Coffee grounds are a powder created from roasted coffee beans. While commonly enjoyed as a beverage, very few people are aware of their added benefit in the garden. Whether planting roses or invigorating a citrus tree, coffee makes an excellent addition to the compost pile.
Coffee is a natural substance, which means it adds nutrients to gardens without any harmful chemical effects. Coffee adds acidity to the soil, which is necessary for acidic soil-loving plants such as citrus, blueberries, avocados, roses or azaleas. Using coffee in the garden will also reduce the amount of waste being sent to landfills, as even used coffee grounds can be added to compost piles along with their filter.
Coffee is a natural fertilizer, which means it takes longer to break down than chemical fertilizers. In warmer months, coffee releases some of its nutrients directly into the soil quickly, including its caffeine, which can be used to encourage a second round of blooms on flowering plants. When using coffee in the garden, expect it to take one full growing season to assimilate into the soil.
Coffee is highly acidic and will affect the pH of the soil, causing it to become lower. This is an advantage with plants that feed heavily on the acidic nutrients in the soil; however, for plants such as vegetables or most trees, a neutral pH should be maintained. To ensure the soil remains neutral and still enjoy the advantages of composting with coffee, consider adding some oyster shells to the compost to balance out the compost's pH.
Plants such as citrus trees and roses need acidic soil to thrive. Over time, the soil begins to lose its acidity as the plants remove various nutrients from the soil. Adding coffee to the soil naturally decreases the pH back to an acidic level. Acidic soil also holds certain nutrients such as phosphorus more efficiently than alkaline soil.
According to the University of Washington, College of Forest Resources, coffee grounds also add numerous nutrients to the soil which all plants need for food. The primary nutrients that coffee contains are nitrogen, phosphorus and potassium. The secondary nutrients include calcium, magnesium and sulfur.