Compost 101

Compost 101


Welcome to Composting 101! Today, we'll explore the different types of compost, the importance of carbon to nitrogen ratios, and several methods of creating compost on your farm or garden. 

When we talk about compost, we often classify each type of compost by the method used to make it. This is of course very important and we will discuss a number of those methods below. However, it’s important to step back for a minute and think about composting with intention. How do we want to use the compost? What is our goal for this compost? 

There are four different types of compost, if we classify them by how we want to use them.

Section 1: The Four Types of Compost 

1.1 Inoculating Compost

Inoculating compost, like the Johnson Su bioreactor, is primarily used for its microbial content. It introduces beneficial microbes to your soil, boosting plant health and growth.

1.2 Fertilizing Compost 

Fertilizing compost, such as compost from dairy or chicken manure, is high in NPK value. It acts as a powerful, nutrient-rich fertilizer for your plants.

1.3 Nutritional Compost 

Nutritional compost offers a balance of microbes, minerals, and organic matter. It improves soil structure and provides a steady supply of essential nutrients to your plants.

1.4 Mulching Compost 

Mulching compost is primarily used as a soil cover, providing carbon and protecting the soil from erosion and moisture loss.

Section 2: Critical Factors in Compost 

2.1 Carbon to Nitrogen Ratio

The carbon to nitrogen ratio, or C:N ratio, is a critical aspect of composting. A balanced C:N ratio ensures efficient decomposition, reduces odor, and promotes healthy microbial growth. 

The C:N ratio is a measure of the balance between carbon-rich (carbonaceous) and nitrogen-rich (nitrogenous) materials in the compost pile. This balance is crucial because microorganisms, particularly bacteria and fungi, utilize carbon as a source of energy and nitrogen for the synthesis of proteins and other cellular components. The ideal C:N ratio for efficient composting is typically between 25:1 and 30:1.

Effects on Composting Speed and Temperature

When the C:N ratio is within the optimal range, microbial activity is high, leading to rapid decomposition and an increase in temperature. The heat generated by the microorganisms can reach between 55°C (131°F) and 65°C (149°F), effectively killing weed seeds and pathogens while accelerating the composting process. In contrast, a C:N ratio that is too high (excess carbon) or too low (excess nitrogen) can slow down the decomposition process and produce undesirable outcomes.

A high C:N ratio (> 30:1) can result in slow decomposition and low temperatures, as the microorganisms become carbon-limited, leading to insufficient energy for rapid growth and reproduction. This may result in an extended composting period and a final product that is not fully decomposed.

A low C:N ratio (< 25:1) can cause excessive nitrogen release as ammonia, creating an unpleasant odor and a loss of valuable nitrogen. Moreover, excess nitrogen may lead to overly rapid microbial growth, consuming available oxygen and creating anaerobic conditions that can further slow decomposition and produce foul-smelling compounds.

Sources of Composting Input Materials and Their Impact on the C:N Ratio

Various input materials can be used in composting, each with different C:N ratios. Striking the right balance is essential to achieve optimal composting conditions.

Carbonaceous materials, also known as "browns," are typically dry and include items such as dried leaves, straw, wood chips, sawdust, and shredded paper. These materials are high in carbon and low in nitrogen, contributing to an increase in the C:N ratio.

Nitrogenous materials, also known as "greens," are usually moist and include items such as grass clippings, food scraps, coffee grounds, and animal manures. These materials are high in nitrogen and low in carbon, contributing to a decrease in the C:N ratio.

To maintain the optimal C:N ratio in the compost pile, it is essential to combine carbonaceous and nitrogenous materials in appropriate proportions. This usually involves adding more browns than greens, as carbonaceous materials tend to be less dense and contain less available carbon per unit volume.

2.2 Oxygen

Oxygen is a vital component in the composting process, as it supports the growth and metabolism of aerobic microorganisms that drive the decomposition of organic materials. These aerobic microbes, which include various species of bacteria and fungi, require oxygen to break down complex organic molecules into simpler compounds, ultimately transforming the raw materials into nutrient-rich compost.

A well-aerated compost pile facilitates the rapid growth and reproduction of aerobic microorganisms, leading to increased heat generation and accelerated decomposition. Higher temperatures in the compost pile not only speed up the breakdown of organic matter but also help eliminate pathogens and weed seeds, ensuring a safe and effective end product.

In contrast, when oxygen levels are low, the decomposition process slows down, and anaerobic microorganisms begin to dominate. These anaerobic microbes break down organic matter through fermentation, producing compounds such as methane, hydrogen sulfide, and ammonia, which can cause unpleasant odors and hinder the effectiveness of the compost as a soil amendment.

Maintaining proper oxygen levels in the compost pile is essential to promote efficient decomposition and avoid the problems associated with anaerobic conditions. There are several strategies for ensuring adequate aeration throughout the composting process:

Turning the pile: Periodically turning the compost pile helps to mix the materials and reintroduce oxygen into the system, promoting aerobic decomposition. This can be done manually with a pitchfork or mechanically with specialized equipment.

By understanding the critical role of oxygen in composting and implementing strategies to maintain proper aeration, composters can support the growth of beneficial aerobic microorganisms, accelerate the decomposition process, and produce high-quality compost that contributes to sustainable agriculture and soil health.

2.3 Moisture

Moisture is another essential factor in the composting process, as it directly influences the activity and survival of microorganisms responsible for decomposing organic materials. Adequate moisture is necessary for the metabolic processes of these microbes, as it helps dissolve nutrients, transport them across cell membranes, and maintain the overall structure and function of the microbial community.

The optimal moisture content for composting is generally between 40% and 60%, which ensures a suitable environment for microbial growth without causing excessive compaction or limiting oxygen availability. A well-balanced moisture level in the compost pile promotes efficient decomposition, reduces the risk of unpleasant odors, and ultimately results in a high-quality, nutrient-rich compost product.

Too little moisture can impede microbial activity, as insufficient water can cause the microbes to become dormant or die. When water availability is limited, the decomposition process slows down, and the compost pile may fail to generate enough heat to break down the organic matter effectively. In such cases, adding water or incorporating moisture-rich materials, such as food scraps or grass clippings, can help restore the proper moisture balance.

Conversely, too much moisture in the compost pile can also be problematic, as excess water can displace oxygen in the air spaces between particles, leading to anaerobic conditions. Under these circumstances, the decomposition process becomes less efficient, and undesirable compounds, such as methane and hydrogen sulfide, are produced, causing foul odors. To address excessive moisture, incorporating dry, absorbent materials like straw, wood chips, or leaves can help soak up excess water and restore the optimal moisture balance.

Managing moisture in the compost pile involves regular monitoring and adjusting the input materials as needed. In addition to turning the pile to improve aeration, protecting the compost pile from heavy rainfall or covering it with a tarp can help maintain consistent moisture levels. By understanding the importance of moisture in composting and employing strategies to manage it effectively, composters can support the growth of beneficial microorganisms, facilitate efficient decomposition, and produce high-quality compost that contributes to sustainable agriculture and soil health.

Section 3: Composting Methods on the Farm 

3.1 Traditional Windrow Composting 

Traditional windrow composting uses horse manure and other organic materials, piled into long rows called windrows. This method requires regular turning for aeration and efficient decomposition.

3.2 Johnson Su Bioreactor Compost 

The Johnson Su bioreactor is a composting method that focuses on fostering beneficial microbial growth. It involves layering organic materials inside a mesh tube, with little to no turning required.

The Johnson-Su bioreactor is an innovative composting system developed by Dr. David Johnson and his wife, Hui-Chun Su, as a means to create compost rich in fungal and bacterial diversity. This static, aerobic composting method is designed to produce a stable, nutrient-dense, and biologically diverse compost while minimizing the labor and energy inputs typically associated with traditional composting techniques.

Unlike traditional composting methods that require frequent turning to maintain aeration, the Johnson-Su bioreactor uses a static approach that relies on passive airflow. The bioreactor is constructed using a combination of materials, such as wire mesh or hardware cloth, to form a cylinder approximately 4-5 feet tall and 4 feet in diameter. The cylinder is filled with alternating layers of carbonaceous ("brown") and nitrogenous ("green") materials, with perforated PVC pipes placed vertically throughout the pile to facilitate passive airflow and ensure adequate oxygen supply to the microbes.

One of the key features of the Johnson-Su bioreactor is its emphasis on fostering a diverse and robust microbial community. By promoting both bacterial and fungal growth, the resulting compost contains a wide range of beneficial microorganisms that contribute to improved soil health and plant growth. The static nature of the Johnson-Su bioreactor, combined with a longer composting period (typically 9-12 months), allows for the development of fungal hyphae and a more complex, interconnected microbial network.

The Johnson-Su bioreactor offers several advantages over traditional composting methods. Due to its static design and passive aeration, the system requires minimal labor and energy inputs, making it an attractive option for small-scale or resource-limited farmers. Additionally, the focus on developing a diverse and biologically active compost product can lead to significant improvements in soil health, nutrient cycling, and disease suppression, ultimately contributing to more sustainable agricultural practices.

3.3 Vermicompost 

Vermicomposting uses worms to break down organic matter into nutrient-rich, humus-like material. This method can be done in small bins or large-scale setups.

Vermicomposting is a biological process in which earthworms, primarily red wigglers (Eisenia fetida), are used to decompose organic waste materials, transforming them into a nutrient-rich, organic soil amendment known as vermicompost or worm castings. This process not only helps recycle organic waste but also produces a valuable resource for enhancing soil fertility and plant health.

Earthworms consume organic materials, breaking them down in their digestive systems, and excrete nutrient-rich castings, which contain a variety of essential plant nutrients, such as nitrogen, phosphorus, potassium, and micronutrients. In addition to these nutrients, vermicompost is also rich in beneficial microorganisms, such as bacteria, fungi, and protozoa, which play a crucial role in nutrient cycling, soil structure improvement, and disease suppression.

Vermicomposting can be done on various scales, from small household systems to large commercial operations. The process typically involves setting up a worm bin or bed with bedding material, such as shredded paper, coconut coir, or peat moss, and adding the red wigglers. Organic waste materials, such as fruit and vegetable scraps, coffee grounds, and eggshells, are then added to the bin, providing a food source for the worms. It is essential to maintain proper moisture and temperature levels within the bin to support worm activity and reproduction.

One of the advantages of vermicomposting over traditional composting methods is the relatively rapid decomposition of organic materials, which can be attributed to the combined action of earthworms and microorganisms. Vermicompost is also considered more nutrient-dense and biologically active than traditional compost, providing a range of benefits when used as a soil amendment or as a component of potting mixes. These benefits include improved soil structure, increased water retention, enhanced nutrient availability, and greater resistance to pests and diseases.

3.4 Anaerobic Compost 

Anaerobic composting is a low-maintenance method that relies on microorganisms that thrive in oxygen-deprived environments. This method is often used for processing food waste.

Anaerobic composting is a decomposition process that occurs in the absence of oxygen, relying on the activity of anaerobic microorganisms to break down organic waste materials. While aerobic composting is often considered the more common and preferred method, anaerobic composting can also be an effective way to recycle organic waste and produce valuable soil amendments under specific conditions.

In anaerobic composting systems, the organic waste is typically placed in a sealed container or enclosed environment, limiting the exposure to oxygen. This creates an environment that favors the growth of anaerobic microorganisms, such as anaerobic bacteria and archaea, which use alternative electron acceptors, such as sulfate, nitrate, or carbon dioxide, instead of oxygen to break down organic matter. The anaerobic decomposition process generates various end products, including methane, hydrogen, carbon dioxide, and volatile organic compounds.

Anaerobic composting can offer several advantages over aerobic composting. Firstly, it requires less labor and maintenance, as there is no need for turning or regular aeration. This makes it an attractive option for individuals or communities with limited resources or labor availability. Secondly, anaerobic composting can handle a wider range of organic waste materials, including those with high moisture content or high-fat content, which can be challenging to compost aerobically.

However, there are also some drawbacks to anaerobic composting. The decomposition process tends to be slower than in aerobic systems, often taking several months to over a year to produce stable compost. Additionally, the end products of anaerobic decomposition, such as methane and volatile organic compounds, can contribute to greenhouse gas emissions and create unpleasant odors. Proper management and containment of these gases are crucial to minimize environmental impacts and maintain good community relations.

One notable example of anaerobic composting is the bokashi method, which originated in Japan. Bokashi composting involves fermenting organic waste materials in an anaerobic environment, typically using a specialized inoculant of beneficial microorganisms, such as lactic acid bacteria, yeasts, and phototrophic bacteria. The bokashi process not only helps break down organic materials but also preserves nutrients and produces a nutrient-rich, fermented pre-compost that can be further composted aerobically or added directly to the soil.

3.5 Static Aerated Compost 

Static aerated composting involves using pipes to provide aeration to compost piles, eliminating the need for turning. This method speeds up decomposition while reducing labor and machinery requirements.

Static aerated composting is a composting method that employs forced aeration to maintain aerobic conditions within the compost pile without the need for frequent turning. This method combines the benefits of aerobic decomposition with reduced labor and energy inputs, making it an attractive option for large-scale operations or those seeking to minimize the time and effort involved in compost management.

The process of static aerated composting involves constructing a compost pile or windrow with a balanced mix of carbonaceous and nitrogenous materials. A perforated aeration system, such as PVC pipes or specialized equipment, is installed throughout the pile to deliver oxygen directly to the core of the compost. By forcing air into the pile, the system ensures that aerobic microorganisms have a continuous supply of oxygen to support their metabolic processes, enabling efficient decomposition and heat generation. The increased temperatures within the pile also help to kill pathogens and weed seeds, enhancing the quality of the final compost product. Monitoring and adjusting the moisture levels within the pile are essential to maintain optimal conditions for microbial activity and decomposition.

There are several advantages to static aerated composting. The primary benefit is the reduction in labor and energy requirements compared to traditional turned composting systems. By eliminating the need for regular turning, static aerated composting can save time and resources, making it more cost-effective for large-scale operations or those with limited labor availability. Additionally, the forced aeration system promotes a faster decomposition process, often resulting in a finished compost product within 30 to 60 days, depending on the materials used and environmental conditions. Furthermore, the controlled aeration and relatively undisturbed nature of the pile can reduce the potential for odor issues and greenhouse gas emissions, contributing to a more environmentally friendly composting process.


Composting is a sustainable and effective way to recycle organic matter, improve soil health, and provide nutrients to your plants. By understanding the different types of compost and methods, you can choose the best approach for your farm or garden. 

Happy composting!