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Aug 16, 2013 5:32 PM CST
| It's six hours per day.
It doesn't matter if the skies are overcast as long as the plants are not planted in shade, if you select the kind of rose that will work in that kind of light. Roses have several bloom forms defined by the number of petals in the bloom. When most people think of roses, they think of the hybrid tea rose form, but there are some real beauties that do not look like hybrid teas and will perform better in your conditions because they often have fewer petals and open well with less intense light.
Almost any rose with fewer petals and light colored will open well without intense sunlight. In fact, they will do better because they are less likely to be "fried". Roses with a single, semi-double and double bloom form are the most shade tolerant, but that is a generality.
The rose class called 'hybrid musks' are generally considered to be shade tolerant. That does not mean that they will do well in a shade garden, but that they can handle the low light conditions you have described quite well. Joseph Pemberton is supposed to have been the originator of of this class of roses and and he bred roses in England ... low light conditions, from what I have read.
Here's a link to his breeder page on HMF...
You can click on the PLANTS BRED to get a list of live links to the roses he introduced.
But you are not limited to this class. There are single, semi-double and double roses in several rose classes that will open well in your less intense sunlight.
As for disease resistance, I honestly believe you have to find out that information from people growing roses in your own climate. I explained the reason why I can't help you find the best disease resistant roses in response to Bonehead's query on the Rose Forum:
(The post is to long to repeat here).