Many people start the day with a fresh cup of coffee and then discard the used grounds. A better use for those old grounds is in the garden. Old coffee grounds contain many nutrients plants need. The grounds are biodegradable and available.
Coffee grounds are a source of phosphorous, potassium, calcium and magnesium, but they are particularly rich in nitrogen. Nitrogen encourages the growth of new stems and leaves. Without it, plants become yellow and stunted. Nitrogen is water-soluble and leaches out with rain. Coffee grounds, when moistened, release nitrogen into the surrounding soil, effectively replacing that lost by leaching. Coffee grounds from a drip coffee maker make better fertilizer than those boiled by a percolator, as they have higher nitrogen content.
Soil pH has a significant effect on plant growth. While most plants thrive when set in soils that have a neutral pH of 6.8 to 7.5, fruit trees, such as apples, cherries, peaches, nectarines, pears and plums, flourish in slightly acidic soils with a pH of 5.5 to 6.7. Incorporating coffee grounds into the soil surrounding the base of the tree lowers the pH to a more suitable range for fruit production.
Coffee grounds spread around a tree's base decompose gradually, releasing their compounds in the process. Drawn to the strong coffee aroma, earthworms and other soil-dwelling creatures pull the old grounds beneath the surface of the soil, improving soil structure by increasing aeration and drainage. While the odor of decomposing coffee grounds may be attractive to some, it repels others. Spent grounds keeps root maggots at bay and stops local cats from using the garden as a latrine.
Spread a 1/2-inch layer of old grounds around the base of the tree in early spring or sprinkle them around the tree throughout the growing season. Keep the grounds about 6 inches away from the tree's trunk. Direct contact with damp coffee grounds weakens the bark, leaving the tree vulnerable to invasion by pests. Incorporate the grounds into the soil with a sturdy garden rake or leave them as they are and let earthworms do the work.