Coffee grounds can be an excellent addition to a compost pile. The grounds are relatively rich in nitrogen, providing bacteria the energy they need to turn organic matter into compost.

About 2% nitrogen by volume, used coffee grounds can be a safe vegan-friendly substitute for nitrogen-rich manure in the compost pile, explained Cindy Wise, coordinator of the compost specialist program at the Lane County office of the Oregon State University Extension Service. “A lot of people don’t want to use manure because of concerns about pathogens,” said Wise.

Contrary to popular belief, coffee grounds are not acidic. After brewing, the grounds are close to pH neutral, between 6.5 and 6.8. The acid in the beans is mostly water-soluble, so it leaches into the coffee we drink.

“Recycling this valuable soil amendment and compost ingredient makes sense both economically and environmentally,” she said. Wise is encouraging gardeners and those that compost in other communities to arrange to collect coffee shop grounds for composting. But be sure to make prior arrangements with a coffee shop to collect grounds. Then, take a clean five-gallon bucket with a lid, label it with your name and telephone number on the bucket and lid and leave it at the shop and then pick it up at the shop’s convenience.

Add grounds to your compost pile by layering one part leaves, to one part fresh grass clippings, to one part coffee grounds by volume. Turn once a week. This will be ready in three to six months. Alternatively you can put them in an existing unturned pile. Just make sure to add a high carbon source, such as leaves to balance it.

Grounds may be stored for future use. They may develop molds but these appear to be consumed during the composting process; your paper coffee filters may be composted along with the grounds.

Keep in mind that uncomposted coffee grounds are NOT a nitrogen fertilizer. Coffee grounds have a carbon-to-nitrogen ration of about 20 to 1, in the same range as animal manure. Germination tests in Eugene showed that uncomposted coffee grounds, added to soil as about one-fourth the volume, showed poor germination and stunted growth in lettuce seed. Therefore, they need to be composted before using near plants.

Coffee grounds help to sustain high temperatures in compost piles, which is a good thing. Elevated temperatures reduce potentially dangerous pathogens and kill seeds from weeds and vegetables that were added to the piles. In addition to this, coffee grounds seem to improve soil structure, which attract earthworms. In contrast, the manure in the trials didn’t sustain the heat as long.

“An additional benefit of diverting coffee grounds from the landfill is that it helps cut greenhouse gas emissions. Keeping organic material out of the landfill is a good thing for reducing greenhouse gas emissions, because as these materials decompose, they produce methane, which is about 25 times as bad as carbon dioxide, a greenhouse gas,” said Dan Hurley, waste management engineer for Lane County’s Short Mountain Landfill.

Recycling coffee shop grounds also fosters interactions between community residents and local businesses. The coffee grounds stay in their communities, meaning that fuel isn’t being used to truck them from far-flung areas of the county to landfills.

-Reprinted from Science Daily using research from Oregon State University. (2008, July 10). Coffee Grounds Perk Up Compost Pile With Nitrogen.