How Much & How Often Do I Fertilize With Coffee Grounds?

Misconception About Acidity

• A lot of gardeners think that coffee grounds are acidic and should only be applied to acid-loving plants. But that is a common misconception, OSU says. Water leaches most of the acid out of coffee grounds. After use, grounds have a slightly acidic pH of 6.5 to 6.8, which is close to the neutral level of 7. Substances that have a pH of more than 7 are alkaline.

  OSU notes that coffee grounds improve the loaminess of soil. They attract earthworms, which love grit, prefer a neutral pH and help mix the grounds into the soil.

Decomposition Methods

• Putting plants or seeds in soil containing grounds that haven't yet decomposed can stunt germination and growth, according to OSU composting research. Three decomposition methods the university suggests include composting coffee grounds, digging them directly into garden soil and combining them with leaf mulch on top of the soil.

Making and Applying Coffee Compost

• Coffee grounds can be added to a compost heap containing plenty of carbon-rich matter, such as dried leaves, and nitrogen-rich waste including vegetable scraps, grass clippings and other yard waste. These ingredients are layered in thirds with equal amounts of grounds, leaves and green waste. The amount of coffee grounds produced by one household isn't likely to be enough for this recipe. To obtain extra, visit local coffee shops to request used grounds.

  Compost is ready to add to soil when it looks dark and crumbly. Work an inch of the coffee compost into the entire garden in the fall and in the spring before planting. If the amount is limited, dig a cupful into the soil around each plant. This is called "side dressing" and can be done a few times during the growing season.

Other Decomposition and Application Methods

• Coffee grounds can also be dug directly into garden soil before the planting season, but will consume nitrogen in the process of decaying and need a few months to break down. It is wise to add extra nitrogen to activate decomposition of the grounds and avoid depleting the nutrient.

  A third decomposition method involves placing a 1/2-inch layer of coffee grounds on top of the soil, covering it with a layer of dried leaves and keeping the mulch moist. This combination acts like a slow-release fertilizer during the growing season. OSU says not to place grounds alone on top of the soil, because they form a crust, repelling water and restricting air from plant roots.