Spreading a thin layer of ash onto your lawn helps it grow, according to Oregon State University. Using wood ash as a lawn fertiliser provides potassium and lime, nutrients that all lawns need. Hard woods such as oak are recommended as they produce the most ash per pound of wood and also contain the highest percentage of nutrients.
Too Much Ash Is Harmful
According to University of California at Davis, applying too much wood ash can increase your lawn's alkalinity and salinity and harm grass. UC Davis recommends applying ashes sparingly when grass is dry and watering the lawn immediately after application.
Oregon State recommends using wood ash in conjunction with a fertiliser that contains nitrogen as wood ash only contains potassium. Avoid using ashes from coal or chemically treated wood on your lawn as these types of ash are not safe for plants.