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.
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. They are oxidizing the organic matter and creating mulch, not humus.
Temperatures can reach up to 140 F in a compost pile, and this is a good thing. High temperatures kill pathogens and weed seeds that may make their way into the pile.
The process may slow in cold weather, but it never stops. The best way to determine if your compost pile is cycling properly is to feel it. If it is producing heat the microbes are active. When it starts to cool the process is coming to completion.
It is a common conception that it is necessary to turn compost. The reason for this is because you want to encourage aerobic (with air) process, as opposed to anaerobic (without air) process.
However, it is not necessary to turn compost. Actually, the less you turn it the better it becomes. Again, composting happens everywhere, one does not need to turn the forest floor, right?
Turning compost can help to mix ingredients if they are added over time, but is normally a compensation for a lack of biological diversity. Meaning, if the microbes are not present to do the work the human has to step in. This can also be to an imbalance in the C:N ratio of the inputs, which we will discuss below.
Biodynamic compost is typically made up all at one time and either buried or left in static piles to decompose over time, and is some of the best compost in the world. To learn more about biodynamics look into the Biodynamic Association, Demeter USA, or the Josephine Porter Institute.
It is possible to turn your compost too much. Don’t turn compost any more than two times a week. Any more disrupts the heat that builds up and prevents the process of biological decomposition from occurring.
So it will speed the process up to turn the pile, but good things come to those who wait!
If you are balancing your compost and adding fresh and aged material in proper balance then moisture should not be an issue. This is especially true if your pile is exposed to the weather. A proper pile will retain all of the moisture it needs from the fresh inputs and rain.
Generally, below 40% moisture biological activity slows and above 60% moisture aeration is hindered and drowns the microbes, but a biologically balanced pile will drain to a perfect moisture level every time.
There is no need to water compost. It should feel like a wrung out sponge when you squeeze it.
The size of the particle in your compost pile can affect the length of time it takes to decompose. The smaller the size, the more surface area and the quicker the biological digestion can occur.
So it is not absolutely necessary, but if you can use a paper shredder and be mindful to grind up the material you put in your bin it will break down much faster.
The Carbon to Nitrogen ratio (C:N) is the only part of home composting you have to think about. The closer you balance your inputs the more success you will have.
Keep in mind that this is not an exact science, don’t measure the volume of your inputs, it is more of a feel. Nevertheless it is an important part of the process.
The ratio of the elements themselves should be around 30:1. This translates to around a 2–3:1 ratio by volume of material. Microbes use C for energy and N for reproduction. So an imbalance of one to the other prevents the microbes the materials they need to be successful.
Generally speaking, carbon-based material is brown and nitrogen-based material is green. There are always exceptions, coffee grounds are brown but high in nitrogen.
Think of a fresh pile of grass. It’s green when you cut it and after a matter of days it turns brown as it ages. The nitrogen in the grass is lost to the air, as almost 80% of the air is nitrogen.
This highlights the benefits of mulch mowing your lawn. It turns out you can accomplish around 3–4 nitrogen fertilizer applications a year simply by leaving your clippings on your lawn to break down. Of course, you need a healthy soil food web in order to prevent it from turning into thatch!
Carbon = “Browns”
High C:N ratio = above 30:1
Generally dry and slow to decompose
Used as energy source for microbes
Ex: straw, dry leaves, wood chips, paper
Nitrogen = “Greens”
Low C:N ratio = below 30:1
High moisture, fast to decompose
N is raw element of proteins used to build microbe bodies and for microbial reproduction and digestion
Ex: veggie scraps, fresh grass, green leaves, manure, coffee grounds
Anything that was once alive will compost, but there are some things that are better than others if your intention is to use it in the garden. Generally, avoid artificial materials and cooked or refined substances.
The following is by no means a complete list, and you will find some disagreement on some of the items listed, but this is assuming it is a healthy compost pile.
Weeds are fine to compost, but for those who are wary consider steeping weeds in a drum of water for 4–6 weeks to ferment and then return the liquid to the landscape. Weeds grow due to deficiencies in the soil, so this is a good way to add back what Nature is trying to generate.
Here are some DO’s and DONT’s of composting ingredients:
DO Compost = raw food waste, lawn clippings, chopped leaves, shredded branches, garden plants, shredded paper, weeds, straw or hay, newspaper, wood ash (small volumes), coffee grounds, etc.
DON’T Compost = meats, cheeses, oils, cooked foods, bones, cooked rice, large sticks, excessive wood ash, pine needles, heavily coated paper, treated wood, or anything you feel is artificial.
If you follow the general guidelines above you will have great success composting. Once you get comfortable with the process it will become second nature.
Here is a handy troubleshooting guide to the most common composting issues:
Too much nitrogen → add aged brown high carbon material
Compaction → turn or aerate
Overwatering → add dry material and turn
Pile Not Heating Up
Lack of nitrogen → add fresh green high nitrogen material
Low moisture → add water and feel for heat
Heap not large enough → ensure it is at least 3x3'
Compost is finished → use it
Much of the work done by people in tending their compost pile is due to a lack of the proper microbes to do the work. Intentionally adding microbes to a compost heap is called “inoculating”.
Inoculation can be accomplished by accessing quality soil from the garden, but often times growers use artificial materials and biocides and do not having living soil. In this case it help to source some soil from a natural undisturbed source such as field or the forest. You can also purchase natural inoculants often sold as “compost tea inoculants”.
Think of it like a “mother” for baking bread or making vinegar. The microbes perpetuate given proper conditions, and assuming you are not coming in behind them using artificial fertilizers, pesticides and herbicides, will perpetuate to extraordinary populations.
It is important that a proper compost inoculant come from Nature, not from a lab. Many “compost starters” on the market come with only a selective group of microbes that do not represent adequate diversity to be successful. While they are certainly beneficial on some level, they are extremely limited relative to the potential of the entire soil food web.
Soil does seem to be characterized by a redundancy of functions. Research does not show a relationship to exist between microbial diversity and decomposition of organic matter. However, there is no qualitative analysis done to determine the value of the humus created.
Think of it this way, imagine if humans tried to turn a freshwater lake into the abundance and diversity of the ocean? There is no possible way a human can choose the proper microbes that should be found in a compost pile.
Benefits of Compost
The benefits of compost are almost never ending, and both direct and indirect. Up to 50% of the average home’s waste stream can be composted. Not to mention the benefits of living soil in recycling toxins, sequestering water, benefits to crop growth, and on and on.
Here is a decent list:
Increases organic matter in soil
Helps plants grow
Balances clay or sandy soil
Buffers soil pH
Moderates soil temperatures
Helps control soil erosion
Increases air quality
Lowers landfill waste
Reduces greenhouse gases
Composting is fun!
Buying compost is risky business. The reason is that most of the time commercial compost is a stable form of recycled industrial waste of some sort. Very little attention is put on the diversity of the microbes accomplishing the decomposition.
In other words, compost is an easy word to say or print on a bag.
If you are buying compost from a Big Box store you can pretty much assume it has no immediate value, and it very well may harm your crop. It is more than likely aged and stabilized manure, and gut microbes are not soil microbes. Meaning, just because the manure was allowed to off-gas and is no longer “hot”, does not mean that soil microbes have been given an opportunity to do their work. Proper composting is ALL about the soil microbe.
It is interesting to note that worm castings require no further composting. This is because they live in the soil and the microbes that they harbor in their gut are soil microbes. Compare this to animal manure that have anaerobic guts and retain completely different profiles of microbes.
If you are buying your compost in bulk, ask your provider what attention they pay to soil microbes and inoculating their piles. Ask them if they have a microbe test on file. If they do, all trophic levels should be present. If not, then you can pretty much assume they have no idea what you are talking about. In this case, do not pay more than $50 for a cubic yard for the material.
As long as the organic matter you purchase is clean it can be worked with by purchasing a good compost tea inoculant, brew up some compost tea, and break it down yourself. You can also get some mother material from a friend with successful compost and even go access some soil from the forest floor where the microbes have not been disturbed. The more diversity the better, there is strength in diversity.
This can be done before or after you add it to the garden, but ideally before so that the microbes have some time to get to work converting the organic matter to valuable material.
A common question people ask is, how do you know when it is ready to use?
Compost is ready to use when it is dark, brown, and crumbly with an earthy odor. There are respiration tests you can buy to monitor the process, but once you perform the process a couple of times and see the results it becomes second nature.
Crumbly compost should be fluffy, not moldy or rotten, and it does not need to be decomposed to a point of being powdery. The original materials that went into the compost pile should no longer be recognizable in finished compost, except maybe for some woody pieces if they have been used.
The temperature of the finished compost should be the same as the outside air temperature, and the material should not reheat. If it is not a contained bin you will see earthworms and other insects now that the temperature is lower. If it is an enclosed compost bin consider adding some worms for extra benefit.
If your compost is still hot, smells like ammonia, or you can still recognize much of the original material which went into the pile, then it is not ready to use yet. Once the compost appears finished, many let it sit for a couple of weeks to make sure the decomposition process has stabilized.
One of the main reasons to compost everything before you put it into the garden is that bacteria digesting the organic material that is not completely broken down may compete with plants for nitrogen in the soil in order to perform the decomposition process. Plants will look stunted and yellow, and unfinished compost has been found to also retard germination and growth of seedlings. However, if your soil is alive this is not too large of a consideration.
Specific uses for compost:
Mulch: Compost can be used just like mulch, but with many added benefits. Spread it around in a 2–3 inch layer to plants, trees, shrubs — the usual players in your garden or lawn. Because it is already broken down you will need to add it more frequently than regular wood chip mulch, maybe 1–2 times a season, but you will have the healthiest landscape on the block!
Soil Amendment: When using compost as a soil amendment, mix liberally into the soil or potting mix. A good raio is 10–20% of the overall volume of soil the plant is using. Because it is very difficult to overuse compost unless plants are planted directly into 100% compost, the more the merrier.
Compost Tea: Compost tea is a great way to step your composting game up big time. Composting is concentrating soil, well compost tea is concentrating compost. This is ideally done through the aeration of water and the introduction of microbe food sources like molasses, fish, kelp, etc. In the presence of oxygen and food the microbes grow to extraordinary concentrations. Read The Ultimate Guide to Brewing Compost
Tea for more ideas.
Lawn Top Dressing: A top dressing is applying compost on top of the soil. The lawn is a good place to bring your compost if you have an abundance of material.
Apply anywhere from 1 to 3 inches of compost to the lawn and rake and water it in. Although it might look like you have a pile of dirt on your lawn for the first week or two, it will eventually settle into the soil and disappear, leaving you with much healthier soil that requires less fertilizer, holds more water, and keeps your grass nice and green.
Tips For Making Better Compost
Be Patient: This is counter intuitive to many who have researched composting, but the best compost comes from heaps not turned. This is not to say that turning compost harms the heap, it will speed the process of composting up through providing more air to the microbes operating in the pile. However, there is a value in challenging the soil microbes. Allowing microbes to operate in a “facultative” (operating in both aerobic and anaerobic capacities depending on conditions) nature found in some species of microbes makes them stronger. no different than children not spoiled are more capable. Consider that the forest floor is never turned! This only works when the C:N ratio is ideal and the heap is properly inoculated. If you do turn your heap don’t do it more than once per week.
Buy a Compost Bin: Don’t take this is a strong suggestion given the suggestions above, but buying a compost bin is required for some growers that have an HOA, animals they want to keep out of the heap, or dogs that may make a mess of things. It is absolutely not necessary to have a compost bin to enjoy the benefits of composting, but they can be convenient for speeding the process up if that is the intention of the grower.
Have Multiple Heaps: For growers that want to use compost aggressively, it can help to have multiple heaps. This allows to stop adding organic material to the original pile and add to a second heap in order to finish the first. It is not a hug deal to add uncomposted material to a gardening application, but it is considered ideal to finish the composting process before adding material. This multiple heap set up will allow the grower to be more aggressive using the compost with the least trouble separating from uncomposted material.
Add Worms: If you have a compost bin adding worms makes a great addition, as they add a new level of value to the soil food web. This is only really beneficial if the bin is enclosed and worms cannot make it in from outside. If you have an open heap that is connected to the soil you will find that worms find the heap on their own. Worms are not eating the organic matter, but the microbes that are eating the organic matter, like the big fish eating the smaller fish. Many purchase worms to add to the garden when the garden is not alive with microbes, resulting in them moving away seeking more fertile environments. In the garden ,use worms as an indicator, when you see them you know you are on the right track!
So there you have it, everything you need to know about composting. If I missed something, kindly let me know.
Remember, people do not make compost, microbes do. Composting is more of an art than a science, don’t hold on too tight. The microbes self-organize, they know exactly what to do, your job is to present them with a loose range of organic materials so they can do their job and get out of the way!
Now go get started and then teach your friends, the world needs it!