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Fireplace Ashes


March 1, 2023

Can or should I mix my fireplace ashes into my shredded leaf compost pile.  I was told it would break the leaves down faster and was good for my soil.


Answer by WR: Unfortunately, most advice online, etc., is from people who don't live in a desert like we do here in New Mexico.  Fireplace ashes are quite alkaline. Here in New Mexico, our soil is very alkaline. I'd be hesitant to add them to compost here because we need less alkalinity, not more.  However, if you live somewhere where the soil is acidic, I think it would be fine to add a small quantity to your compost.  (Soil tends to be alkaline in dry climates where there is not a lot of rain to wash the high PH salts out of the soil.  Soil tends to be acidic in moist climates, places that are a lot greener than we are here in New Mexico.)

I am going to copy this to our compost-questions email list and you may hear other thoughts about this.  I'd also be interested in what others think about this.  I do know that finished compost usually has a good balanced PH so I may be wrong to completely avoid putting ashes into compost. Perhaps the composting process itself can bring balance here, especially if you don't put in huge quantities of ashes.  I hope others will know more about this than I do.

Answer by RR: Thanks for your interest in composting. As WR said, there is very little information on the internet dealing with composting in the high desert, which is very different from composting in more humid climes. Wynette's response is spot-on regarding composting ashes. I just cleaned out my fireplace, and as much as I dislike sending things to the landfill, I bagged up the ashes and put it in the trash barrel. As WR also said, putting small quantities of ashes in your compost would probably be alright since the biological composting process tends to neutralize the pH over time, but whatever you read, ashes are not a beneficial addition to your composting operation in New Mexico.

Answer by JZ: I agree with both colleagues WR and RR. If you want shredded, moist brown leaves, which would be primarily carbon, to decompose in a timely fashion then an appropriate addition would be greens/nitrogen - for example: fruit and veg scraps, green weeds without

seeds, hair, feathers, fur, coffee grounds (many shops will save them for you), brewery leftovers, herbicide free vegetarian animal manures and urine. A simple useful guide is to add 1 measure of greens (nitrogen) for every 2 measures of browns(carbon). Purchasable nitrogen containing products:  alfalfa pellets, feather meal, cotton seed meal, blood meal and fish emulsion fertilizer are available at farm supply stores.

In addition to adding greens, you might also inoculate the leaf pile with small amounts of finished compost to increase the microbial activity - about a cup of compost sprinkled on every 5 “ of leaf litter.

A very dynamic (fast) way to decompose leaves would be hot process composting which is described in this recently revised brochure, Composting in the Desert

Let us know if you need more info.  Compost on!  

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