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GroEdibles Blog

May 2

Coffee, Coffee Everywhere on Abbot Kinney…but How Much Mulch is too Mulch in the Garden?

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With dozens of places to get a fine cup ‘o Joe on our block, you might think we’d be collecting the grounds by the truckload to use at The Cook’s Garden. But this is the time for restraint and solid information. Whenever you think about amending your soil with an organic, please take some time to fully investigate what effect that substance (and the amount you’re adding) will have, short and long term, on your soil chemistry.  A reminder: test your soil regularly (pH and fertility) to see if any deficiencies have developed so that you can amend to correct efficiently without potentially causing additional problems.

As I always advise, when you’re doing Internet research, seek out resources that are researched-based (i.e. major universities with Ag / Horticulture Departments with Cooperative Extensions). When you type in your Internet keyword search always add the words “cooperative extension”. This search will give you sites only from universities’ cooperative extensions. You can also limit your search geographically by adding your state or region/county.

Though we’ve always used coffee grounds as a component of our green composting and vermicomposting programs, I’ve not used it as direct mulch in the garden since balance in our biosphere is key. By adding correctly proportioned amounts of grounds in our compost recipe, that valuable component gets into to our soil every time we amend (we use compost as a mulch) so there is no need for additional amounts of grounds. We’re careful not to over-do anything.

I’ve been asked several times recently by clients and customers the question about using grounds essentially as mulch or amendment so I thought it would be helpful to post the horticulture recommendations. I’m including two articles, one from Professor Linda Chalker-Scott (an academic I reference often), Master Gardener, WSU editor, Extension Urban Horticulturist and Associate Professor, Puyallup Research and Extension Center, Washington State University as well as a guide to using coffee grounds from Oregon State University Extension Service.

Both resources shed some light on and debunk some homespun myths about coffee grounds – its acidity and its nitrogen content among others. Dr. Chalker-Scott also talks about what nutrients coffee grounds can actually deliver and how, as well as recommendations on how much to use. In essence, you’ll get an extra bang for your six buck coffee cup by using the great grounds in your compost and as an amendment, just be aware of when enough is enough.

WSU Coffee Grounds



OSU Coffee Grounds



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