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Ashy-Looking Compost


September 5, 2020

From Master Composter WR: Today my husband and I went to Soilutions and bought a cubic yard of compost. I noticed when shoveling it onto my new garden bed it is very black and looks almost ashy.  I had put some of my own compost there as well and side by side you could really see the difference.  Mine was a deep brown but not black or ashy looking. I don't make hot compost (except occasionally, accidentally, when I have more feedstock than usual).  Is it typical for hot compost to turn out like this that I got at Soilutions today?  Did it "burn"?  Does that affect its quality?  Sorry to be so ignorant about this.


Answer by RR: I have bought Soilutions’ premium mix several times, but truth be known, I prefer my own because their’s sheds water initially until it eventually gets saturated. Mine absorbs water right away. Probably has to do with the soil they mix their compost with. I don’t think it has anything to do with the hot process because the compost I’ve gotten from the Water Utility Authority’s SAF is very absorbent like mine.

Answer by JZ: My thoughts/ opinions.   Finished compost whether from hot or cold process looks the same in my experience. When sifted to remove undecomposed coarse material, then it looks to me like coffee grounds. If the sample is dry it will be pale, see actinomycetes. If moist it will appear darker. The picture you sent appears to be a dry sample.

a. The ashey appearance on some of the particles may be from bits of the fungus/bacteria actinomycetes.  

b. If you to add water to the sample, then I think the whole thing would become darker.  it’s a high carbon(black) substance.

It’s common when we rake leaves, yard trimmings from the soil that we’ll pick up soil particles also, which will end up in the compost setup.

Our local sandy soil particles are tan in color. Soil particles as they are inorganic do not decompose. So the tan color may be present in the finished product.  Soil particles in the compost when added to soil may then form relationships with the humus particles in the soil.

Great that you are soil amending.  I hope to do a winter wheat cover crop soon.    Keep up.     Best.    

Response by Questioner: Thanks.  You know I hadn't even thought to see how it appears wet.  Or to see whether it will shed water, as RR mentioned.  I'll do that (later when it's a little cooler.  :)  Sure appreciate your responses.

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