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Winter Woodfires: Using wood ash

As you know, through winter we heat our home and cook using a woodstove, so we produce lots of wood ash as a result.  Our current woodstove has a very clever design where the ash tray can be pulled out and emptied easily, this makes cleaning much more pleasant than when you have to scoop out all the ash.  We have to clean out the ash tray every couple of days if we have the woodstove burning every day.

eight acres: how to use wood ash in the garden
 A bucket of wood ash
We don't see the ash as a waste product though.  Wood ash is all the mineral matter remaining from the wood that was burnt, so its great for adding minerals to garden soil.  It usually also contains some unburnt carbon (biochar).  I spread the ash through the garden and tip it into the compost as well.  Wood ash is good for chickens to dust bath with, so I put it in their nesting boxes with a layer of wood shavings.
Spreading wood ash on the garden - I just hose it into the soil
I thought it would be simple to find out the mineral composition of ash, but it took me a while to figure out why the elemental composition didn't add to 100%.  Then I realised the balance is oxygen, as all the elements are present as mineral oxides.  Anyway, the composition depends on species of wood, the part of the tree, the growing conditions AND the temperature of the fire, but roughly, its 30-60% calcium oxide, 20% potassium oxide, 10% magnesium oxide, 10% sulphur oxide, and small amounts of iron and sodium oxides, as well as trace minerals.  So wood ash is a good source of calcium and potassium, and some other minor minerals.  Both calcium and potassium and very important for healthy plants, so wood ash is a great way to return these minerals to the soil.

The clever ash tray on our wood stove
Two things to consider before you start spreading wood ash around:

1) make sure it is completely cold.  I spread ash directly from the woodstove onto dry mulch once and had to very quickly stamp out a fire, even though it didn't seem hot at the time, it was still very hot inside.  Its also best to use a metal bucket to store ashes, plenty of fires start from plastic buckets of ash melting through, and keep the bucket on concrete or dirt rather than wood or plastic.

2) test your soil pH as all those mineral oxides form hydroxides with water, which will increase soil pH.  Soil pH tends to decrease as calcium ions are leached, so usually it is safe to add wood ash to maintain calcium ions and a neutral pH (7), but if you have naturally high pH soil, then don't add wood ash.

Speaking of hydroxides, the other use for wood ash is to soak it in water to make lye for soap making.  This is the traditional method, and much more difficult that using purified sodium hydroxide (caustic soda) like we can do today.  I'm tempted to give it a go one day though.

How do you use your wood ash?


  1. I dig mine into the onion beds and add it to my home made liquid feeds (comfrey and nettle tea) for tomatoes and peppers to feed on as well as adding it to their mix that I plant them into. I never thought of letting the chickens have a dust bath in it.
    Thanks for the chemical composition of wood ash. I always wondered what I was putting on the soil.

    1. the potassium is great for your tomatoes, helps them to flower :)

  2. Hi Liz, I have been using mine in a similar way- apparently it is really good for citrus.It was interesting to hear about the chemical composition.I over did it in one of my beds though and threw the PH out , so that was really good advice about checking soil Ph .
    Always interesting reading over at your blogx

    1. the potassium is also great for the citrus!

  3. I spread it thinly over the garden once a year and the remainder goes on pasture. No problems with doing it this way for years now. but like you say, the fire needs to be out of it and you don't even want to set a metal bucket of it on anything that might burn. I find that if I can spread it on or after a rain it does well. Have a nice winter, we are getting into the heat of summer and I am actually installing steel flu liners for 2 more wood stoves and need to do maintenance on the main wood furnace.

  4. I give it to the chooks, in their dome, they are very happy to spread it around. It gives a nice boost to the soil, in combination with their manure, kitchen scraps and all the stock bones that they’ve buried then covered with some mulch. Makes a great start for planting the next lot of veggies and the fruit trees that border them.

    1. I need to get my chickens into the garden to do some work!

  5. Last 10 years we have central heating in our house. My dad is sick and we can't chop and store wood anymore. But when we had wood ash we used it to melt icy paths during the winter. Ash melts ice just like salt only it doesn't work so aggressive and animal paws don't get damaged.

    1. that's a great idea (not that we get ice or snow here, but useful for others!)

  6. Great post - top info. I use wood ash whenever I can. It is a great replacement for lime being alkaline. The garden loves it, the slugs and snails aren't so fussed. :)

    1. good point, got to love anything that keeps the slugs away!

  7. your post prompted me to look into wood ash and how it is used for soap making, sounds very time consuming but much better than using caustic soda definitely something to research further

  8. Great post, this will be a featured post, on the HomeAcre Hop on Thursday.
    Thanks for sharing!

  9. My ash goes into all the holes that the pesky four-legged children dig. After reading this may have to pop into the dust holes the chooks have dug.


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