Used coffee grounds  Used coffee grounds are the waste product from brewing coffee, in the final stages of coffee preparation. In the late 19th century, used coffee grounds were used to adulterate pure coffee. In gardens, coffee grounds may be used for composting or as a mulch as they are known to slowly release nitrogen into the soil. The dry coffee grounds contain significant amounts of potassium (11.7 g/kg), magnesium (1.9 g/kg), and phosphorus (1.8 g/kg). They are especially appreciated by worms and acid-loving plants such as blueberries, although due to acids being leached from the grounds while in use, they typically have a neutral pH. Used coffee grounds are particularly noted as a soil amendment. Gardeners have reported the use of used coffee grounds as a slug and snail repellent, but this has not yet been scientifically tested. Some commercial coffee shops run initiatives to prevent the grounds from going to waste, including Starbucks' "Grounds for your Garden" project, and community sponsored initiatives exist, such as "Ground to Ground"  or the 'Green Coffee Shop Scheme' in Cambridgeshire, UK. In divination and fortune-telling the patterns of coffee grounds are used for predictions. Initiatives have succeeded using coffee grounds as a substrate for the cultivation of mushrooms (including oyster mushrooms). Used coffee grounds have other homemade uses in wood staining, air fresheners, and body soap scrubs. They may also be used industrially in biogas production or to treat wastewater.