I have a beautiful patch vinca under an old silver maple. It gets no sun and probably not much to drink although I water enough in summer to keep the nearby oakleaf hydrangeas alive. My question really is about the Very thick layer of leaves that fall on the vinca. Do I leave it "as is" as mulch for over the winter? (Northern Maryland gets snow and weather in the teens for a week or two at a time.) When and how do I rake it off? I have tried raking in (soggy) spring and feel bad about all the vines I inadvertently rip out. So, what am I supposed to do about the piles of leaves.?
The leaves can protect the plants but too many may compact and rot the periwinkle. I'd rake early in spring before the periwinkle starts to bloom. However, I think in Maryland I would be tempted to remove the leaves now. Your cold and snow is short-lived so the periwinkle probably do not need extra protection. In my area, the snow and cold are for 4 months! A layer of leaves is helpful in THAT case!