Here is what a rhododendron nursery in Oregon does:

Van Veen Nursery in Portland, Oregon, reported after using coffee grinds from Starbucks Coffee House for about 18 months that they were very satisfied with the results. 1) it helps to aerate their clay soil. 2) slugs don't like to go through. (So you can see they have both mixed in and put on top.) It does help to make the soil more acidic. But it does not replace fertilizer.

They suspect that by making the soil more acidic you are actually helping the uptake of magnesium. This in turn helps iron uptake and that helps to make the plant green. So really you are starting a process not fertilizing. Combine the coffee with horse mature and organic mulch and watch the amount of fertilizer you use decrease dramatically. As for how they apply it, when the plant is dry and just before it rains they sprinkle it on and around. The rain takes it from there. Otherwise they incorporate into the new beds. No exact rate just cover the top and work it in. (Courtesy of Vicki at Van Veen Nursery)

Thanks, rhodyman, that is good information. I know that rhododendrons & azaleas like an acidic soil. I'm going to give it a try. We have clay soil due to the builder removing part of a hill to build our house. So anything that helps aerate it is great. Now if it would just keep down the weeds!
Thanks!

My DH has been picking up the grounds for over a year now----The worms love it which helps the clay soil.

I still feed my roses alfalfa.

Florence