Fireplace ashes

Asked March 9, 2020, 3:55 PM EDT

Hi, I use only seasoned wood from a local provider in my wood burning stove. can the ashes be used as a fertilizer? if so, how much and how often. What type of areas, for example vegetable plot, fruit trees, lawn? Thanks.

Clackamas County Oregon

1 Response

Yes, wood ash can be applied to the soil as a source of highly soluble potassium and phosphorus, but with caveats:

  • Screen or pick out the obvious chunks of wood
  • Ash increases soil pH
  • That's not a bad thing, as our soils on the west side tend toward acetic, and the rainfall supports that tendency.

Whenever you implement a soil fertility program that changes soil pH, it behooves you to implement a routine pH testing strategy. It doesn't have to be a laboratory analysis - tho' one of those every 5-8 years is a good idea.

However, you should begin some type of pH test kit monitoring, and if/when soil pH rises about ~7.5. STOP adding ash to that particular area. Monitor annually, at about the same time of year every year, and record the results so you can see any developing trends.

Ash contains chemical salts and highly soluble potassium and phosphorus. Soluble forms of potassium are fairly available, but soluble forms of phosphorus are rare, making ash a valuable soil amendment.Beware of excess chemical salts, however, as these can burn plant roots.

Remember that the dose makes the poison: the Extension recommendation for wood ash is not more than 5-10 pounds of ash per 100 sq. ft. per year. I’ve conferred with the public about composting for 30 years; the only person I ever saw doing everything wrong had overapplied ash.

This extension publication is no longer in the catalog, but the information is still good. Download Using Wood Ashes in the Home Garden at no cost from the ScholarsArchive@OSU.

All of the uses you propose are fine.