County Ag News
The use of ashes is commonly viewed as a practice which will improve your garden since it is a source of potassium. This is pretty much correct, however, the major component in wood ash is calcium carbonate which is a liming agent with about 1/2 to 1/3 of the acid neutralizing capability of conventional aglime.
Wood ash contains between 25 and 50 percent calcium carbonate as its major component. Approximately 10 percent is potash, and less than 1 percent phosphate; there are also trace elements of iron, manganese, zinc, copper and some heavy metals. However, these numbers vary, depending on the wood being burned and depending on the combustion temperature.
For the home gardener wood ash can be a valuable source of lime, potassium and trace elements.
However there are cases where a homeowner has applied ashes to the same garden area for a period of years and as a result the pH has increased to 7.5 or higher. For most garden vegetables a pH between 6.5 and 6.8 is considered optimal. Before adding ashes it is recommended that you have your soil analyzed to see if there is a need for lime or potassium.
Where soils are acid and low in potassium, wood ash is beneficial for most garden plants except acid-loving plants such as blueberries, rhododendrons and azaleas. Wood ash may be used on flower beds, lawns and shrubs. Lawns needing some lime and potassium can also benefit from wood ash. Apply no more than 10-15 pounds of ash per 1,000-square feet of lawn; at high levels, ash can be toxic.