Used coffee grounds are abundantly available for the asking at your local coffee shop. But just because the item is free, is it beneficial for composting?
Compost your coffee -
Coffee grounds add nitrogen to the compost, but as fertilizer they do not add nitrogen immediately to the soil. About 2% nitrogen by volume, used coffee grounds are a safe substitute for nitrogen-rich animal products. A study at Oregon State University showed that when composted, coffee helps sustain high temperatures in compost piles, in contrast with manure, which doesn't sustain the heat as long. When grounds made up 25 percent of the volume of a compost pile, temperatures stayed between 135 and 155 degrees Fahrenheit for at least two weeks. High composting temperatures help reduce potentially dangerous pathogens and kill seeds from weeds and vegetables that have been added to the compost. In the OSU study two weeks was sufficient time to kill a significant portion of both pathogens and seeds. When composting coffee, remember that grounds are considered green material, so balance your mix by adding an equal amount of brown material, like dried leaves, shredded cuttings, or paper.
Using coffee as mulch -
Fresh coffee grounds are acidic, but used coffee grounds are neutral when added to the soil. The acid in coffee beans is mostly water soluble, so it leaches into the coffee we drink. After brewing, the grounds are between 6.5 and 6.8 pH, so they won't affect the soil acidity. Coffee grounds can be used as mulch. Adding this organic matter to the soil improves drainage, water retention and aeration. Coffee grounds also help keep slugs and snails away from plants.
An additional benefit of composting grounds is diverting them from the landfill. And recycling coffee shop grounds fosters interactions between community residents and local businesses.
For more on composting, and the benefits of recycling coffee grounds see UCANR Master Gardener Tip Sheet, Composting is Good for Your Garden and the Environment, and the links used as reference, below:
Composting With Coffee Grounds – Used Coffee Grounds for Gardening, from gardeningkowhow.com
Coffee Grounds Perk Up Compost Pile with Nitrogen, from Oregon State University