“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 temperature (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 (I purchase plain garden soil in easy to manage bags for this purpose) 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, lots more in my client’s….
It goes the other way too. There are only two cultivars of apple that grow with minimal chill in Beverly Hills, and neither of them is very good. One would think that anyone could grow apples! I would rather take a little bit of chill than do without apples, pears, and what needs a chill. However, I will gladly pass on the peonies than deal with the sort of chill that most people on the continent get! (Only some of grow peonies, but they are not as happy here as they are in Oregon or farther north.)