With the onset of cold weather and the burning of fireplaces, many gardeners are asking if the wood ashes are good to use as garden or flowerbed fertilizer. In a nut shell not really.
You may have read about the value of wood ashes in various garden magazines or heard about using them from old gardening friends. In some parts of the country they are good to use. But, they may not be the best fertilizer to use around here.
So, as Paul Harvey would say: "... and now the rest of the story."
Wood ashes contain no nitrogen (N) because it is lost during the burning process. Likewise, they contain little to no phosphate (P). The only valuable nutrient in wood ashes is potassium (K). Unfortunately, in most local soils, the levels of K are quite high and little extra is needed. In fact, it is stable in the soil and does not leach out.
The only way potassium is lost is by plants using it for growth and development. This is why a soil test is recommended before adding nutrients. It is difficult to know what is needed when you do not already know what is available.
Another problem is that wood ashes function like lime to increase the pH of soil. Here again, in our area, soils are calcareous, or derived from the native limestone. The pH is mostly neutral so the use of lime is not necessary. The increased lime may raise your soil pH to an undesirable level. So, the benefits of wood ashes in most garden soils is not all that great.
To use wood ashes to their greatest potential, mix them with the compost pile to give a more balanced fertilizer product. Likewise, compost is usually slightly acidic so ashes would raise the pH to a more desirable level. In either case, wood ashes are better mixed with some other source of organic material rather than being applied by themselves.
It would seem that wood ashes from the fireplace are a good source of nutrients and minerals. Unfortunately, they are not. However, if you do decide to add wood ashes to your garden or flowerbed, spread them in a very thin layer and never in a concentrated amount. Better yet, incorporate them in with the compost pile. Although you may see little initial benefit from this practice, you will be creating a more complete compost in the long run.
Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more gardening information, call the Master Gardener Hotline, 843-7058, between 9 a.m. to noon and 1 p.m. to 4 p.m. Monday, Wednesday or Friday.