If, like me, you make a daily pot of coffee (or two), you have a fabulous source of organic matter right at your fingertips. In compost jargon, coffee grounds are a "green" item, meaning an item that is rich in nitrogen (yes, I know coffee grounds are brown. But in terms of your compost pile you must be a bit color blind! In the compost, they're green. Trust me.) Coffee grounds are approximately 1.5% nitrogen. They also contain assorted amounts of magnesium, calcium, potassium, and other trace minerals.
I have been using coffee grounds in the vegetable garden for years, believing from hearsay and my grandmother that this evidence of my daily coffee habit could be good for the garden. A family of Starbucks fanatics, my clan takes the coffee company up on their offer of free Starbucks “Grounds for Your Garden” in addition to adding more from her own home brew.
At my own home, I make a lot (and I do mean a LOT) of coffee. Most of it ends up in the garden somehow. The vast majority goes into my compost pile, but I do sometimes deposit grounds directly into the garden, or swish the grounds around with some water and pour the slurry into the soil like compost tea.
There are a few things to keep in mind when using coffee grounds. Don’t just dump coffee grounds on top of the soil or mulch. The dried grounds can wick moisture away from soil and plants. Instead, mix the grounds into garden soil first and then put them onto the compost pile. I went looking for other online info on coffee grounds and I found a great study conducted at Oregon State University Extension Service that you might find interesting, too. (Of course it would be from the Pacific Northwest, the regional capital of coffee!) The report dispels the myth that the grounds are acidic (they are actually closer to pH neutral) but it confirms that they do contribute nitrogen to compost and to the soil when used in tandem with a fertilizer that contains some nitrogen. Coffee grounds also improve soil tilth (the physical condition of soil) and soil structure, and they may repel slugs and snails, as well. Read more of this OSU study to learn how and when you should use coffee grounds in your garden. It turns out that both my grandma and Starbucks were right. Coffee is good for your garden. So drink up!