Thank you for your question, Louise. I found some interesting articles for you to read. Like most everything in life it seems the answer to your question is, “it depends.”

Below are three links to short and informative articles about using coffee grounds in the garden:

Penn State Extension Philadelphia Master Gardeners : Recycling Coffee Grounds in the Garden (philadelphiacountymastergardeners.blogspot.com)

Gardening on a Shoestring | Illinois Extension | UIUC

Using Coffee Grounds in the Garden | Cooperative Extension | The University of Arizona

The last article, from the University of Arizona contains the following quote, which nicely sums up the topic:

“Dr. Chalker-Scott has synthesized coffee ground research results to make the following recommendations. In compost, limit coffee ground content to no more than 20% of the total compost volume – more than 30% has often been detrimental. Additions of diverse raw materials to compost should ensure a diversity of microorganisms. Don’t assume coffee grounds will make an acidic compost; pH levels will fluctuate over time.

In mulch, since coffee grounds are finely textured and easily compacted, they can create a barrier to moisture and air movement, especially when applied in thick layers. Dr. Chalker-Scott recommends against using pure coffee grounds as mulch. Instead, try using a thin layer (no more than half an inch) of coffee grounds and cover with a thicker (four inches) layer of coarse organic mulch like wood chips.”

In other words, go ahead and compost your coffee grounds, but don’t go overboard. If you have a morning cuppa joe (or two), by all means, compost your grounds. However, if you run a coffee shop and bring home many pounds of grounds, use some and share most. Moderation is the key.

Happy New Year and Happy Growing!