I think it has to matter to us in warm-winter zones. I’m in 9a, inland SoCal, and like many people here have deciduous shade trees in my backyard. When those leaves are gone, roses do grow, especially in winter rains if we get them — but I never plant or keep roses right under the trees.

The PNW, of course, is a different kettle of ... salmon. Wouldn’t length and intensity of sunlight factor into the sun-shade equation?

It’s an interesting question. I hope you get more knowledgeable answers!

I've never heard or seen anything about this before. I can't imagine why the sun would be a problem in the winter for anyone really but the further South and the warmer the climate the more problem with too much sun there might be. The more North you are the less problem. If your roses are going fully dormant in the winter then too much sun exposure shouldn't be a problem. For one thing the daylight hours are much shorter, everywhere, and for another the angle of the sun is much lower the further North you are. So it is filtered through much more atmosphere and is weaker.

Exactly, seil. Here in Idaho, photosynthesis ceases around Nov 7, due to the angle and weakness of the sun. Diane

At the opposite extreme, I have had multiple roses die in winter-shaded areas as they get much colder than those in the sun. A little winter shade hasn't hurt, but alot has in my yard. I've since moved them all where they get more sun year round.

Vap, that makes sense! I didn’t think my plants would get too much sun, I just honestly didn’t think it would matter if they got any since they were asleep anyway.

But staying too cold for too long makes sense. I’m so happy to have this solved...it really did baffle me why sun in winter mattered!