Practical steps to get the Carbon to Nitrogen Ratio right

Composting is a scientific art. To freely practice art, we need to learn precise techniques. Getting the precise carbon to nitrogen ratio (C/N ratio) is crucial in composting because it decides if your pile will ever finish or not.

Carbon burns to gives human body energy, while nitrogen build body cells. Same rule for bacteria. Bacteria use carbon to gain energy and nitrogen to build their bodies. So, if you have carbon but don't have enough nitrogen in your composting pile, the population of bacteria will be limited so your pile will never finish. However, if you have too much nitrogen but not enough carbon in the pile, bacteria won't have the energy to work though the nitrogen so the pile will have excessive nitrogen and it will smell like rotten egg.

Getting the right CN ratio in the beginning will make composting easier until the end. For mixing the composting ingredients, you may hear that the ideal Carbon to Nitrogen Ratio is 30:1 (by weight). It was vague to me but I finally figured out how it works : All ingredients contain carbon and nitrogen to a ratio as the table below.


Example: 

For 180 gram of corn stalk, there are about 177g carbon and 3g nitrogen (60:1). While for 180 gram of chicken manure , there are about 162g carbon and 18g nitrogen(10:1). So chicken manure is a bigger source of nitrogen than corn stalk. 

    Carbon Rich Ingredients CN Ratio Nitrogen Rich Ingredients CN Ratio
Corn Stalks 60:1 Chicken Manure 10:1
Corrugated Cardboard 600:1 Coffee Grounds 20:1
Dry Leaves 40-80:1 Garden Plants and Weeds 20-35:1
Mixed Paper Products 200-800:1 Grass Clippings 10-25:1
Newspaper 150-200:1 Hay 10-25:1
Pine Needles 60-100:1 Kitchen Scraps(No Dairy, meat, fish) 10-50:1
Sawdusts, weathered 3 yrs 142:1 Rotted Manure 20-50:1
Sawdusts, weathered 2 months 625:1
Straw 50-150:1
Woody Plants trimmings 200-1300:1

Carbon to Nitrogen Ratios Source: Composting for Dummies P. 108 , 2010, Wiley

If you are good at math, you know it's impossible to measure and calculate the weight of each ingredient precisely! Thus, just remember a practical ratio for mixing the carbon-rich and nitrogen-rich ingredients is 3: 1 by volume. This simple rule works, guarantee!


To get the CN ratio right in compost, you can first categorize ingredients into carbon-rich and nitrogen-rich. Then simply use 3:1 in volume to mix them.
 Classify carbon- and nitrogen-rich ingredients. Repeat taking 3 buckets of carbon and 1 bucket of nitrogen and mix them

The steps I found practical are:

1. Classify all your ingredients into two types: Carbon rich and Nitrogen rich ingredients. Set two heaps respectively.

2. Get a bucket. When you take 3 buckets of carbon-rich ingredients, take 1 bucket of nitrogen-rich ingredients and well mix them.

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