Coffee Grounds and Your Garden
You may have heard that used coffee grounds can be used as fertilizer in your soil. But can they really? Here are a few things to consider before you add coffee grounds to your soil.
Coffee Grounds in Soil
Because coffee grounds contain a lot of nitrogen, people say they are great to mix into your soil to act as a fertilizer. Plus, in general, adding organic material to your soil is helpful for improving the nutrient content.
The issue with coffee grounds is that even though they are rich in nitrogen, they are high in acidity and caffeine. Thus, some recommend them only as an additive to soil for acid friendly plants (ex: blueberries, holly, azaleas, Japanese iris). Yet, the real issue is the caffeine content and texture of coffee grounds. Over many years, caffeine naturally developed in a few plants, because caffeine inhibits the growth of other plants around them. And studies have shown this also happens when coffee grounds are added to the soil.
The fine texture of coffee grounds also causes it to clump (much like clay) which can inhibit root development if you add too much. Yet these two properties of coffee grounds (caffeine and texture) do lend to it being a fine addition to your mulch.
Coffee Grounds as Mulch
Dumping lots of coffee grounds on the surface of your soil as mulch will have negative effects, preventing good water absorption as it clumps, and contributing to caffeine absorption in the plants you’re trying to protect.
Good mulch on the other hand, provides a cover for soil that helps keep weeds at bay, and protects the soil from direct impact from the elements.
To use coffee grounds in mulch, mix it with other organic matter and rake it into the very top layer of soil to prevent it from clumping. This keeps the caffeine at the surface level away from established plants roots, yet still acting as a barrier to the elements.
Coffee grounds can be a great addition to your mulch but they are not a magic trick for healthier and more vibrant gardens. It’s great to recycle waste when we can, but if you drink tons of coffee, the grounds might find better use elsewhere.