Roses will uptake maximum nutrients when the soil pH is between 6.0 and 6.5. This reading changes in different locations of the garden. Other factors that change pH include use of chemical fertilizer and when the pH is tested, before, during or after the rainy season. West of the Cascades, the native soil tends to be acidic. (East of the Cascades the soil is alkaline) My Kitsap garden beds have had readings on October 2, 2016 between ph 4.5, pH 5.0 and pH 6.2. I applied granulated lime according to directions on the bag after these readings. You may have heard that lime is a slow acting soil amendment. I waited three months, until late December, to find pH in all rose beds to be pH 6.3 and pH 6.6.
I did not think this chart would project very well in the Rainier Room and even if it were projected, it seems to me to be something to study to fully understand.