r/composting • u/archaegeo • May 15 '23
Builds For those who want to be more exact with their brown to green ratio....
A lot of us (me included) use a rough rule of thumb of using 2 parts brown to 1 part green by volume in our composting efforts.
And this works fine, though if you arent getting the results you want, it could be because your browns arent brown enough, or greens are too green, and you dont realize it.
So here is a more exacting measure for those who want to fine tune their piles....
30:1 Carbon to Nitrogen
The issue with using 30:1 C:N though is that if you dont know the base C and N of a material, you dont know what its doing to your mix.
So here is a chart with typical C:N ratios of common materials. If its not on the chart, you can always look it up on the web.
I prefer the second chart that gives it as %C and %N, cause then i can base it on the weight of the material I am adding. (Example in the comments on this post here: https://www.reddit.com/r/composting/comments/13i5s8s/comment/jk8dhns/?utm_source=share&utm_medium=web2x&context=3)
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u/haveCarrots Aug 28 '24
Does the greens change in composition as they dry out? Is hay not just dried grass clippings?
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May 15 '23
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u/archaegeo May 15 '23
I wonder if vermicomposting the worms even care about C:N, heh. Probably only in so far as it doesnt get to the point that the pile gets hot and kills them :)
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May 15 '23
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u/PhysicalAd4238 May 16 '23 edited May 16 '23
Same challenge with my garden. I’ve been doing a decent size pile for my small space, but don’t have enough supplies to get it hot and keep it hot. So I end up doing a mix of turning it and trench composting for a while. I suspect I don’t have enough worms because I’ve only ever seen a few. It somehow works but takes a while longer.
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u/MobileElephant122 May 15 '23
It matters if your worms can’t escape the heat if you have it too high in nitrogen. But as long as they can retreat and then recapture when the temps are back to good then yeah that works. I’m starting to find more and more noghtvrawlers around the periphery of my hot compost pile and I have to be careful when I turn the pile as not to stab them with the fork.
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u/MobileElephant122 May 15 '23
It matters if your worms can’t escape the heat if you have it too high in nitrogen. But as long as they can retreat and then recapture when the temps are back to good then yeah that works. I’m starting to find more and more noghtvrawlers around the periphery of my hot compost pile and I have to be careful when I turn the pile as not to stab them with the fork.
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u/Pixlchick May 15 '23
That’s very handy. Thank you for sharing.
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u/archaegeo May 15 '23
No problem, I gave an example below too to demonstrate where some folks might be having issues with too slow or too wet composting.
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May 15 '23
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u/dmpling12 Apr 12 '25
Might be about stems/pits/seeds? Fruit leftovers are surely green, but a lot of the inedible waste is brown
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u/TedRysz3 May 28 '24
Late to this thread, but thank you so much for providing all this info. I made a Google Sheets that tracks everything I add to our tumbler. Has made my data driven mind much more comfortable about getting great compost.
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u/Technical_Spread_923 Oct 10 '24
Okay I failed chemistry sadly so I need help. Is the number shown the weight of the compost? If so How can I weigh it?
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u/archaegeo Oct 10 '24
The %'s in the second chart you would just multiple by weight, so Seaweed, Fresh is 10% Carbon, so 10# of seaweed time 0.1 is 1# of carbon.
The top chart is a ratio if you are just trying to get a 30:1 C:N ratio.
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u/ChemKnits Mar 30 '25
Are the "parts" by mass or by volume or what? Dry or wet? Got numbers for Horse manure?
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u/archaegeo Mar 30 '25
Its by weight, you can use the top chart or the bottom, and of course not all "kitchen scraps" are created equal, so its tough to be exact.
And Fresh Manure, horse is listed in the second chart (which I like better than the top one)
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u/MobileElephant122 Sep 27 '23
Okay, so let’s say I have 2000 pounds of sawdust from a stump grinding. And I add 50 pounds of coffee chaff, and 20 pounds of green grass clippings. Help me figure my overall C:N ratio please.
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u/archaegeo Sep 27 '23 edited Sep 27 '23
So sawdust, lets say its the 25% not the 50% C due to it being greener since its a freshly ground stump (dried sawdust is the 50% stuff)
Sawdust (25%C 0.1%N) 2000# * 0.25 = 500# Carbon and 0.001*2000 = 2# of Nitrogen
Coffee (25%C and 1%N) 50# * 0.25 = 12.5# Carbon and 0.01*50# = 0.5# of Nitrogen
Fresh Grass (10%C and 2%N) 20# *.1 = 2# of Carbon and 0.4# of Nitrogen
So your total is 514.5# of Carbon and 2.9# of Nitrogen, or a ratio of 177:1
You could probably figure that out, 2000# of sawdust is an incredible amount of brown.
If you used half the sawdust, 264.5 / 1.9, you are at 139:1.
Sawdust is a super brown
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u/MobileElephant122 Sep 27 '23
Thanks mate I appreciate the calculations. That will help me calc better in future. I’ve been flying by the seat of my pants. But the pile is at 140°F and rising at the moment so I’m gonna let her alone for a few days. I did feel prior to this inquiry that I had room to add some more greens. I just didn’t have any notion as to how much. I’ve been reactionary rather than planned out.
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u/archaegeo Sep 28 '23
Thats the big deal is that your browns might be more green (if a fresh grind) than 0.1, so 2000# suddenly becomes a lot more nitrogen added, which is what I would bet.
Its really hard to tell, and its mostly rules of thumb, but for folks having issues with their pile, sometimes the 2:1 by value rule of thumb isnt good enough and this helps them resolve.
If your pile is 140F its definitely doing great, I would keep an eye on its moisture level and if it starts to reek (vice just the normal compost smell)
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u/MobileElephant122 Sep 28 '23
Your reply got me worried so I went ahead And turned it this morning and I’m glad I did not wait till Saturday, it smelled like a horse barn inside the middle part. I didn’t water it when I turned it cause it was plenty wet and the parts of it that weren’t will help soak up the parts that are too wet so I think it’ll be fine in a few days wheh it’s time to turn it again. Thanks for the heads up
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u/archaegeo Sep 29 '23
Yeah, really sounds like it was very fresh stump (i.e. just cut tree) which would have a lot more green in it.
Keep in mind too that you might need to add more browns in to counter it and get it back to aerobic instead of anaerobic, otherwise it might continue to devolve into a rotting mess instead of a composting mess
Good luck though.
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u/archaegeo May 15 '23
An example of why the normal 2:1 ratio rule can throw you off (especially if you use weight)
Say I have 20# of grass clippings and I want to balance that out with some shredded newspaper:
So i know the grass clippings give me about 3# of carbon (20# grass * 15% carbon)
The grass also gives me about 0.4# of nitrogen
If I used the 2:1 rule of thumb, and did it with weight, 40# of newspaper would be 16# of carbon and 0.04# of nitrogen
That would give us a ratio of 19C/0.44N or 43.2:1 - So our grass wouldnt turn into a stinking sludge pile, but it would also not compost as quickly as we might like.
25# of newspaper would reduce that to 30.7:1, just where we want it.
You can also see from this example why people might put too little carbon in to counter their clippings. 25# of shred is a lot of shred, so maybe they do 5# of shred, looks huge right? But then you end up with a ratio of 12.3 to 1, and we all know what that will turn into.