Oregon State University Extension Service

Coffee Grounds and Composting

Coffee grounds are a great addition to the garden and compost pile. Help to recycle this great organic resource and reduce the amount of organics going to the landfill!

Some information about coffee grounds

  • Coffee grounds are about 2% nitrogen by volume.
  • Grounds are not acidic; the acid in coffee is water-soluble so the acid is mostly in the coffee.
  • Coffee grounds are close to pH neutral (between 6.5 to 6.8 pH).
  • Coffee grounds improve soil tilth or structure.
  • Coffee grounds are an excellent nitrogen source for composting. They have a C/N ratio of 20-to-1. In informal trials with OSU/Lane County Extension Service, Compost Specialists recorded sustained temperatures of 140 to 160 degrees Fahrenheit for up to two weeks when coffee grounds were 25% of the material in the compost pile by volume.
  • Anecdotal evidence suggests coffee grounds repel slugs and snails in the garden.

How do I use coffee grounds?

  • Spread the coffee grounds directly on the soil. Cultivate into the soil. If left to dry out, they can repel water in much the same way as peat moss that becomes dry.
  • Spread on the soil and cover with leaves or compost or bark mulch.
  • Add to the compost pile by layering the ingredients using 1/3 leaves, 1/3 fresh grass clippings, and 1/3 coffee grounds.
  • Add coffee grounds as part of a static compost pile, being sure to always add an equivalent amount of a carbon source such as shredded paper or dry leaves. Mix together well.
  • Coffee grounds are not a nitrogen fertilizer. In a germination test at the GrassRoots Garden in Eugene, OR, coffee grounds were mixed with potting soil at a ratio of 25% by volume. Lettuce seeds showed poor rates of germination and stunted growth compared to lettuce seeds planted in potting mix without coffee grounds.
  • If you are incorporating coffee grounds directly into the soil, add a nitrogen fertilizer at the same time. Coffee grounds encourage the growth of microorganisms in the soil, which use nitrogen for their growth and reproduction. While the coffee grounds are being broken down by the microorganisms, the additional nitrogen in the fertilizer will provide a source of nutrients for your plants.
  • Add paper coffee filters to the compost pile as a carbon source. Tear them into small pieces to speed decomposition.
  • Coffee grounds do not “go bad." For future use, store in a 32-gallon trash container near the compost bin or pile.

General composting tips

Source URL: https://extension.oregonstate.edu/gardening/soil-compost/coffee-grounds-composting