Using Wood Ashes in the Garden

After the long winter many Connecticut residents are faced with a small problem. What does one do with the wood ashes left from their wood burning stove or fireplace? An average cord of wood, depending on the efficiency of combustion and wood type, will yield approximately twenty pounds of ashes or the equivalent of one five-gallon pail. Over the winter, this can add up to quite an accumulation of wood ashes.
Wood ash acts on the soil much like limestone in that it raises the pH or alkalinity of the soil. Consequently, many wood stove burners dump the ashes on their garden site with the thought that they are improving the soil condition of their garden. Yet unlike limestone, which can take six months or more to take effect, wood ash has high water solubility and quickly changes the soil pH. This can cause a problem with raising the soil pH over the optimum level of 6.5 to 7.0 if we spread too many ashes in the same area. A soil pH over the optimum level can affect plants as adversely as a pH that is too low. High pH will limit the uptake of important soil nutrients needed by the plant such as phosphorous, iron, and magnesium.
A safe rate of wood ash application for a garden or lawn area would be twenty pounds per thousand square feet or a five-gallon pail full of wood ash. Twenty pounds of wood ash is equivalent to six pounds of ground limestone per thousand square feet. If the soil is in the proper pH range, this rate of application is considered appropriate for yearly treatments. After wood ash application, we should need no additional lime, with nitrogen and possibly phosphorous being the other plant nutrient requirements. The wood application will also supply potassium. We should mix the application of wood ash to the garden soil well. Certain common garden plants will benefit from a small amount of wood ash being applied around them every year or two. These include, but are not limited to lilacs, peonies, boxwood, Japanese maples, lavender, Russian sage, caryopteris, and many others. Lawns and vegetable gardens will especially benefit from ash applications.
Having a soil test taken once every two years from your garden and lawn is wise. The recommendations for soil treatment, including any adjustment of soil pH, will give one a more accurate means to care for their garden and lawn.
We should make careful consideration when applying wood ash to lawn and garden sites. A measured application can be beneficial to increase soil pH. However, excessive applications of wood ash will increase the likelihood of soil related problems.