Will Coffee Grounds Keep Slugs and Other Pests Away from My Garden? However, a word of caution about using coffee grounds in your garden in areas where you’re growing plants from seed: Some research has shown reduced seed germination and plant growth of many ornamental and edible plants when coffee grounds were used as a mulch or added directly to soil, says Chalker-Scott. That’s because the pH neutralizes as the grounds decompose, so you won’t have to worry that you’re going to throw off your garden’s soil pH off when using compost with coffee grounds.

But although the pH level of grounds ranges from mildly acidic to alkaline, they won’t make compost too acidic. Some gardeners wonder if the grounds can affect soil pH. This prevents the finely textured grounds from compacting and preventing air and water flow to the roots. If you try this, stick with a layer that’s not more than 1/2 inch thick, then cover it with a few inches of other organic mulch, such as wood chips, says Chalker-Scott. But you also can use spent grounds in small amounts as a thin mulch layer for outdoor plants. In general, only composted grounds should be worked into the soil as an amendment.

In addition, earthworms consume coffee grounds and pull them deep into the soil, so this may be why there’s improvement in soil structure after the application of grounds. They also contain small amounts of other primary nutrients such as phosphorous and potassium, as well as micronutrients such as calcium, magnesium, and copper. “Used coffee grounds contain nitrogen, so it’s a good addition to the compost pile.”Ĭoffee grounds have other benefits when added to compost. “Not everything contained in coffee beans makes it into the cup,” says Linda Chalker-Scott, PhD, professor and extension urban horticulturist at Washington State University. Adding used coffee grounds to your garden or compost pile is a great way to use something you’d otherwise toss.

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