By: Sandy Feather ©2006
Penn State Extension
Q. I plan to use my wood burning stove a lot more this winter to save on heating costs. Can I use the ashes on my garden and in my compost piles?
A. You can use wood ashes sparingly in the garden, but I emphasize the word "sparingly." Wood ash reacts with soil much like limestone -- it raises the pH of the soil. However, since wood ash is very water-soluble, it raises the pH much faster than limestone, which can take six months to a year to do the job. That means you can get the pH of your soil out of whack quickly. High soil pH limits the availability of certain nutrients such as phosphorous, iron and magnesium. As a result, plants grown in that soil can suffer from deficiencies of those nutrients.
Cherry log split for firewood
Soil pH is measured on a scale that runs from zero to 14. A pH of 7.0 is neutral, with lower values becoming increasingly acidic. Higher values are increasingly alkaline. Most garden plants perform best when the pH is between 6.0 and 7.0. Acid-loving plants such as rhododendrons, dogwoods and blueberries appreciate a soil pH between 4.5 and 6.0, depending on the species.
The best approach is start with a soil test so that you know what the pH is before you begin applying wood ashes. If it is already high (more than 7.0), or if you plan to grow plants that prefer an acidic soil, avoid applying ashes at all. If it is moderately acidic (around 6.0), you can safely apply about 15 pounds of wood ashes per 1,000 square feet per year. You could also apply wood ashes to your lawn, since turfgrass grows best with a soil pH between 6.5 and 7.0. Again, be sure to start with a soil test and do not overapply the ashes.
Avoid adding wood ashes to your compost piles, because composting is an acidic process. If you add too much wood ash to your piles, it can raise the pH enough to halt the composting process.