Feel Good about Composting Used Coffee Grounds
I'm in love with coffee, and I was surprised to read that the use of coffee grounds in gardens gets mixed reviews. Some gardeners contend they are too acidic and harmful to plants. Others love the access to free coffee grounds from coffee shops and celebrate the positive results of incorporating the grounds into their gardening. I have been adding coffee grounds to my compost for several years so after reading the contrasting views, I felt the need to do some research.
While exploring the topic, I found an article from Oregon State University that addressed all of my questions. It seems the nitrogen rich nature of coffee grounds makes them an excellent substitute to manure in your compost bin. It is pathogen free and provides enough nitrogen to feed bacteria to break down the organic material in the compost. Coffee is considered green material in your compost so you will need to balance it with an brown material like grass clippings or leaves.
In addition to being a nitrogen rich addition to your compost pile, the researchers from Oregon State University found that if 25% of your compost is made up of coffee grounds, the temperatures of the pile will stay higher for longer periods of time. This helps to kill pathogens as well as weeds and other unwanted seeds. The coffee grounds also appeared to improve the soil quality and attract earthworms.
Many articles I read indicated it is bad to use coffee grounds directly on plants due to its acidic nature. This article actually claims used coffee grounds are almost pH neutral. However, they do recommend using only composted coffee grounds around plants. According to their research, applying fresh coffee grounds around plants directly may stunt growth and stop germination of some seeds. They did indicate coffee grounds can be added to the soil directly, but only after they have been allowed a few months to break down.
Overall, coffee grounds seem to be an excellent addition to your compost, but it may not be the best idea to add them directly to your garden. Using brewed coffee grounds from your own home or taking advantage of free coffee grounds that many coffee shops give away helps to keep waste out of landfills. This in turn reduces greenhouse gases. So, feel good about composting your coffee. In most cases the filter can be added to your bin as well. Your garden will benefit and so will the earth.