Is Wood Ash Safe to use in a Vegetable Garden?

By Roger Miguel | Monday Monday Staff -    2017-11-23

I have been asked a number of times about the use of wood ash as a soil amendment in vegetable gardens. This interested me as often I will add the ash from my small fire pit into my compost as it is something that I have seen family do in the past.
Today I thought I would look into the practice to see if using wood ash has benefit in the garden while diverting it from the landfill.
Today’s general hypothesis is that Wood ash has benefit when used in a vegetable garden.
In order to understand this issue a little more, we will need to ask some much more specific questions
Is wood ash a fertilizer?
Will wood ash change the pH of my soil
Is wood ash a fertilizer?
The University of Wisconsin Extensions produced an information bulletin on the use of wood ash as an agricultural amendment and substitute for lime. In their research the sampled 16 ash samples from local sources and found 12 of the 15 commonly tested for elements that are essential or beneficial for plant growth.
Notably, there were significant concentrations of Calcium, Magnesium, Phosphorus, and Potassium all nutrients required by plants in higher concentrations.
They also noted some other elements that could become toxic however their concentrations are low enough to represent what you would expect to find in most soils naturally.
It would seem that wood ash does have value as a fertilizer, however, most notably it is missing nitrogen which is lost during the burning process.
Regardless there are many studies evaluating the use of wood ash and correlating over many years to the increased production of commercial crops. This proves to be most effective in acidic soils when the researchers were growing forage crops for livestock that grow best in neutral or slightly alkaline soils.
This leads us to the next question will wood ash change the pH of garden soils?
Wood ash is very effective at increasing the pH of soils.
Many sources cite the use of wood ash as a replacement for lime in agricultural practices. The purpose of which is to raise the pH often from acidic conditions to a near neutral pH of 7.
This is done to bring the soil pH into the optimal range for the crop. Having the pH of the soil close to optimal allows the crop to access the available nutrients resulting in higher yields.

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