Wood Ashes: A valuable source of potash. Wood ashes generally contain from 1 to 10 percent potash and 1-1/2 percent phosphorus. They can be mixed with other fertilizing materials or side-dressed around growing plants in acid soils. Apply about 5 to 10 pounds per 100 square feet. They can be used in any soil if mixed with organic matter and composted first. Avoid using wood ashes around blueberries or other acid-loving plants and don’t use heavily even in alkaline soils. Only wood ashes, and not coal ashes, should be used in the soil or compost. Wood ashes are also an effective tool in controlling slugs.