimated at that time.
Despite the current cold snap, recent evidence suggests the Midwest is getting warmer. During January of 2012, the USDA released a new plant hardiness zone map and most of the zones shifted north. While the USDA says the zone map is not a good way to determine climate change, many people interpreted the growing zone changes as evidence of a warming world.
The forecast low temperatures during the next few days are not expected to exceed the USDA’s new extreme minimum temperature guidelines, although it will be a close call across the upper Midwest. The USDA’s plant zone map is based on 30 years of data, so it’s not an airtight guarantee that it won’t get colder than “normal.”
Then there’s the proposition that alleged climate change is changing global wind patterns. Whether that’s true or not, when it’s warm and dry along the Pacific Coast, it’s often cold and miserable in the Midwest. (The forecast for San Francisco today is 66 and sunny.)
According to legendary WGN-TV weatherman Tom Skilling, weather systems are usually about 2,000 miles wide. So if warm air is going up the West Coast, then cold air is often coming down the other side of the same weather system into the Midwest.
Jet stream wind patterns have not been favoring rainfall in California recently and the situation is on the verge of becoming serious. Over the past nine months, rainfall in the Sonoma area totaled just over two inches.
On Tuesday, the Sonoma County Water Agency cut the flow of the Russian River by 30% to preserve water supplies. Water from the Russian River is used extensively for summertime vineyard irrigation and springtime frost protection in a vast grape growing area that includes part of the half million acre Sonoma Coast AVA.
On average, annual rainfall in Sonoma is about the same as the rainfall in Traverse City, Michigan. Precipitation patterns in the two areas are very different, however.
Rainfall in Traverse City is more evenly dispersed over the year than rainfall in Sonoma. More than half of the rainfall in the Sonoma grape growing region occurs in December, January and February. If it does not rain during the next two months, rainfall during the Sonoma growing season will almost certainly not make up the difference. (Imagine a place where it does not rain for months!)
Of course, Traverse City is not immune from bad weather. Forecasted below zero temperatures will be the first exposure to extreme cold for many vinifera vines that have been planted in the past five or so years. When grapes like Pinot Noir and Sauvignon Blanc were planted in Northern Michigan, there was some question as to whether they could survive long term.
While most Americans live blissfully in a man-made world, farmers still understand the blunt power of nature. The impact of this harsh winter will not be known till spring. Stay tuned for more reports in Midwest Wine Press.