While I still had some larger spent coffee grounds sources, I used a LOT of grounds in the garden. For a couple of years I was adding roughly 30-40 gallons of grounds a week. They were worked directly into beds, as top dressing, in compost, and even as top dressing in containers to deter squirrels. I also added them directly to worm bins. I had read the often recited comments about soil pH and tested frequently. I never saw any pH issues whatsoever. They smelled like coffee for about a week and then, no smell. The only time I remember offputting odors was when I didn't apply them as described above shortly after getting them. In the summer heat, it only takes a few days to mold when they're in closed containers. I just stayed ahead of it by applying them as I got them. I live in an urban area, very close to neighbors. My worms loved them as well.
Fast forward, I lost my coffee suppliers and no one close by saves them...even when asked...and even when that shop is a nationally known chain known for saving them for people.
I am still looking for a good source.
BTW, the only problem I ran into was really created by me. If you apply too heavily as a top dressing, it can crust up the soil surface. Time heals that and I stopped adding as heavily to surface applications.
One more caveat, DO NOT let your dogs near areas where you dumped coffee. Caffeine contains a lot of methylxanthine which can negatively affect brains and organs in dogs. My applications were in areas in which we highly controlled dog traffic.
