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Wood Ash in the Garden
Garden Tips Newsletter - January 9, 2002

With the onset of winter and colder temperatures many of us have started using our fireplaces. Many gardeners like to use the ash from their fireplaces or wood stoves in their garden. While this practice is quite common, gardeners should be aware that wood ash will raise the pH of the soil (for 15 lb/100 sq ft application the pH can change from 4.0-6.5). If the soil pH is already 7.0 or greater adding wood ash is not recommended. Wood ash does contain some nutrients; in general hardwoods contain five times the nutrients as softwoods. Wood ash contains 20-50 percent calcium carbonate (a type of lime), 3-7 percent potassium carbonate (potash), and 8-20 percent phosphorus pentoxide (phosphorus). Ashes also contain trace elements of sodium, magnesium, iron, copper, zinc, manganese, boron, silicon, and sulfur. Wood ash will also promote nitrogen loss from ammonia-based fertilizers such as ammonium sulfate or ammonium nitrate. If you plan to add high-nitrogen fertilizers to your lawn, or garden, stop applying wood ash approximately one month before application. Ash from burned trash, cardboard, and painted or stained wood can be toxic and should not be used in the garden.

These archived newsletters were written by Dr. Lelia Scott Kelly. Kelly is a Horticulture Specialist with the Mississippi State University Extension Service. Her office is in the North Mississippi Research & Extension Center, Verona.