Roses really don't grow well on the California coast, at least the coastal locations I know well. When I lived in San Francisco, for example, I didn't know anyone who bothered to grow roses when other plants were so much more gratifying to grow. Most San Francisco gardeners concentrate on azaleas, rhododendrons, fuchsias, pelargoniums, and various bulbs.
I think the reason roses grow so well in the inland Calfornia regions like mine is that our nights are always comparatively cold. Even when the temperature soars into the 90s or into triple-digit territory, the nighttime temperatures dip down into the 40s and 50s.
This (hot days and cool nights) is often alleged to be a recipe for powdery mildew, but I have never seen powdery mildew on any roses other than OGR's in my garden. I have to assume that modern roses are resistant to it here. There is something else, though. I believe in overhead watering. It cleans the leaves, knocks off the aphids, and retards powdery mildew because the powdery variety of mildew can't grow on a wet surface. The roses in my garden that suffered from powdery mildew were huge ramblers that I couldn't possibly have watered from overhead without a helicopter. Dorothy Perkins was the worst, and I've replaced almost all of mine with Super Dorothy, which never gets powdery mildew.
David Austin actually produced a few roses that were never sold in England because they were more suited to the Northern California climate. The Endeavour is one of them.
