“It’s not the temperature” is a common Canadian phrase, followed by either “it’s the windchill” in the winter, or “it’s the humidity” in the summer. We Canadians tend to be very weather obsessed.
In this case, however, I am talking about why I cover the base (crown) of my roses in my gardens…
It’s not just the cold, although it is advisable to choose plants hardy to your area, that affects (kills) the roses. It’s the freeze and thaw cycles very common to Ontario weather that do them in. The mounded earth helps prevent the rose crowns from heaving out of the ground in these freeze/thaw cycles. Be sure to use clean soil for this purpose. I purchase plain garden soil in easy to manage bags to avoid introducing mold, mildew, bacteria or insects and their eggs to the roses.
I counted twenty-two rose crowns to cover in my own gardens, with lots more in my GARDENS4U gardens.