Q: I have heard that one can use coffee grounds to control slugs. I was wondering if there is any truth to this and what would be the process for applying the grounds.
A: Slugs probably won't like the coffee grounds, but I certainly don't have any problem with you trying it. Coffee grounds are a terrific organic fertilizer. Often the low pH is mentioned, but they also provide gentle low levels of N-P-K and many trace minerals. Even old coffee can be used as liquid fertilizer. I have used coffee as the only fertilizer for interior plants with great success.
Follow up: One Ground Crew reported great results using the coffee grounds to repel slugs. The slugs would come right up to it but wouldn't cross over the grounds.
Dilluted coffee is an excellent organt fertilizer, especially for orchids and African violets.
Coffee is food which is immediately available to the soil microbes. This means that it can be used directly on the ground as an organic fertilizer. The direct application rate is 10 - 20 pounds per 1,000 square feet. If you can get it in unlimited quantities for free, I'd tend to use it at 20 - 40 pounds per 1,000 sq. ft. More than that and you can smother grass but also stink up the neighborhood as it decomposes. Under plants you can use a heaping handful (or three) under each plant every month.
Coffee tends to get a green or blue-green fungus growing on it. The green one is really beneficial (Trichoderma species) while the blue-green one is modestly beneficial. In any case, moldy coffee is GREAT to use directly in the garden.