Composting 101- Carbon to Nitrogen Ratio

Like most things in life, you have to do a little research to make it happen correctly. I really had no idea when thinking of starting a compost that there would be science involved. And we know how much I love science from the “World of Plastics” blog over the summer. So, now I know, I can’t just throw whatever I feel like into my compost, I have to be careful and measure my Carbon to Nitrogen Ratio. ‘C:N’ ratio is how the scientists do it. Let’s see if I can figure it out.

“The C:N is a ratio of the mass of carbon to the mass of nitrogen in a substance. It can, amongst other things, be used in analyzing sediments and compost. Carbon-to-nitrogen ratios are an indicator for nitrogen limitation of plants and other organisms. C:N ratios in the range 6-8:1 are usually from marine sources, whereas higher ratios are likely to come from a terrestrial source. When composting, microbial activity utilizes a C:N ratio of 30-35:1 and a higher ratio will result in slower composting rates. However, this assumes that carbon is completely consumed, which is often not the case. Thus, for practical agricultural purposes, a compost should have a initial C:N ratio of 20-30:1An example of a device that can be used to measure this ratio is the CHN analyzer. However, for more practical applications, desired C:N ratios can be achieved by blending common used substrates of known C:N content, which are readily available and easy to use.” This is how Wikipedia explains it. Confusing right? I think we just need to concentrate on that last part, ‘blending common used substrates’. Let’s find out what they are.

When talking about organic materials, they say things like ‘too green’ and ‘too brown’, these are all terms to help measure your ratio. This site gives you a better breakdown of some organic materials you may be using in you compost. Materials containing high amounts of carbon are considered “browns,” and materials containing high amounts of nitrogen are considered “greens.” Here’s another site and chart to help you out with that too. Since I’m living in an apartment complex materials like yard trimmings and wood waste will be unavailable to me. I have to find other ways to keep my ratio.

The ‘too green’ problem is something I may run into, too much nitrogen. Since my compost will mainly be fruit and vegetable peelings and other food waste the chances of it becoming a sludgy, smelly mess are on the high side. To avoid this we must include the browns.

‘Too brown’ can cause it’s own problems. With Fall on our heels we may be tempted to throw all those leaves and branches in our composts. With this you will have too much carbon and you may end up with woodlice and ants.

We really have to make sure that this mixture is just right. I’m not interested in a smelly mess and who wants any reason for more ants to hang around. Just Right will be if “the green items will contain bacteria that will generate the initial heat that is required by the process. A healthy compost bin is a living ecosystem. By keeping a good mix of green and brown material you will provide the perfect conditions for a variety of mini-beasts and can let them do all the hard work.” according to This site has tons of useful information should you run into a problem.

Next time we will talk about some of the ‘just right’ items we will be putting in our compost. If all goes well, we will have a continuous supply of nutritious compost for our gardens.


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