People (smart people) have been using coffee grounds to enhance soil nutrition for centuries. Some even feed the grounds to their worms . . . the worms love it!
For those who don’t live in Starbuck-country, I’m sure any coffee shop will be happy to hand over their discarded coffee grounds. Perhaps by asking, you may convince them to offer the grounds to customers on a regular basis.
And by the way, here is a Sunset magazine article on how coffee grounds helps soil.