Coffee grounds can be spread in a thin layer less than one inch deep and worked into the top few inches of soil to add organic matter. If you are planting acid loving blueberries or azaleas place used coffee grounds in the planting hole - it will add acidity. The grounds will not make the soil more acid when it is worked into the top layer of soil because it will compost and become neutral in pH. A thick layer of coffee grounds can form a water blocking layer so be sure it is mixed into the soil. Keep growing, Marianne Binetti