This may not provide direct answers to your questions, but have you considered the addition of worm castings to your soil? I'm squeamish, so I can't imagine handling a thousand worms, but this year I bought a bag of worm castings from Amazon and applied them to the roses in three of my rose beds. I just poured out about half a cup of castings around the perimeter of each rose bush in those beds and watered them in. I didn't bother to dig them into the soil. The instructions might as well have said "Apply and stand back!" The roses in those beds took off like crazy. They have exhibited vigorous growth, quicker reblooming, and visible improvement in general health. Some of the old rose bushes in those beds that have been dwindling in size in recent years are suddenly producing new basal shoots.
