Thursday, February 24, 2011

Ashes From Your Fireplace- Compostable or Not?

Who doesn’t love gathering around a nice crackling fire in the winter, wrapped in a fuzzy blanket with a mug of hot cocoa in one hand and a toasting marshmallow in the other? Heck, I don’t even like marshmallows and it sounds like fun to me. But after the fire has died and the Norman Rockwellian merriment subsided, what do you do with the pile of ashes left in the fireplace? Is it okay to toss them in the compost bin?

Maybe, But Only in Small Amounts.

Be careful, and not just because leftover embers could burn you or start a fire in your compost pile (I know, you know fire = hot, no need to roll your eyes).

Wood ash is very alkaline so adding too much can raise the pH of your compost bin, which can wreak havoc on your little microorganism buddies breaking down materials in your bin. A neutral pH is the best environment for microorganisms.

So just a sprinkle is fine, but you don't want to dump a whole bucket in there.

That said, adding a light layer of wood ash can be a good source of lime, potassium, and trace elements. And sometimes you may want to neutralize an acidic bin. For example, if you frequently make fresh squeezed lemonade or orange juice (yes, I feel your eyes rolling again) and contribute lots of acidic peels to your bin, the wood ash can help neutralize the pH of the bin.

Curious Minds Want to Know

The reason wood ash is alkaline is that when it comes in contact with water it creates caustic lye. This is how you would make soap if you lived say, in a little house on the prairie.

Another reason you should use wood ash in moderation is that Cincinnati sits on a giant bedrock of limestone (also a higher pH) and shale. So we usually do not have acidic soils that you would need to neutralize. As always, we recommend testing your soils before using too much wood ash on your garden or in your bin.

Wow, two science lessons in one post- hold onto your hats.

Did I Mention the Answer is Maybe, with Caution?

One last tip- never use ashes from a barbeque pit or charcoal grill. These ashes can contain chemicals which could be harmful to the soil.

So you can compost wood ash if you 1) wait until it’s completely cooled, 2) use in moderation, and 3) don’t use BBQ ash.

If you burn a lot of fires in the winter, you should find another method of using your wood ash. Has anyone ever found a good use for this stuff? If so, leave a comment!


  1. I do add some to my compost heaps. never quite sure if it is good or not. I will try localized around citrus rinds.

    Other possible use scatter on shoveled snow areas. Such yields a darkened color which speeds heat/melt/evaporation. Of course plain old sand does the same.

  2. Ashes are good for sprinkling on your plants to get rid of some pest, they eat them along with the leaves and the sharp edges of the ashes cuts them up inside and kills them. I use it on my potato plants and it works pretty good, of course you have to reapply after a good rain.

  3. I've also heard of throwing them on snow/mixing with salt for our annual snow dusting here in cinci. But, this also makes for a nasty mess when the stuff melts...

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  5. I use wood ash VERY sparsely in my compost 2 or 3 times a yr. What you can do with the rest is sprinkle VERY sparingly in a wooded area VERY VERY sparingly. Then I use concentrated amounts right up against the fence lines; this keeps grass and weeds at a minimum in areas that are difficult to reach with the mower. This method is not recommended around tree bases or gardens; you will injure or kill your plants. Good for killing honey suckle stumps that won't go away!

  6. I agree, ashes from the fireplace do really have enough nutrients to be composted. Minerals like carbon and nitrogen are essential for a good compost that ashes can provide.

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  8. I have been composting for many years and started burning wood a couple of years back and have added most of my wood ash to my compost pile. Now I am concerned that it may really need to be amended with what nitrogen or what?

    It doesn't seem that adding more carbon would be the solution.

    My first stab is to add grass clippings probably 10 bags or so. It is a pretty good size pile about 12 X 5.

  9. It sounds like you have a very large pile so the wood ash may not affect the pH too much. If you are concerned, I would recommend adding something that is acidic to balance out the basic ash, something like orange or lemon peels. Also turn the pile so the ash is incorporated into the pile and not concentrated in one area. As long as your pile is still decreasing in size and heating up, you should be fine.

    Compost piles are usually very forgiving, so don't stress out about it too much.

  10. Can I put my cooled ashes in the city provided compost bin?

    1. Some communities may allow this but most will not. I would recommend contacting the city in which you live to learn their policy.

  11. The "no BBQ ashes" rule only applies if you are using commercial briquets (which contain binders and such) and lighter fluid. If you are using wood or natural lump charcoal and starting your fire with newspaper and kindling, this is not an issue.

  12. Wood ashes work very well when dusted into your humanure bucket or outhouse hole. This keeps the odor to a minimum and balances the pH.