A friend of mine says that you can just toss coffee grounds out onto the soil as a way of composting but I am not so sure about this. I thought coffee was very acidic, will that not harm my plants? can they absorb the coffee through their roots?

I've gotten bagsful of coffee grounds from coffee shops and added them to both soil and compost.

For soil, I found that the grounds will dry into a water-repellent crust if they are placed too thickly, say half an inch. To prevent that, just mix them with soil or cover them with mulch, and rake it all around a bit so that the grounds are not a separate layer.

For compost, many of the grounds I got were in lumps. I found that if I did not break down the lumps when I added them to compost, the lumps were still there a month or so later when it came time to sift the compost. So I placed a plastic nursery flat with small holes on the surface of the compost and crushed the lumps through the holes as I added them.

Coffee grounds can most certainly be added to your compost and also directly to your soil. Instead of simply tossing them out though, you may wish to incorporate them a bit more thoroughly by digging them in.

Much to my amusement, I found an article from Sunset magazine where they actually sent a sample of Starbucks coffee grounds for a soil analysis and found that it was rich in nitrogen, phosphorous and potassium and all of these elements were present in a form that are easily taken up by your plants. You are also correct that coffee is acidic. Fortunately, by the time the grounds get to your soil, brewing in water has removed most of the acidity. The pH of the grounds tested was 6.2. You can read the article here:

http://www.sunset.com/garden/earth-fr...

I am merely an amateur gardener but I can tell you that after hearing the same thing you did I added coffee grounds several times to my tomatoes last year and they thrived just as much as they do every year. It's only anecdotal evidence as I lack the scientific knowledge of plants that Lindsay clearly has, but I hope it helps a bit :)

I'm growing on a very beige sandy soil. I enjoy putting the coffee grounds directly on top finely spread so I can pretend I have a nice deep dark loam.

Day dreaming aside I have added about 400 lbs of coffee grounds to my backyard Starbucks giant silver grounds bags weigh maybe 10 pounds dryish each. That being said it is an organic matter and will assist in buffering soil pH. Bring low (acidic, sour) pH up and high (alkaline, sweet) pH down.

I have concentrated grounds around my garlic to mulch them and have found no discoloration associated with the ground or difference in flavor. Same can't be said about a bare hand spreading used coffee grounds though. When saving the coffee ground my work produces I compost them to break down the coffee filters, my wife didn't appreciate them blowing all around the yard.

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