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Carbon and Composting: What You Need to Know

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Getting your compost pile to make quality humus relatively quickly is easy if you start with the right mix of brown and green materials.

The microorganisms responsible for decomposing organic material, bacteria, fungi, and actinomyces, get their energy from carbs and use nitrogen for cellular growth. All plant parts are loaded with carbon, and nitrogen is abundant in chlorophyll, the green pigment in plants.

In compiling a compost pile, the gardener must focus on providing the microorganisms with an optimal diet, i.e., balance the ratios of nitrogen-rich green and carbon-rich brown materials.

Given a proper diet and enough water and air, microbes can burn through tons of material in a few months. Successful composting depends on keeping your microbes happy.

Compost Pile Essentials for Great Compost

Making great compost is easy if you stick to the basics listed below:

  • The pile must be at least a cubic yard (meter) to ensure some insulation.
  • You need more brown materials than green. The ideal ratio is 30 parts of carbon for every part of nitrogen.
  • Microbial activity produces heat and is concentrated in the center of the compost pile, the most insulated environment. 
  • Varying internal temperatures are a way of knowing what’s happening and when to do what. 
  • To prevent the microbes from suffocating, turn your compost pile when core temperatures get high enough, incorporating outlying material into the center.
  • The pile must be kept damp throughout but not wet. If your batch gets too wet, you may need to add dry material and turn it (even if core temperatures are low) to prevent the microbes from drowning.

Best Brown Materials

The differing values are factors of freshness. Because nitrogen is volatile, the content in recently harvested products like straw can is  (40:1), but as it dries, it becomes a carbon-rich material (100:1).

The word “organic” refers to materials that are predominantly carbon and free of synthetic materials. Organic materials, including synthetic materials, like pressure-treated wood and gloss paper, are unsuitable for composting. 

MaterialAverage C:N Ratio
Hay15:1 to 30:1
Fall Leaves30:1 to 80:1
Corn Silage40:1
Straw40:1 to 100:1
Corn stalks60:1
Oat Straw70:1
Wheat Straw80:1
Rye Straw82:1
Bark100:1 to 130:1
Wood chips and sawdust100:1 to 500:1
Brush, Wood Chips100:1 to 500:1
Shredded Office Paper150:1 to 200:1
Newspaper400:1 to 800:1
Cardboard500:1

Choosing Green Materials

Not all organic materials are suitable for home composting. Avoid materials that attract scavenger pests, like meat scraps, bones, and fat. 

Below is a list of nitrogen-rich green materials. Food scraps are best fermented in a Bokashi bin before being added to a compost heap.

Green Material List

MaterialAverage C:N Ratio
Fresh vegetable scraps 10:1 to 20:1
Hairy vetch cover crop11:1
Grass clippings12:1 to 25:1
Poultry litter13:1 to 18:1
Alfalfa Hay13:1 
Hay15:1 to 30:1
Cow manure17:1
Legume Hay17:1
Potatoes18:1
Coffee grounds20:1
Rotted Barnyard Manure20:1
Horse manure25:1
Mature Alfalfa hay25:1
Pea Straw29:1

What Are Browns For Compost?

Composting is more about farming with microbes than creating humus. Their introduction to soil boosts your soil’s biodiversity, cation exchange capacity, and root health. 

Adding organic matter to your soil is important because it supports microbial life, boosts plant health and resilience, and improves soil functionality. 

The browns for compost are the primary energy source for these microbes, so they’re important to your microbe farming operations. Great compost is a product of active, well-fed microorganisms.  

Brown Material = Carbon

Brown items provide microbes with the carbon they need, but their addition to your compost pile extends to other functions. 

Structure for Aeration

Browns are generally more rigid than greens and tend to retain their form longer. Browns ensure that compost has a good texture with plenty of air pockets. This helps to create good airflow and provides essential oxygen for microorganisms.

Water Management

Browns, i.e., carbon-rich materials, are generally dry and can help manage the water levels in your compost pile. Your batch is too wet if you can squeeze drops of water out of a handful.

Add more browns to absorb the excess water. There should only be enough water that if you squeeze a handful, only a little water should be visible between your fingers.  

Humus

An excellent example of humus is the soil found on a forest floor. It is the organic matter within soil, a product of microbial decomposition of plants and animals. As trees shed their leaves, animals add fecal matter and urine, and microorganisms interact, humus is formed.

Humus is generally the color of dark chocolate (brown, not black) and is earthy smelling, indicating the presence of actinomycetes. Humus hosts billions of microorganisms essential to soil health. It is the microorganisms in the humus that helps plants access essential nutrients.

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Choosing Carbon-Rich Browns

The most common brown composting materials should be available from your garden. You’ll need to shred these to increase the surface area and speed the composting process up. Composting adds an amazing cycle of life to your garden.

Wood from Tree Pruning and Hedge Trimmings

Branches are a great way to add structure to your pile, increasing airflow and drainage while feeding your microbes.

Layers of shredded wood added to your compost bin must not be too thick, allowing organisms access to greens.

Wood Shavings and Chips

Wood chips are generally obtained from a woodwork firm and are great for absorbing excess water. Beware of chipped wood boards, as these contain chemicals to help them bond. Avoid using shavings from pressure-treated wood.

Excessively fine sawdust tends to mat, so mix it with shredded leaves. Pet bedding sawdust (with added excrement) will help you make great compost. 

Wood Bark

The bark is a great brown, especially if used for mulch. Just be aware that not all wood or bark is good for composting, as some (like the cedar) have fungicidal properties.

The bark should be shredded to increase the surface area and speed of decomposition. Add a reasonable amount of greens to boost bioactivity.

Paper Products

Avoid cardboard with a plastic film or gloss-printed magazines. Wetting your paper before adding it to your compost bin is always good. Cardboard has a high carbon-to-nitrogen ratio and is a great brown material (see table above). 

Most processed paper and cardboard are not very rich in nutrients. It adds good structure and carbon to compost bins when shredded, but I recommend using it sparingly. 

Paper products make a great composting option, but their high carbon content per volume is deceptive, and adding too much will slow the process down considerably. 

Shredded cardboard is a great composting option during summer when browns are harder to come by. Another solution for summer is storing shredded, dry leaves to use when grass clippings are abundant.

Fall Leaves

Dry leaves are an excellent brown but must be shredded before being added to compost bins. They are also great for leaf mold manufacturing. 

Dead leaves are generally abundant in late fall, covering the ground under deciduous trees. Shred leaves you to gather in early winter and find some way to dry them before storage.

Store fallen leaves in plastic bags, removing excess air to make them more compact. Use them as mulch or leaf mold or be added to compost when grass clippings are abundant. 

An electric leaf shredder is a great tool, but you can achieve the same results if you run over leaf piles several times with a mower. Shredded leaves have a large surface area for fungi to work on and a better texture for good air circulation.

Any product with high lignin (fibrous material in wood) content is resistant to degradation by bacteria, a task best suited for fungi. Fungi populations can be boosted by an abundance of proteins like kitchen scraps.

Pine Needles

Pine needles are a great source of carbon and are low in moisture. It is often claimed that pine needles are great for acid-loving plants, but there is empirical proof that this is not the case.

Poor aeration in the composting process is caused by composting materials that clump together, like pine tree needles and unshredded leaves. If your bins smell bad, it is usually a sign of a lack of air during composting. 

Anaerobic microorganisms produce odorous gas like sulfur dioxide and methane. As long as pine tree needles are less than 10% of the total materials, they will not prevent you from creating a great compost. 

If you add air-inhibiting materials, expect a smelly, slimy mess in your pile.

Hay and Straw

Hay is a finer grass substance, while straw is rich in cellulose and lignin and, therefore, more rigid. The lignin and cellulose are resistant to bacterial decay, needing fungi to do the initial work. You can boost fungi populations by adding proteins like kitchen scraps. 

In the same way, you can boost bacterial activity by adding carbohydrates like molasses to the compost pile. While hay and straw are great brown materials, hay tends to degrade faster.

Straw is a great brown material for improving the aeration of your compost pile. It is tough, breaks down slowly, and is generally sourced externally. Other sourced brown materials may be nut shells, sawdust, and wood shavings.

For a healthy compost mix for your garden, ensure your hay or straw hasn’t been treated with herbicides or pesticides.

Cornstalks, Husks & Cobs

Rigid hard materials like corn stalks, cobs and husks are slow at composting but a great carbon source. Give your composting microorganisms a helping hand by chopping them up and mixing them with plenty of green stuff.

Wood Ashes 

Ensure you only compost wood ash, not coal ash, which can contain large amounts of sulfur. Barbecue wood charcoal is great for adding to your garden but is of little use in your compost bin.

In Closing

Healthy, finished compost is essential for a healthy garden. It is not an elective soil enhancer. Compost is imperative to root health and optimal photosynthesis. Getting your mix of greens and browns right determines the speed and efficacy of the process. I hope this article helped.