We hear about adding coffee grounds to garden soil. What are the benefits?
Adding coffee grounds is a good way to add organic matter to your soil. You can work it into the soil before planting, you can spread it periodically on top, or you can add it to your compost bin, and treat it like any other compost when it decomposes. All three methods work fine. And all three strategies are fine, as for any compost, at any time of the year.
One caveat: while coffee is (obviously) acidic, coffee grounds are only mildly so. Adding them directly or as compost is NOT an effective way to acidify your soil--which means they are fine for your vegetable garden as well as around your landscape plants. But do not expect them to provide the very acidic conditions beloved by blueberry plants!
You can mix it into your existing soil or potting mix. Compost piles will be improved with the addition of coffee grounds. It improves the soil and encourages the growth of helpful microorganisms!
Here is an article that goes into all the details on how much and where to use coffee grounds in the garden.