For those with wood fires in their home, disposal of wood ash is a concern. Wood ash was used in the past to make lye for soap, used for traction in winter weather, used for scouring dishes and used in scalding barrels to remove the hair from hogs says the University of New Hampshire. It is now used in the garden.
According to Clemson University, from the 1700s to the early 1900s, wood ash was used for the chemical extraction of potash and alkali for fertilizers. Wood ash is no longer considered economically viable for the commercial production of potash however, and its use is dropped. Land application is down, and over 90 percent of wood ash is dumped in landfills.
Wood ash is composed of inorganic and organic residue from wood combustion. The quality of wood ash depends on the quality of the wood being used. Hardwoods produce more ash than softwoods do. Generally, six to 10 percent of the wood becomes ash while the rest is reduced to smaller parts and taken away due to heat and air.
Wood ash carries with it the 13 essential elements for plant growth. Nitrogen and sulfur are lost in the gases for the most part says Oregon State University, but trace elements remain. Carbonites and oxides become valuable liming agents, which are best utilized in the soil.
Ash is used in soils that are acidic and low in potassium. Wood ash, according to the University of New Hampshire, raises soil pH. The ash is also water soluble and improves the water retention of sandy soils. Wood ash changes soil pH rapidly, so if too much is added, it will make the soil alkaline. This will reduce a plant's ability to absorb nutrients from the soil.
Wood ash is safely applied to soil at a rate of 20 pounds per 1,000 square feet. Twenty pounds is the equivalent of one five gallon bucket of wood ash. Wood ash is never applied to soil that is growing acid loving fruits and vegetables such as blueberries. Wood ash is tilled into the soil to mix it thoroughly before planting.