top of page

Everything You Need To Know About Home Composting

Updated: Apr 11, 2018

Composting happens everywhere in Mother Nature. The irony is that human activity gets in the way of this miraculous phenomenon much more than we encourage it, and it is collectively crippling us. Composting is the harnessing and concentration of a natural process for human benefit. Its profits to society are profound, and the process is simple and free.

What is Compost?

Compost is an art, not a science. A process, not an act. It leverages biological decomposition as a critical component of the cycle of life.

Organic matter does not just melt, it is digested by tiny life forms called micro-organisms, or microbes, much in the same way the microbes live in our gut and help us digest our food.

Paint the picture in your mind, in the forest the trees don’t eat the leaves that fall, they eat what the microbes in the soil make out of them. Trees grow big and strong on the backs of tiny microbes.

We can’t see them, but microbes perform herculean tasks for many different creatures — worms use concentrations of bacteria typically found in soil in their gut to create worm castings, cows team up with anaerobic gut microbes to make manure, even termites harbor fungi in their gut to help them to digest wood.

Microbes can be found absolutely everywhere, from the glaciers of Antarctica and the seeming sterility of the desert to the insides of rocks and the depths of the ocean. And thank goodness, life would not be possible without them. They can eat just about anything including air, and even electricity.

There are two major categories of microbe — aerobic and anaerobic. Aerobic organisms operate in oxygen-based environments and anaerobic organisms without oxygen. In a compost pile or garden you want to encourage aerobic organisms, which is why typical instructions for composting call for the turning of a compost heap.

It is true that most pathogens are found in the anaerobic category, but there are many benefits to anaerobic organisms, and pathogens are mostly a sign of the food web out of balance than they are contamination. Some microbes even have the ability to not be restricted to a particular mode of life, described as having “facultative” ability.

Anaerobic microbes can also be used to cycle nutrients out of organic matter in a form of cold composting. However, in this article w will be focusing on aerobic composting methods.

In the soil the job of microbes is mostly to perform the task of breaking down organic matter into perfect plant food, or humus. Humus is a colloidal substance that is the end result of soil-based microbial decomposition.

A colloid is a substance consisting of particles that are evenly dispersed throughout another substance. Ocean water is a colloid, so is jelly, whipped cream, and muddy water. In other words, it is a super-small stable solid suspended in solution that cannot be broken down into smaller constituent parts, making it easy for plants to uptake as food in order to grow.

In Latin, humus means “Earth” and fittingly gives rise to the adjective “humble”. Humus is an unassuming substance, but very powerful indeed. Consider those trees in the forest growing from the fruits of microbial decomposition; they grow to enormous size without any fertilizer at all. Now imagine how much “plant food” is locked up in your lawn or garden?

Humus cannot be replaced by artificial fertilizers. But, fortunately for us, humus can be created through composting in the back yard if the right conditions are created and the right materials are used. This is the purpose and process of composting.

Humus is created through the teamwork of what is called the “soil food web”, an organization of integrated microbes that work together to break down death so that it can be built back up into life. A good analogy for getting comfortable with the vital importance of microbes in soil and in the composting process is to compare the soil food web with the web of life in the ocean.

The soil is essentially the ocean with air. The plankton, algae, and diatoms in the ocean are the bacteria, protozoa, and nematodes of the soil. You can even equate the coral reefs as fields of plants.

Consider the natural balance of a food web in terms of the big fish eating the little fish. Of course, there are always exceptions as the blue whale, the largest organisms on Earth, eats one of the smallest, krill. The take away is that the entire food chain survives on the smallest organisms. This is a very important insight. In the garden and in the compost pile, without a healthy soil food web you are not going to get the results that you want.

Following is a diagram of the soil food web:

Each life level in the above diagram is called a “trophic level”. Organisms than can been seen with the naked eye are called macro-organisms and those too small for us to see are the micro-organisms.

The fact that microbes are beyond our field of vision is one of the major reasons we take them for granted. During my fifteen years operating a retail gardening store it was always a surprise to discover how many people never fully realized that the soil is alive. There is another universe under our feet!

Microbes are beyond abundant. Estimates vary widely on the diversity of species, primarily because we have only sequenced ~1 × 10−22% of the total DNA on Earth, effectively zero percent. The Earth Microbiome Project aims to speed this research up but do they ever have their work cut out for them!

Estimates of microbe numbers are somewhat “back of the napkin” due to the sheer astronomical scale, but try this on for size. There are 100 million times as many bacteria in the oceans (13 × 1028) as there are stars in the known universe. Even more amazingly, dental plaque is so densely packed that a gram will contain approximately 1 × 1011 bacteria, roughly the same number of humans that are thought to have ever lived. Whoa.

The parallels of the human body in regards to how soil works are striking. By the numbers, we are barely human. According to Dr. Rob Knight of UC San Diego there are somewhere in the realm of 30 trillion human cells that make up the body, but there are estimated to be 39 trillion microbial cells. This makes us only 43% human!

On a DNA level the numbers are even more incredible. There are an estimated 20,000 genes in the human body, but conservatively above 2 million microbial genes, which makes us at best 1% human on the DNA level. When we consider the growing consensus around the importance of microbes in soil and in health, this is a rather extraordinary consideration.

Dr. Zach Bush is a leader in the research into the importance of the human microbiome to health. He has identified a wireless communication network in the human body that allows the mitochondria found inside of cells to communicate through special molecules manufactured by microbes found in our body. When the microbiome is disturbed, research is showing direct correlations to many degenerative and chronic auto-immune diseases.

In fact, in 2012 Dr. Bush took a total tact from his former allopathic approach to health when he found molecules in a soil science journal that looked like the chemotherapy he was making in the lab!

The purpose of referencing the human microbiome is to draw a parallel to the soil and highlight what little we know about things as important as human health and soil science. The compost pile is the gut of the landscape. Reverence for this can produce massive results in the garden and in the health and wellness of the human species.

When talking to people about microbes it always helps to make them real. Take a look at some microbes in action. Both are videos showing the active of microbes from a compost tea recipe viewed through a microscope:

Anytime the soil food web is discussed it is oversimplified, the soil also contains archaea, viruses, actinomycetes, algae, and more; but here is an introduction to the major trophic levels:


  • Estimated 500,000 bacteria can fit in the period of the exclamation point at the end of this sentence!

  • 1 tsp of garden soil can contain 1 billion bacteria, or the mass of two cows per acre

  • 1 tsp of compost can contain 4 billion bacteria

  • Oldest fossils known — 3.5 billion years — are bacteria

  • It is estimated there are 5 million trillion trillion bacteria on Earth. A 5 with 30 zeros!


  • Hyphae are the main mode of growth and are collectively called mycelium

  • The fruiting body of the fungi is called a mushroom, many of them we eat for dinner

  • Over 70,000 species identified, but estimated there could be over 1.5 million

  • 1 tsp of compost can contain up to 40 miles of fungal hyphae

  • Largest organism on Earth is the Honey Mushroom in OR that is 4 square miles!


  • Protozoa means “first animals”, but they are single celled organisms

  • Larger organisms called “shredders” because they eat bacteria and fungi

  • Diverse group of organisms, with more than 50,000 different types identified

  • Consist of three categories of organism — amoeba, flagellates and ciliates

  • Difficult to define protozoa due to diversity, but very important in nutrient cycling


  • Most numerous multicellular organism on Earth, over 20,000 species identified

  • Many think they are harmful, but of the 20,000 only 10 or so cause problems for plants

  • Most nematodes feed on bacteria, fungi, and other soil organisms

  • Used effectively to fight flea, grub and fire ant issues in soil

  • The largest of the microscopic organisms, some can be seen with the naked eye

Microbes are not only incredibly abundant, they do major work. The following data was generated using a very high quality compost on a residential soil sample from a property in Long Island, New York.

Sample A was the control. Sample A+ was fortified with 1 teaspoon of the high quality compost mixed with a spoon before shipment. Note the enhanced levels of each element in the A+ sample. The microbes in Sample A+ only had 1.5 days to work on the soil sample sent in the mail…imagine if they had more time?

Here is an interesting journey through the organisms found in the compost pile:

Now let’s get to the nuts and bolts of the art of making compost.

Making Compost

In composting, microbes do all of the work; but just like anything humans get their hands on, there are ways to disrupt and speed up the process.


Many are familiar with the concept of the compost pile heating up, some think this to be due to the sun, but it’s actually the activity of microbes digesting the organic matter that create the heat in a compost pile.

Some commercial composting operations use artificial heat to replicate this process, but they cheapen the process.