Caffeinating the Garden: Use Caution with Coffee in the Garden

Help for the Gardener from the
Contra Costa Master Gardeners' Help Desk

Description of Client's Question:

A client wrote in saying that he had read some advice about using coffee grounds as a fertilizer. The advice apparently also noted that coffee grounds would be a deterrent to gophers and moles. About two years ago, the client applied about 500 pounds of coffee grounds in a small area, but stopped when his lawn and some native plants started to die. (But the client did note that the coffee grounds got rid of the gophers!).

The client said that even after he ceased using coffee grounds, the plants have not recovered and the lawn still looks dead. He thought that perhaps the soil had become too acidic and perhaps gypsum could be added to remedy the problem.

Here's the advice that Master Gardeners gave the client:

Soil acidity isn't the reason why nothing is able to grow in the areas where you applied coffee grounds, nitrogen depletion is. In fact, coffee grounds don't cause soils to become acidic. The acidity in coffee is water soluble and the acidity in the beans ends up in the coffee when the ground beans are brewed.

Oregon State University recently conducted a study on garden use of coffee grounds (http://extension.oregonstate.edu/lane/sites/default/files/documents/cffee07.pdf ). OSU found that large amounts of coffee grounds stimulate the development of soil microorganisms which in turn use the nitrogen in your soil to process the coffee grounds. The study also states that acidity of the resulting soil is not the major issue, but nitrogen depletion of the soil is a major concern.

I would try using a good organic nitrogen fertilizer and applying it to the area where growth has ceased. The organic fertilizers are slow release and will not burn your lawn or surrounding plants. It may take repeated applications over time to adjust the soil composition. If you have bare ground that is affected, you could also try covering the area with compost or leaves and let the natural composting process help to balance your soil.

Editor's Note: Each month the CCMG Help Desk's Quality Assurance Team selects responses to county residents' Help Desk questions that produced informative responses that are either unique or unusual, or provided updated information that would be informative to all gardeners, or are of general interest, especially of seasonal concerns. We are highlighting these responses in the HortCOCO blog so all interested Master Gardeners and the public may utilize the information.

The CCMG Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523.  We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, and we are on the web at http://ccmg.ucanr.edu/

Read more