I would use products like bone meal, composted manures or bat guano on the hydrangea. Rock phosphate has high phosphorus but none to little nitrogen and phosphate. The others have some useful trace elements too. In areas where you have not planted anything yet or plan to use in the future, I would use rock phosphate. I am sure there are more products you can use out there.

I'd also attempt to bring the pH down a bit as well. Most hydrangea species would prefer a more acidic soil and definitely any of the bigleaf varieties. You could incorporate some peat moss into the planting area or amend with sulfur or any organic acid lovers fertilizer.

My two hydrangea petiolaris have been in the ground forfive years. heir color is good, they show lots of new spring growth, and seem to be thriving. Why no blossoms?

hardestree- better to start your own thread for responses.