Wood Ash - An Overview

I used to consider wood ash to be waste but now it is a welcome component to my homestead.

I try my best to apply it to the ground in the winter season. This gives moisture time to mellow out the salts and buffer the soil before the growing season sets in. I'm especially pleased this year with the growth of my brassicas in the areas that have been treated with wood ash. As a general rule of thumb, 3 pounds of ash to 300 square feet annually maximum. This ratio has done well for me.

Historically, wood ash could be turned into potash to use as a fertilizer. This was accomplished by soaking the ash in water to settle out the solids and then boiling the lye rich liquid down into a white powder (potash). In other cases, 'raw' ash was applied for its soil benefits. Interestingly enough, some documents from the early 1900's indicated that some ash being sold as fertilizer was "heated and sweated" prior to sale in order to concentrate the ash into something that weighed less than raw ash. Another nugget of wisdom was to layer bones destined to be bonemeal with layers of ash. This is then moistened to soften the bones prior to be broken up and spread.

Advertisement found in 'Wood Ashes and Their Use' by T. Greiner circa 1895

What is the difference between wood ash and biochar?

Is it that wood ash is a byproduct of some other application?

Or that wood ash is powdery and biochar is chunk like charcoal?

When added to soil does it make a difference?

wow, thanks for creating this! I also have wonderings about how much of the remaining coals are considered biochar. I think I need to do more research.

Anne Miller wrote:What is the difference between wood ash and biochar?

Is it that wood ash is a byproduct of some other application?

Or that wood ash is powdery and biochar is chunk like charcoal?

When added to soil does it make a difference?

Ash is all the stuff in wood that won't burn. Biochar is elemental carbon from wood (or other biomass) that has been heated but not completely burned. The minerals that make up ash are in biochar, but the carbon in ash is in carbonate form.

Ash tends to be powdery because all the structures that held it in place are gone. In a really hot fire it sinters and forms slag and clinkers. These are the chunky bits that are hard to grind, and are a bit like volcanic glass. Biochar can be chunky or powdery depending on what it's made from and what you do with it after you make it.

Ash and biochar do very different things in soil. Ash is mostly a chemical modifier, adding alkalinity and minerals. Biochar adds structure, water and nutrient capacity, aeration, homes for bacteria and fungi, and its surface area has electrochemical properties that do all sorts of cool stuff.

Alexandra Malecki wrote:wow, thanks for creating this! I also have wonderings about how much of the remaining coals are considered biochar. I think I need to do more research.

All of them, unless there are bits that haven't carbonised all the way through. The first human use of biochar was probably unintentional, as the remnants of cooking fires were dumped and mixed into garden soils. The gardeners noticed the benefits and we can pretty safely assume that at some point they started doing it on purpose.

An outdoor survival class I took in the 70's suggested that for treating diarrhea, which is life threatening in a remote survival situation, that a handful of ash from your campfire, mixed with water and consumed was a remedy.
My friend from high school was a Pararescue Specialist in the AirForce. His survival training taught him the same.

Deters slugs, place around edge of garden.

Finns clean the glass of their woodstoves with ash. According to my Finnish mother.

My dogs sleep in dry ash in the Fall. More to do with the heat stored in the ground and being very dry. Likely. Does seem to help with black flies/mosquitoes in the early Summer a bit if they let me put it on their faces. Anectdotal only. Your experience may differ.

Use hardwood ash for making soap.  Concentrated enoug if an egg floats in the solution.

Thanks for the great info on so many other uses.

Stabilizing the nitrogen fertilizer  in urine by making it more alkaline. Also adds nutrients.

https://www.sciencedirect.com/science/article/pii/S0048969717302796

There's plenty more out there on this subject.

Phil Stevens wrote:Ash tends to be powdery because all the structures that held it in place are gone. In a really hot fire it sinters and forms slag and clinkers. These are the chunky bits that are hard to grind, and are a bit like volcanic glass.

I ocassionally pull stuff out of my RMH that are dense and chunky, but they have the consistency more of sandstone (or something friable) than glass. Is that simply ash?

What are some uses for slags and/or clinkers?

Ash also makes a good insulator / insulation.

I keep all the charcoal and ash when I clean out the stove. Both get used. Most of the charcoal becomes enriched biochar and ash sweetens our acidic clay.

Coydon Wallham wrote:
I ocassionally pull stuff out of my RMH that are dense and chunky, but they have the consistency more of sandstone (or something friable) than glass. Is that simply ash?

What are some uses for slags and/or clinkers?

That's slag or maybe sand if you put in branches that had dirt on them. The best thing to do with it is use it anywhere you need aggregate. I like to sieve it into various grades for adding to earth and lime plaster mixes. Or you can use it to bulk up garden beds and potting mix.

Tommy Bolin wrote:Finns clean the glass of their woodstoves with ash. According to my Finnish mother.

I think this is pretty common in Norway, the easiest way to do it is to dip newspaper (or paper towel) in water briefly, dip the damp paper in the ashes in the stove, and rub it on the glass. Most of the soot/tar carbon mix will come off immediately, but repeat if necessary with new damp ash paper. At the end wipe any residue off with just damp paper, no ash. I've seen this method recommended in other ash use discussions, but using a rag instead of paper. As far as I know everybody uses paper here - presumably rags would work just as well, but it seems more economical to use a couple of pages of newspaper. You can throw it in the compost afterwards, or leave it to dry out and burn it the next time you light the stove.