Coffee is a daily staple for countless people around the world. Coffee may also be good for countless plants in gardens around the world. While few people will brew a special pot just for their roses, many people could benefit by recycling their used coffee grounds into the compost or spreading them out in select places in the garden.
Coffee grounds contain roughly 2 percent nitrogen by volume. The greatest percentage of nitrogen in coffee grounds is not in a form that plants can use immediately. Microorganisms in the soil break down the nitrogen and release it in a form that plants can absorb and use for their growth. The potassium and magnesium in coffee grounds are readily available to the plants in high enough concentrations to promote growth.
"Sunset" magazine conducted a study and found that coffee grounds come in at about 6.2 on the pH scale, which makes them slightly acidic. Other institutions, such as the Oregon State University Extension, have concluded that coffee grounds are a little less acidic and closer to neutral, with values between 6.5 and 6.8. Gardeners are interested in these pH values because some plants have specific pH requirements to help them to absorb nutrients from the soil. You can change the chemical balance of the soil within a growing season, contingent upon factors such as soil composition and rainfall, among others.
Use coffee grounds as a soil amendment to improve the structure of all types of soil. Earthworms consume the coffee grounds and deposit them along the paths that they create in the soil. The actions of the microorganisms, bacteria and fungi that feed upon the coffee grounds also contribute to an improved structure. Good soil structure means that water, air and nutrients are present in the soil, and the plant is able to use those elements effectively.
Coffee grounds provide the greatest benefit to the garden as a compost additive. Once the grounds are composted, gardeners may use them throughout the garden. Coffee grounds have a high carbon-to-nitrogen ratio, similar to grass clippings or animal manure, which measure close to 20-to-1. Therefore, despite the brown appearance of coffee grounds, they are an excellent source of green materials for your compost. Coffee grounds may help the compost heap to reach higher internal temperatures and increase the overall efficiency of the decomposition process.