One week ago today, here in Minneapolis, we woke up to temperatures of -20 F (-29 C), with wind chills around -35 F (-37 C). And we had upwards of a foot of fluffy snow, which was blowing and drifting in the wind. Now, lest you dismiss this as being normal for Minnesota, in the third week of December, you are mistaken; it is not! This was the Polar Vortex, that shifting of super-cold air from around the north pole, pushed southward, with the jet-stream, by temperatures in the Arctic Circle, which have been hovering right around freezing for several weeks, a departure from normal polar temps of -25 to -35 F. (-32 to -37 C). In other words, as counterintuitive as it may seem, the shift of the polar vortex southward into North America and Siberia is the effect of global warming in the polar region. See my December 2016 blog:
Now, on Christmas day (and for the last several days), with the Polar Vortex past, we are experiencing unusually warm temperatures for late-December and our once-fluffy snow is melting fast. Right now, at noon, I am looking out my window at wind-blown steady rain, with the air temperature hovering just above freezing. Thunderstorms and temperatures in the 40s are predicted for later in the day, with upwards to an inch of rain, and it's likely that most of our snow cover will be gone by tomorrow.
Thunderstorms on Christmas Day in Minnesota? No one can remember this happening before, but it serves as a very good example of what winter-protecting your roses is all about, if you live some place where winter (and especially the Polar Vortex these days) affects your garden. Last week at this time, my roses were frozen solid, probably at least a foot or more below the surface (it doesn't take long for that to happen at -20 F (-29 C). Now, with temperatures well above freezing and rain coming down, the ground surface will start to thaw after the snow melts, but I know my roses will stay frozen solid because they are mounded with dirt and insulated with leaves and/or marsh hay. Likewise, tomorrow morning, when temperatures fall and the surface re-freezes, they will be unaffected, because they did not thaw.
Now, for example, if you live near St. Louis, Detroit, Indianapolis, Louisville, Boston or New York, and your ground and roses were certainly not frozen before the Polar Vortex came through last week, but you had at least mounded them and your bud unions are planted several inches below the ground, it is very unlikely that they froze from that short blast of polar temperatures (which we may see again in January or February). So, like mine, they are just fine for exactly the same reason: they were winter-protected from freezing and thawing. The only difference is that mine didn't thaw and yours didn't freeze; so no problem either way. If you haven't already seen it, please read my recent blog: "Five Important Steps to Winter-Protecting Your Roses". Here is that address:
As I have said repeatedly in the last few years, you can debate why global warming is happening but the facts clearly demonstrate that it is; the Polar Vortex notwithstanding. As mentioned earlier, the Polar Vortex is caused by extreme warming of the polar regions pushing cold air southward into Siberia or North America (or both this year), via the jet-stream. And because it is still unusually warm in the Arctic, we can expect the Polar Vortex to re-emerge in any winter going forward, particularly in January or February (December was a surprise). Please see my March 2014 blog "What the Heck Was Wrong with this Winter":
as well as my October 2014 blog: "Winter-Protecting Roses in a Climate-Change Environment".
Bottom line? If you live in any zone where winter comes along at some point each year, do something to winter-protect your roses, even if it's only planting your bud unions several inches below ground and providing some mounding with mulch or dirt around your plants each fall, because we can now say, with a fairly high degree of certainty, that the Polar Vortex will strike again in North America, in any year going forward.