Carbon To Nitrogen Ratio For The Perfect Compost

An Introduction to the Essentials of Composting

The secret to generating nutrient-dense, earth-friendly compost lies in understanding the relationship between carbon (C) and nitrogen (N), which play an integral role in the decomposition process.

The Alchemy of Carbon and Nitrogen

Organic matter relies on the synergy between carbon and nitrogen: integral components of all living organisms. This pivotal balance is known as the Carbon-to-Nitrogen ratio (C:N ratio). When composting, carbon provides energy while nitrogen assists in protein production, thus fostering a thriving environment for decomposition.

The key to superior composting lies in maintaining an optimal C:N ratio, preferably around 25 to 30 parts carbon to 1 part nitrogen (25-30:1). This ratio ensures a speedy decomposition while creating a fertile, aromatic compost. An excess of carbon could decelerate the decomposition process, while an excess of nitrogen may result in an unpleasantly odorous pile.

Understanding ‘Browns’ and ‘Greens’

In the quest for perfect compost, categorizing organic materials as “browns” and “greens” can simplify the process significantly. Browns represent materials rich in carbon, while greens signify those abundant in nitrogen.

Browns – Powerhouses of Carbon

Common brown materials with their respective C:N ratios

High Carbon Items C:N Ratio
Apple pomace 48:1
Bark 100-130:1
Cardboard (Shredded) 350:1
Corn stalks 70:1
Fruit Waste 35:1
Leaves / Foliage 40-80:1
Paper (Shredded) 175:1
Peanut shells 35:1
Straw 75:1
Wood and Sawdust 300-700:1
Wood chips 400:1

Greens – The Nitrogen Enrichers

Common green materials with their respective C:N ratios

High Nitrogen Items C:N Ratio
Alfalfa 12:1
Clover 23:1
Coffee grounds 20:1
Crab / Lobster Waste 7:1
Fish waste 7:1
Food waste 15-20:1
Garden waste 30:1
Grass clippings 19:1
Hay 25:1
Manure: Cow 20:1
Manure: hen 10:1
Manure: hen litter 15:1
Manure: Horse 25:1
Manure: sheep 25:1
Seaweed 19:1
Soybean meal 15:1
Vegetable scraps 20:1
Weeds 30:1
Wood ash 25:1

Understanding Ratios – an analogy

Picture a large jar filled with 175 red marbles and just 1 blue marble. This jar is like shredded paper which is rich in carbon (red marbles) but has very little nitrogen (blue marble).

Now, imagine a second jar that holds 19 red marbles and 1 blue marble, representing grass clippings. In this jar, there are fewer red marbles, meaning there is more room for blue marbles or more nitrogen compared to the shredded paper.

To put it simply, the larger the first number in the ratio (the red marbles) compared to the second number (the blue marbles), the less nitrogen the material has.

Carrying forward our marble analogy, the goal in composting is to create a mix of red and blue marbles in a jar where there are between 25 and 30 red marbles (carbon) for every 1 blue marble (nitrogen).

To achieve this, we might need to mix jars with different ratios together. If one jar has too many red marbles (high carbon source like shredded paper), we could add some from a jar that has more blue marbles (high nitrogen source like grass clippings).

This way, by carefully combining different jars, or in composting terms, different types of organic waste, we can achieve our desired mix that has the perfect balance of 25-30 red marbles to 1 blue marble, or a 25-30:1 Carbon-to-Nitrogen ratio.

Mastering the Perfect Compost Recipe

Ingredients for composting rarely possess the ideal C:N ratio of 25-30:1, so blending various materials is essential to achieve the perfect compost recipe. High C:N ratios can be balanced by adding greens like grass clippings or manures, while low ratios can be enhanced with the addition of browns such as paper, dry leaves, or wood chips.

Despite minor odours, some garden enthusiasts opt to maintain a slight surplus of nitrogen in the compost pile to ensure continuous and efficient decomposition—a testament to the adage that the pile must always be “cooking.”


Jonathan Gaze

Content Editor

Hello there! I’m Jonathan Gaze, Content Editor for Harry Rufus.

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