How To Get The Right Carbon To Nitrogen Ratio In Your Compost

A plant in a terracotta pot with kitchen scraps.

Every ingredient in your compost pile consists of a significant quantity of carbon (C) and a minor amount of nitrogen (N), and the balance of these two elements in an organism is called carbon to nitrogen ratio (C: N ratio).

Water, air, carbon, and nitrogen are the most important among the many elements required for microbial decomposition.

But did you know that carbon is the primary source of energy and the basic building block of the microorganisms’ mass of cells? Yes, it is.

Nitrogen, on the other hand, is necessary for their protein requirements, genetic materials like nucleic and amino acids, enzymes, and cell structures.

The use of carbon-to-nitrogen ratio for each of your compost ingredients is the most efficient way to provide the optimal nutrient your plants require.

The compost pile requires a correct proportion of carbon for energy and nitrogen for protein production to achieve its optimal performance.

And according to the composts scientists, the fastest way to produce fertile, sweet-smelling compost is to maintain an ideal C: N ratio, which is around 25-30 parts of carbon to 1 part of nitrogen.


How To Measure Carbon to Nitrogen Ratio In Your Compost Mix


#1 – Find the approximate percentage of carbon and nitrogen in your ingredients

To measure the carbon-to-nitrogen of your compost pile, you have to first find the approximate percentages of carbon and nitrogen in your ingredients.

This method will give you an idea of how to adjust the proportions of your ingredients to get your composts finished more quickly.

#2 – Get the carbon value by following the formula

Here’s an example of how to calculate and get the C: N ratio quickly.

Get the total carbon value of your ingredients by following this formula.

  • 50 pounds of non-legume hay
  • 10 pounds of kitchen scraps
  • 2 pounds of coffee grounds 

  • First Step: Multiply the number of parts (weight) of your ingredients to its corresponding carbon value on the chart below.

50 lbs hay x 40% C = 20 lbs. C

10 lbs kitchen scraps x 10% C = 1 lb. C

2 lbs coffee grounds x 25 % C = 0.5 lb. C

  • Second Step: Add up the carbon totals for all the ingredients.

20 + 1 + 0.5 =21.5 Total Carbon Value

#3 – Follow the same formula to get the nitrogen value of your ingredients
  • First Step:

50 lbs hay x 1% N = 0.5 lb. N

10 lbs kitchen scraps x 1% N = 0.1 lb. N

2 lbs coffee grounds x 1 % N = 0.02 lb. N

  • Second Step:

0.5 + 0.1 + 0.02 = 0.62 Total Nitrogen Value

#4 – Divide the carbon totals by the nitrogen totals to get the C: N ratio
  • 21.5/0.62= 34.7 parts of carbon to 1 part of nitrogen is the cumulative C: N ratio of your compost recipe. 
#5 – Achieve the C: N ratio between 25 and 35 to make the most of it
  • Your pile will thoroughly decompose if you find the total C: N ratio between 25 and 35.
  • If you find the ratio higher or lower than the ideal one, adjust the proportions of ingredients.
  •  It is necessary to achieve the range of 25 to 35 of carbon to every part of nitrogen. 

Note: This calculation isn’t perfect, but it’ll get you close enough to get sensible results. You can also try some minor adjustments to achieve the output desired.

Carbon and Nitrogen  Content of Common Compost Ingredients

Material

% Carbon

% Nitrogen

Alfalfa Pellets 40.5 2.7
Alfalfa Hay 18 1
Blood meal 43 13
Cottonseed meal 42 6
Corn stalks 80 1
Sandy loam (fine) 7 1
Soybean meal 42 6
Legume hay, dry 40 2.0-2.5
Non-legume hay, dry 40 1.0-1.5
Humus 10 1
Fresh manure, cow 12-20 0.6-1.0
Fresh manure, horse 20-35 0.5-1.0
Fresh manure, laying chickens 10.5-20 1.5-3.0
Fresh manure, broiler chickens 20-32.5 1.3-2.0
Food Scraps 15 1
Wheat or oat straw, dry 48 0.5
Grass clippings, fresh 10-15 1-2
Fallen leaves 20-35 0.4-1.0
Newspaper or cardboard, dry 40 0.1
Wood chips or sawdust 25-50 0.1
Coffee grounds 25 1.0
Vegetable wastes, fresh, leafy 10 1.0
Vegetable wastes, starchy 15 1.0
Kitchen scraps 10-20 1-2
Fruit wastes 8 0.5
Seaweed, fresh 10 1.0
Weeds, fresh 10-20 1-4
Chicken manure 10 1
Horse manure 27 1
Solid cattle manure (light bedding) 20 1
Solid cattle manure (heavy bedding) 40 1
Coffee grounds 20 1
Plant trimmings 200-1300 1
Sawdust (weathered 2 months) 625 1
Pine needles 60-110 1

Note: The C: N ratio above are only guidelines, and understand that different types of materials differ in carbon and nitrogen content.


The Importance of C:N Ratio To The Soil

Two hands cup the heart formed plants in the soil.
Image by: aprio.com

The carbon to nitrogen ratio (C: N) is a ratio of the weight of carbon and nitrogen in a substance.

Contrary to the belief of many, getting the right C: N ratio is not about making the compost. It is about reaching the appropriate C: N ratio that is essential if you want to speed up the decomposition, with the help of microorganisms in the soil. 

However, it is the interaction of carbon and nitrogen to the microorganisms that anticipates how fast the breakdown works.

The Imbalance C: N Ratio May Result In The Following Issues

  • The excess of carbon will result in a slow compost decomposition.
  • The excess of nitrogen can cause the element to evaporate and be lost as ammonia gas, causing you to end up with a foul-smelling pile.

A low C: N ratio will result in fast exhaustion of carbon making the harmful bacteria dominate the soil.

As we already know, carbon is not only beneficial to the microorganisms, but it also preserves the nutrients and retains water the plants will utilize later.

The shortage of carbon may also result in the loss of mineralized nitrogen through leaching.

Another scenario that is not beneficial to your soil is nitrogen deficiency. This deficiency can make the soil organisms use the available nitrogen reserve for the plants to supply their bodily requirements.

Nitrogen immobilization is when the microorganisms will consume all the available nutrients instead of releasing them for the plants to use.

Microorganisms that lack nitrogen are also on the brink of death which can result in a delay of decomposition.

To balance the diet of digesting microorganisms in your compost, you will need about 30 parts of carbon for every part of the nitrogen they consume.

Digesting microorganisms only use a sufficient amount to meet their needs. The excess of nitrogen will evaporate and be lost in the form of smelly ammonia gas. Know that nitrogen is too valuable for plants to allow it to escape into the air.

Since the C: N ratio of the soil has a significant effect on the nutrient the plants require, it is necessary to understand these particular ratios.

Microorganisms in the soil need to acquire sufficient carbon and nitrogen from the environment. 

They burn carbon to acquire energy. However, not all the carbon in the soil in which the microbes consume remains in its body. A certain amount is lost as carbon dioxide when they breathe.

For the microorganisms to live and help generate the ample nutrients your plants need, they require a diet with at least a C: N ratio of 24:1. The microbes will use the 16 parts of carbon for energy, while the other eight are for maintenance.

The Rule Of Thumb To Determine Your Organic Materials

  • Organic material with a C: N ratio smaller than 30:1 is GREEN
  • Organic material with a C: N ratio larger than 30:1 is BROWN

The Impact of Microorganisms to the Soil

A host of worms in the soil.

Fertile soil has three interacting components, which are physical, chemical, and biological fertility.

Physical fertility refers to the soil attributes such as the soil structure, the texture, the water absorption and the capacity to retain moisture, and the root infiltration.

Chemical fertility also refers to the presence of nutrients and chemical conditions like acidity, salinity, and alkalinity that may be harmful to the plants.

Biological fertility refers to the microorganisms that interact with the other elements in the soil. These organic matters that live under the ground play a lot of significant functions for the cycles of nutrients and carbon.

Among the three fertility components, the biological component, including the rich diversity of organisms is the most complex and the least well-understood.

However, the soil microbial communities are the primary drivers in the ecological process which include nutrients and carbon recycling, elimination of contaminants, and eradication of soil-borne diseases.

These microbes are also fully involved in advantageous and vital interrelationships within the soil and plants.

Soil organisms do not exist in isolation, and they have distinct characteristics and different functions in the soil they live in. They too love to interact, and these interactions affect soil fertility.

They are both elements and generators of soil organic carbon. An element that locks carbon into the soil for some time.

An abundance of soil organic carbon will not only enhance soil fertility and water retention capacity, but it also lessens the atmospheric greenhouse that causes climate change.

Check out the summary once more to help you understand clearly the logic behind the C: N ratio.

  • The C: N ratio is an essential factor determining how fast the soil organisms can break down the organic material in your pile.
  • Just as we burn carbohydrates to supply energy and protein to build and repair our human bodies, the organisms in compost use carbon for energy and nitrogen for protein for their cell structures.
  • The average of 30: 1 is the optimal proportion of the carbon-to-nitrogen ratio the bacteria require.
  • Providing a balanced diet of 30:1, the organisms in the soil can disintegrate the organic materials in the compost pile quickly.

Overall, soil microorganisms play a significant role and are of prime importance in the process of decomposing organic matter, recycling nutrients, and fertilizing the soil.


The Best Source of Carbon and Nitrogen For Your Composts


Green Composting Materials

The nitrogen materials known as greens provide the bodybuilding proteins for digesting microorganisms. The following substances are the best source of nitrogen for your compost pile.

1) Kitchen Scraps

The kitchen scraps are a great addition to your compost pile. Adding them to your pile can be a great way to help the environment too.

  • Coffee grounds and used filters
  • Condiments and sauces
  • Corncobs
  • Cut flowers
  • Eggshells
  • Fruit pits
  • Fruit rinds and cores
  • Nutshells
  • Shells from shellfish
  • Stale bread and grain products
  • Tea and tea bags
  • Vegetables (raw or cooked)

Tip: Eggshells, nutshells, and shellfish shells are slow to decompose. You can first crush them in a grinder before adding to your compost pile to help speed the decomposition process.

2) Grass Clippings

It is necessary to mix grass clippings with brown materials or dry them a few hours by spreading under the sun. Doing this before mixing into your heap will avoid them turning smelly and slimy. The unpleasant smell usually occurs if you leave them in big piles or layered too thickly.

3) Vegetables And Plant Leaf Trimmings

Garden scraps after the finished producing season are also a great addition to your composts. You can also add some leafy trimmings from landscapes, shrubs, and trees. You can toss them all into the pile to recycle their nitrogen content.

4) Weeds Foliage

Weed leaves are also an excellent source of nitrogen. You can bring back those nutrients they took off from your plants by adding them to your pile.

5) Domestic Animal Manure

Domestic animal manures are safe to add to your compost pile. Plants require nitrogen, phosphorus, potassium, boron, iron, and zinc. These are several elements you can find from animal manures.

Warning: Animal manure should be at least six months old if you’re considering using them directly in your garden. Like undiluted mushroom compost, fresh manure contains high concentrated nitrogen that can burn not only the roots of your plants but most especially the tender young seedlings. It prevents seed germination too.

You can also utilize fresh manure the following two ways:

  • Blend it sparingly with other dry ingredients and allow it to dry before adding them to your pile.
  • You can also spread them across garden beds in the fall. Allow it to rot during winter months.

Reminder: Always remember to wear gloves, shoes, and a mask when collecting fresh manure or spreading them across your garden beds. Make sure to wash your hands thoroughly and scrub under your nails right after handling the manure.


Brown Composting Materials

Dried leaves gathered in the ground.

The success of composting depends on the right ingredients. Brown materials are the primary source of energy for the digesting microorganisms.

1) Leaves

Leaves are proven to be an excellent ingredient for your compost. People living in areas with bounty autumn leaves are privileged to make the most of it. You can also ask some neighbors to pass their leaves, and many will do the raking if you cart the piles away from them.

Living green leaves are referred to as green materials, while dried leaves are considered brown materials.

Dried leaves contain an ample amount of nutrients and a great source of carbon for your plants.

However, laying leaves that aren’t shredded in your compost tend to mat them together, hindering sufficient aeration of the pile. To avoid such an issue, shredding them is more beneficial before adding to the heap.

The following leaves need special attention if you wish to consider them in your pile.

  • Walnut leaves

Walnut leaves consist of properties that can restrict the growth of several plants. Either you have to compost thoroughly or not use them at all.

  • Oak leaves

It usually takes a long time for oak leaves to break down due to their acidity and high levels of tannin. They are excellent for acid-loving plants, but breaking down will take much longer than other leaves.

If you live in an area where oak leaves are abundant and would love to utilize them in your compost, you can keep them in a separate pile and use them on acid-loving plants.

  • Waxy leaves

Plants with waxy leaves like holly, laurel, rose, pine and rhododendron take longer to break down. Composting them separately usually produces the best results.

2) Hay (Legume and Non-Legume)

All types of hay can be an excellent addition to your compost.

3) Straw

Straw provides a plentiful amount of carbon but lesser nitrogen. It disintegrates slowly too, making it an excellent addition to areas with compacted soil. So, if you find remaining particles in your finished compost, you can use them to help loosen the clayey soil structure.

4) Paper and Cardboard

Paper is an excellent addition to your compost pile. However, it is always best to shred newspapers, bills, paper towels and tissues before tossing them to your heap.

It is necessary to rip up stiff cardboard into small pieces before adding them into your pile to help speed up the process.

Adding glossy and highly colored papers that might contain toxic heavy metals is not recommended.

5) Eggshells

Eggshells contain calcium that is beneficial to your plants, making it a great addition to your compost.

However, eggshells usually take much longer to break down. Adding already powdered eggshells is a smart idea if you wish a quick decomposition.

Note: Adding the whole eggs is not advisable. It can emit foul odors, resulting in flies and some invaders like rodents that may affect the breakdown process of your pile.

6) Tea Bags

You can add both black and herbal teas in your compost, whether it is loose leaves or in bags.

7) Sawdust

Sawdust contains lesser amounts of nitrogen and is very slow to break down. You can use it in thin layers or thoroughly incorporate them with green materials like grass clippings and kitchen scraps.

Warning: Be careful not to add sawdust from pressure-treated wood to your compost. The chemical treatment on the wood can leach arsenic into the soil when used for making raised beds, playground equipment, and compost bins, which is not beneficial to your plants.

8) Wood Ashes

Wood ashes are also an excellent source of calcium and potassium, but they too are very alkaline. Using them sparingly is also advisable to avoid high pH levels that will restrict microbial functions.

Charcoal bricks also take time to disintegrate, making it smart to avoid adding them to your compost pile.

In addition to that, ashes generated from commercially made fire logs contain wax and petroleum derivatives. These components can also do more harm than good if you add them to your pile.


Final Thoughts on How To Get The Right Carbon to Nitrogen Ratio In Your Compost

To meet the ideal C: N ratio is an efficient way to speed up the composting process.

To determine the visible relationship between the high nitrogen-content materials known as greens and the high carbon considered as browns can help a lot in your composting method.

Adjusting the numbers to achieve the ideal ratio will also give more sensible results if you work on weight rather than a volume system.

To become familiar with how the C: N ratio works, be curious and experiment for a while. Also, be acquainted with the amount of materials you used while formulating like a chef adjusting the ingredients for your recipe.

Also, you will gradually find out what your pile needs as you take note of the temperature it reaches, and the quality of the finished compost based on your assessment.

Have you tried composting based on the ideal C: N ratio?  Is there anything you would like to share based on your experience? Please don’t hesitate to share them in the comment section below.

About Benita Abucejo

Hi there! My name is Benita Abucejo. What can I say? I truly love spending my days in the outdoors, specifically in the garden. Gardening has always been a strong passion of mine since I was a little girl. It has brought me so much joy and happiness that it is definitely safe to say that I will be a gardener for life. For a period of time, I was able to work with people who are into home gardening and I found it to be quite beneficial to my physical health, as well as my mental well-being. Here at Seasonal Preferences, I am going to share with you my experience and ideas so that you can fulfill yourself with the same satisfaction and happiness. Of course, if you have ideas, I would love to hear those as well! Being creative in the garden can really be quite fascinating so let's share our experiences and be the best gardeners we can be. With that being said, thank you for dropping by and please leave me a comment on one of my posts if you would like to get in touch!

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