Effects of fertilizers on bloom color and health of plants
2011 & 2012 were dry summers in my Chicagoland. My water-bill was doubled, but my roses were stingy, some Austins didn't bloom. I gave them tons of tap water, hard-well water at pH 8.
2013 summer I watered much less, but fixed my tap water with sulfate of potash & gypsum & molasses. Got over 40+ blooms on many roses, even for 90+ degree days.
2014 we had a cold & drier spring, I used sulfate of potash with chicken manure. Got 70+ blooms on Frederic Mistral, but blooms were washed out to white and deformed. So I threw gritty lime stones, plus red-lava rocks. Blooms became well-formed, and darker pink. I realize that sulfate of potash promotes MORE blooms, but I need calcium for better-bloom-formation, and trace elements in molasses or red-lava-rocks for better bloom color. See below for Frederic Mistral's cluster, after lime-application, but before red-lava.