Janice Peterson: Snow plays critical role in protecting perennials
My husband showed me a report the other day on the relationship between snow cover and winterkill in alfalfa. Yes, the Peterson household is an exciting place to be in the wintertime! Alfalfa is a perennial crop plant, and this article made me wonder how our garden perennials will fare this spring after a very cold yet very snowy winter.
Perennial plants have unique ways to prepare for winter. As days become shorter, they make drastic changes to the water content inside their cells in preparation for the colder temperatures. The most important way plants protect themselves from freezing temperatures is to reduce the amount of water inside their cells. They also increase sugar and other compounds in the cell to lower its freezing point – essentially a sugary antifreeze!
If the root zones of plants are exposed to very cold temperatures the water inside the cells freeze and rupture the cell membrane, which then causes the cell contents to leak out when it thaws. You end up with a disgusting mushy mess (like putting celery into the freezer).
Snow is an excellent insulator, and snow cover is very important for perennial survival in Wisconsin. Soil temperatures fluctuate much less under snow cover. As little as 4” of snow cover can result in a 10 degree F increase in soil temperature. And when covered with snow plants experience more consistent temperatures and not the hourly ups and downs that create plant cell havoc.
The cycle of freezing and thawing can be very hard on perennials. Consistent snow cover throughout the entire winter season, as we have had this year, should help avoid plant death and frost heaving. Peg Reedy, agriculture agent for the University of Wisconsin-Extension Walworth Co. recently stated that “In January, measurements of soil temperatures at a 4-inch depth with a snow cover of 4 inches were still 28 to 30 degrees F”. This is amazing considering all of the nights (and days!) we've had this winter with air temperatures below zero F.
With all of the snow we've had this winter, I'm feeling very hopeful about my perennials, and can't wait to see what grows this spring! There will be a spring this year, won't there?