You've enjoyed your daily cup. But can coffee grounds go in the ground?
http://www.pressofatlanticcity.com/113/story/381488.html
The Press of Atlantic City
Published: Friday, January 23, 2009

Question: I have access to large amounts of coffee grounds. Can I use it as mulch? Is it possible to apply too much?
Answer: The availability of large quantities of coffee grounds has increased with the emergence of so many coffee houses. Certain coffee houses allow you to set up a time to collect one day's or several days' worth, while others already have pre-bagged, used grounds you can pick up along with your latte. Keeping these grounds out of landfills is good for the environment. But are they good for your garden?

As a fertilizer, coffee grounds are a low-level source of nitrogen, having the equivalent of a fertilizer with the N-P-K numbers 2.0-0.3-0.2, as well as a minor source of calcium and magnesium. However, this only applies to composted coffee grounds. Researchers at Oregon State University say uncomposted coffee grounds are not a nitrogen source. When added directly to the soil, they can cause poor germination and stunted growth in seedlings. Composting is essential to maximize the benefits of adding coffee grounds.

To compost your grounds and their filters, just add them to an existing pile along with some leaves. If starting a new pile, layer one part leaves to one part fresh grass clippings and one part coffee grounds. Turn your pile once per week and it should be ready in six months. If the grounds are not used immediately, they may develop a mold. This is not a problem, as the molds will be consumed during the composting process.

When applied as mulch some problems may develop. Because of their fine grind, the grounds may pack down too tightly and promote fungal growth. There also is some debate regarding the acidity of coffee grounds. Some believe the grounds become neutral after they are brewed, while others believe the pH is too acidic for most plants.

Never use coffee grounds on potted plants because soluble salts can build up and injure the plants. Washington State Master Gardeners have also found fruit flies are attracted to coffee grounds, which is an additional reason not to apply them to indoor plants.
The short answer to your question would be that coffee grounds can be an excellent addition to the garden, but only after they are composted. In a compost pile they help to maintain high temperatures, which are necessary to kill weed seeds and pathogens. Once added to the soil they improve soil structure and attract earthworms. If you are adding them directly to your soil, wait a few months before planting and then test your soil's pH level.

Mona Bawgus is a certified master gardener and consumer horticulturist with Rutgers Cooperative Extension of Atlantic County. Write to her c/o Rutgers Cooperative Extension, 6260 Old Harding Highway, Mays Landing, N.J. 08330. E-mail:
bawgus_mona@aclink.org