Jane commented a couple of times on my instant compost post, wondering about adding coffee grounds to her compost pile. (Jane, by the way, has a great movie review site – check it out!) She had heard that they are too acidic and can wreak havoc in a garden. I figure if Jane’s asking, other people may be wondering, too, so I did a little digging.
Science Daily says:
Contrary to popular belief, coffee grounds are not acidic. After brewing, the grounds are close to pH neutral, between 6.5 and 6.8.
According to the article, coffee grounds are a high nitrogen material and can be added to the compost pile in lieu of manure. In fact, one interviewee claims that he had better success adding coffee grounds to his compost than with manure. As long as you’re maintaining a fairly equal balance of carbon (straw, leaves) and nitrogen (coffee grounds, lawn clippings, kitchen waste) your compost pile will just keep on doing it’s thing. The Science Daily folks even say it’s okay to put coffee grounds directly around plants, so long as you top the grounds with a layer of leaves or straw. It’s kind of like composting in place.
Sunset Magazine commissioned a study of Starbucks coffee grounds and found that not only are coffee grounds a good nitrogen addition to compost, they can be directly worked into the soil for improved soil structure and:
Use of the coffee grounds at the specified incorporation rates (rototilled into a 6- to 8-inch depth) will substantially improve availabilities of phosphorus, potassium, magnesium and copper and will probably negate the need for chemical sources of these plant essential elements.
I’ve always added my coffee grounds to the compost pile or tossed them directly on my lawn. I am far (far!) from scientific in my methods, but I can tell you that I’ve never had a problem that I connected to coffee grounds. In fact, I think it’s a good day to swing by the local coffee shop and see if I can collect some of their waste!