I have the fertilizer for the blueberries we're about to plant but I didn't want to go too acidic - it was sort of a wait-and-see-if-this-makes-a-difference kind of thing. I'd also heard it was easy to burn non-dormant plants with the acid fertilizer and the coffee wouldn't be able to work as fast and so was likely gentler. From what I read, it sounds like spent coffee has a neutral PH, which is why we did fresh grounds.