Photo courtesy of How can I recycle this at Flickr.com.
While coffee grounds usually compost just fine, you need to be careful about how much of them you add to your compost heap. Coffee and similar beverages (including non-herbal teas) tend to be somewhat acidic, with coffee grounds from dark roast checking in with a pH of about 5.0 (7.0 is neutral). Other grounds may be significantly less acidic, especially if the water you use to brew your coffee is already slightly alkaline.
A good rule of thumb is to make sure that coffee grounds comprise no more than 25% of your compost; this should be no problem for most households. If you’re concerned about the coffee-generated acid content in your compost, you can offset it by mixing in finely-ground eggshells. Eggshells are high in calcium carbonate, which is mildly basic.
Alternately, your acidic compost is just fine if you plan to use it exclusively on acid-loving plants like azaleas and blueberries. And here’s more good news: earthworms seem to like their java as much as any of us. Anecdotal evidence indicates that they’re attracted to coffee grounds, so they might have a place in your vermicomposting bin.
Photo courtesy of jonny.hunter at Flickr.com.
If you prefer to segregate out your coffee grounds, they do make a good soil conditioner—again, especially if your soil is naturally basic—and will add a significant amount of nitrogen, too.
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