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Coffee grounds

CHS / Herald

Q & A on the uses of coffee grounds as compost.

June 29, 2005

Most Calgary gardens will benefit from the addition of used coffee grounds, or more specifically, it is the soil that will benefit and subsequently the plants that grow in that soil. We have alkaline soils here as a consequence of the chemical characteristics of the water that for thousands of years has flowed into the Calgary region from our Rockies. We know that our water is “hard” … that reflects the lime content of our water, and serves as a reminder of the alkaline nature of the water. The treated water that the City of Calgary provides has a pH of between 7.2 and 8.3 (pH 7 is neutral) and our soil typically has a pH of 8 or more whereas most perennials like a pH of between 6 and 7.5 Many nutrients needed by plants are absorbed by the plant when the water is more or less neutral in pH, so anything you can do to slightly increase the acidity of the water on your garden is beneficial: rain water, for instance, is slightly acidic, so it’s use helps too. Used coffee grounds typically have a pH of between 5.5 and 6.0, i.e., they are acidic, as too, are tea leaves. Some plants thrive on acidic soils.


Coffee, when spread thinly on top of or mixed in with the topsoil, will help amend the soil in several ways. First of all we are adding organic matter, which clayey or sandy soils can benefit from. Coffee is high in nitrogen content (the N in NPK listings of fertilizers containers): the nitrogen helps green - up plants. If we use coarse coffee grounds, we allow air and water into clayey soils which is good, and earthworms find them easy to burrow into, and they bring their own benefits to the garden. Coffee grounds retain moisture, suppress weeds and are “eco-friendly”.


Coffee grounds can be added into your composter, but beware, they are “greens” from the composting perspective because of their high N2 content, not “browns” such as fall leaves. The paper filters that can come with coffee can be a nuisance as they are slow to disintegrate and if you leave them in the ground over winter, they will slow down the thawing progress, and tend to generate molds.


Some small coffee shops can be persuaded to keep the used grounds for you, and Starbucks have their own program for giving grounds away: a year-round possibility for reducing waste collection!


Check out this site: http://www.starbucks.com/aboutus/compost.asp


Glynn Wright