How Does Compost Work?

The Science Behind Composting: How Does Compost Work?

Everything organic will inevitably decay at some point of time. This is thanks to the trillions of microorganisms thriving on decaying detritus in every nook and cranny of our environment.

Composting is basically a process that utilizes the inherent abilities of these microorganisms to speed up the process of natural decay. According to the USDA (United States Department of Agriculture), this is achieved by providing an ideal environment for detritus feeding microorganisms to thrive.

If all of this sounds confusing to you, read on as we break down the science behind composting and how every household can use it to pave the way to a more sustainable future.

Why Is Composting Essential?

The United States alone generates approximately 210 million tons of trash (solid waste) each year. Most of this trash gets placed in municipal landfills. These landfills take up a huge amount of space and also release methane, one of the most potent greenhouse gases.

Furthermore, a poorly designed landfill can lead to soil pollution and toxins being released into nearby sources of groundwater. Currently, food scraps and yard waste make up more than 28% of the total 210 million tons of solid waste that Americans generate each year.

Composting is a fairly inexpensive and easy solution to reduce and utilize organic household wastes, which can be done by nearly anyone. By composting your household organic waste, you will be

  • Lowering your overall carbon footprint.
  • Reducing methane emissions from landfills.
  • Saving space in municipal landfills, which will ultimately save you tax money
  • Doing your part as a global citizen to create a more sustainable future.

Composting utilizes solid organic waste to produce humus, a rich nutrient packed substance that benefits the environment and enriches the soil as a natural fertilizer.

Not only does humus completely eliminate the need for chemical fertilizers (in most cases), it also helps moisturize the soil, suppress pests and plant pathologies, and encourage the production of beneficial bacteria.

The Biology Of Composting

How does composting work? This is something you need to understand in order to reap the aforementioned benefits of composting. Let’s look at the mechanism of composting in a little more detail.

Composting is basically a process that creates an ideal environment for the natural decay or rotting processes to take place. The key to effective composting is providing adequate conditions for detritus feeding microorganisms to thrive.

According to Cornell University, there are three main stages of composting. Each stage is predominated by different communities of microorganisms.

Stage 1: The Mesophilic Phase

The initial stage of composting involves mesophilic microorganisms (microorganisms which thrive at temperatures between 68 to 113 F). They begin breaking down soluble and readily biodegradable compounds, releasing heat as a byproduct. This stage typically lasts for a couple of days.

Stage 2: The Thermophilic Phase

The temperature rises due to the catabolic processes of mesophilic microorganisms. As the temperature rises, thermophilic microorganisms (which thrive at high temperatures) become the dominant community.

This stage may last from a few days to several months. These higher temperatures are more conducive to breaking down proteins, fats and complex carbohydrates, yielding high amounts of energy.

Temperatures tend to constantly rise during this stage. If not kept in check, the compost pile can get so hot that helpful microorganisms perish. Therefore, techniques such as aeration and turning over the compost pile are important to keep temperatures below 149 degrees Fahrenheit.

Stage 3: The Cooling Or Maturation Phase

The third stage begins to set in once the thermophilic microorganisms have used up the available supply of the high-energy yielding compounds.

This stage lasts for several months, and mesophilic microorganisms once again become prominent during this phase due to the drop in temperature. The remaining substances are broken down by mesophilic microorganisms, creating a relatively stable final product: humus from organic waste.

Other communities of useful organisms also begin to establish themselves during the maturation phase of composting.

The Useful Organisms Involved

The compost pile is actually a complex and intricate organization of billions of living organisms, working together to break down organic waste. There are two main classes of composting microorganisms namely, aerobes and anaerobes.

Aerobic bacteria require oxygen to survive and are also the most efficient at breaking down organic matter. These bacteria consume and breakdown organic waste, releasing useful compounds such as nitrogen, phosphorus and magnesium.

Anaerobes on the other hand don’t require oxygen to survive. They are not as efficient as aerobes at breaking down organic waste. Anaerobes release toxic substances and hydrogen sulfide which are not only harmful to plants but also cause composting piles to stink.

Hence, aerating the compost piles is essential to ensure that aerobic bacteria thrive and get adequate supply of oxygen.

Bacteria are the most abundant group of microorganisms contributing 80 to 90 percent of the microbial population in a compost pile. They are responsible for the majority of decomposition and heat production in a compost. Bacteria are the most nutritionally diverse group of microorganisms found in a compost pile. Along with bacteria microbial species of Fungi, Rotifers and Protozoa are also found in compost piles.

Apart from microorganisms, several other useful organisms such as pill bugs, worms and centipedes may find their way into compost piles if the conditions are favorable. These creatures break down organic waste and excrete nutrient rich substances that enrich the soil.

The Basic Requirements Of Composting

According to the United States Environmental Protection Agency, a healthy balance between “greens” and “browns” is crucial to create an ideal environment for composting to take place.

Green wastes such as grass clippings, fruit and vegetable wastes are nitrogen rich. On the other hand, brown wastes such as dried leaves, hay, wood chips and twigs have high carbon content.

According to studies, a carbon to nitrogen ratio of 30:1 is ideal for rapid composting. When considering how to build a compost pile, it is important to consider this ratio.

The Ingredients

What You Can Compost

  1. Kitchen waste, fruits, vegetables, egg shells, tea bags etc
  2. Yard and garden trimmings including grasses, leaves, twigs, house plants
  3. Other organic wastes such as paper, newspapers, cardboard, cotton and wool rags, wood chips etc.

What You Shouldn’t Compost

  1. Pet wastes, which contain harmful pathogens
  2. Diseased or infested plants
  3. Large amounts of dairy or meat products, can cause foul smell due to excess ammonia production
  4. Plants treated with chemical pesticides.

Moisture Content

The next factor to take into consideration is the moisture content of the compost pit. Adequate moisture is vital for useful microorganisms to thrive. Research has shown a moisture content of 40 to 60 percent is suitable for maintaining a healthy microbiome.


Oxygen is the next crucial element to consider. We have already seen how aerobic bacteria are much more efficient at composting as compared to anaerobic bacteria.

An oxygen deficit in your composting pile can lead to anaerobic bacteria taking over, leading to a stinky compost and toxic end-products. An easy solution to this, is to aerate your compost pile by turning over and stirring it regularly. A compost tumbler can make the process of aerating your compost much easier. A compost tumbler comes with attached handles allowing you to turn over the contents with ease.

The Entryway Drug To Zero Waste: Composting At Home

Composting can bring about several lifestyle changes in individuals. We become more aware of the waste we generate and we realize the importance of reusing, recycling and conserving. Kathy Guthowsky, the co-owner of a commercial composting company, Green Camino, described composting as “an entryway drug to zero waste”.

If you do decide to compost at home, be responsible to tend to the pile and always keep track of what you throw into it. A properly managed compost pile will not smell bad or attract pests or rodents and will produce enriching humus which you can use to nourish your garden or backyard.