Snow and Plants: How Much Insulation?

snow on sedum

Snow piles up on sedum.

After a winter that has featured an odd amount of rain, followed by very cold temperatures, we have finally gotten some snow. Several days of clippers dumping smaller amounts of snow — at my house in the 1 to 2 inch range for three days in a row — has resulted in some decent snow levels, finally. Folks in the far south central part of the state still have less than 4 inches of snow cover, but any points in the Twin Cities or northward are in the 8 inches and above range. If you live in the Arrowhead region, snow depth is more than 20 inches.

The question for gardeners is: Is this too little and is it too late to protect plants? The insulating benefits of snow are well-known, especially the fluffy kind of snow we have received recently, because the air is trapped in between the flakes. (For a complete discussion of snow, insulation and keeping zone-challenged plants going, I highly recommend you read the Pushing the Zone column by Rhonda Fleming Hayes in the March/April 2013 issue of Northern Gardener. It will be out in about three weeks.) Meanwhile, researchers at Rutgers University have found that 9 inches of snow makes about a 42 degree difference in the temperature at ground level. So, if it is -14 outside (as it was earlier this week) and you have 9 inches of snow, the ground temperature is about 28 — not bad for a hardy plant.

Unfortunately, when it was -14 here last week, my poor plants had little or no snow on them. Some have been mulched and that can prevent injury and all of my plants are USDA Zone 4 hardy or lower, so they should be able to take it. But, according to the U of M Extension Service, there may be some damage. The advantage of getting snow cover now is that when the temperatures start rising again, the ground will have snow to insulate it from frost heaving, which can damage roots.

Given how erratic temperatures have been this winter (and in the winter and hyper-early spring of 2011), I will probably add more winter mulch to my gardens next year. It seems we cannot depend on the snow to do that work for us.

—Mary Lahr Schier