Peter's 12 Rules of Composting

I have been involved in the composting industry since 1989, and over the years I have developed the following twelve rules that I believe apply to nearly every situation. 

"One must think like the pile – One must BECOME the pile

- Peter Moon

Rule 1: Start with the End in Mind

With composting, it helps to have a vision of what the entire process will look like. Most of our clients use their finished compost back on their pastures or in their gardens.  Others see themselves selling their compost to cover some of their operating expenses. Still others have a dream of starting a composting business and making this their primary vocation. Whichever you choose, O2Compost can help you accomplish your goals. 

With your composting system, ask yourself what type of finished product do you want to produce? Is it your objective to better manage the organic “waste” being generated on your site or do you want to also receive outside materials such as manure from other farms, or landscaping waste or food waste to produce a blended compost product?

If you plan to use your compost on your own pastures or with field crops or landscaping, what type of equipment will you use to spread it and when? Do you have a manure spreader or will you use the bucket on your tractor? Will you stockpile your compost to spread in the spring and fall or will you take it straight out to the pastures year round?

If you plan to sell your compost, how do you plan on doing this – as a bulk product, or in bags, or both? Who are you going to sell it to, how much will you charge and what will be your method of delivery – will they drop by the farm during certain operating hours or will you take it to them in a dump trailer, or will you sell it at the local farmers market?

I strongly recommend that you start with a written plan despite thet fact that it will undoubtedly change as you gain experience with your compost system. 

One of my favorite clients in Tennessee tells a great story about how her plans changed unexpectedly. Lynn operates a therapeutic riding stable with about 20 horses. She and some of the volunteers (husbands mostly) constructed a fabulous O2Compost system and when they first started producing compost they used most of it on their own pastures. Along the way, some of their members started using the compost and the word got out to the local gardening community. Now the stable receives donations for everything that they produce, and they have a waiting list. They have gotten so many inquiries that they finally painted a sign with a green thumbs UP on one side and a red thumbs DOWN on the other to indicate whether they have compost available. All of the money that they receive goes back into the therapeutic riding program in support of people of all ages who have physical and mental handicaps.

Reference:  The Seven Habits of Highly Effective People by Stephen Covey, 1989


Rule 2: To Learn to Compost, One Must Compost 

Composting requires an understanding of several basic principles, but book-learning only goes so far. Fully understanding the art and science of composting requires hands-on experience and a considerable amount of practice.

Most people encounter four psychological stages when learning a new skill. The four stages include:

1.  Unconscious Incompetence  :  You don’t know what you don’t know
2.  Conscious Incompetence  :  You know what you don’t know
3.  Conscious Competence  :  You know what you know
4.  Unconscious Competence  :  You don’t know what you know

With regard to composting, most people have a basic understanding that it involves a natural process that converts raw organic materials into something that looks like soil. But when we use the phrase “aerated composting”, most people aren’t quite sure what we mean (Stage 1).

I explain that “aerated composting” means we are introducing airflow into the compost pile to maintain aerobic conditions throughout the pile in order to optimize the biology of the system, and that turning the pile is not required. I go on to say that the net result of this biologic process is the production of heat and that we utilize this heat to destroy pathogens, parasites and weed seeds in the mix to produce a high-quality finished product in about 60 days. Just before their eyes glaze over, they likely say to themselves, “There’s more to this than I thought” (Stage 2).

With the O2Compost Training Program, we teach people the step-by-step process to compost (let’s say) the manure and waste bedding produced by six horses, and we guide them through our training process from beginning to end. At first they may think, “What have I gotten myself into” but they dutifully monitor the composting process, make note of their observations, and ask a lot of questions. Together we refine their method of operating the system so that it works effectively and automatically with every new batch (Stage 3).

They then go on to operate their O2Compost System completely on their own and week after week, year after year, they continue to compost without giving it a second thought. At this point they seldom take pile temperatures anymore because they “just know by the way it looks and smells” that everything is working just fine. They say to their friends, “It’s really quite easy – my only regret is that I didn’t do it sooner” (Stage 4).

The First Corollary of Rule 2: “You can’t learn to ride a bicycle at a seminar”


Rule 3: Every question about composting has only one answer ... “It Depends”

Question: I am frequently asked questions like, “How big does my compost system need to be?”

There are at least two answers to this question, the “short answer” and the “long answer”. 

Short Answer: Since you have 8 horses, I recommend that you construct a 3-bin system, with each bin measuring 8-feet wide by 8-feet front to back and 4-feet high. Given that, the total footprint of the structure would be about 25-feet long and 10-feet wide.

Long Answer: “It Depends” on the number of horses that you have now and plan to have in the future. It also depends on the type of bedding that you use. If you use shavings, each bin will need to be considerably larger than if you use a wood pellet type bedding material. Also, do you want to store finished compost under the same roof? If so, we need to take that into account as well. Finally, many of our clients like to construct a multi-purpose building to store other items (feed, bedding materials, tractor implements, etc.). 

Question: Another question I hear a lot is, “How much will my compost system cost to construct?”

Short Answer: Somewhere between $5,000 and $15,000.

Long Answer: “It Depends” on the size of your system, the amount of site preparation, the configuration (top-down or on-grade), the types of materials that you use to construct it, and who does the construction: you with help from your brother-in-law, or a hired independent contractor).

“It Depends” is of course tongue in cheek, but the truth is that every answer relating to composting really does depend on many factors (e.g., climate, site topography, size of the farm equipment, etc.) and considerations (e.g., who will be doing the composting, the amount of time available, the end use for the compost, etc.). When people first learn about the basic composting principles, they want specific answers (engineers are the worst – I know because I am one). 

However, most of what we know about composting is experiential and was learned through trial and error - and there have been a lot of errors along the way (as you will see in Rule #9). As the science and art of composting developed over many years, we have learned to rely on “truths” that generally work out to be right, but not always. 

The message in all of this is three-fold. First, composters need to relax and understand that if we prepare a good mix and add oxygen, it will probably work out just fine in the end. Second, your approach to composting will evolve over time to optimize both product quality and process efficiency. And third, we learn by doing and if a batch doesn’t work out exactly as expected, it’s OK to make some changes to the mix or method and try again. That’s why O2Compost offers technical support. We want you to call us and ask, “What in the heck is going on?”


Rule 4: Oxygen is the Secret to Composting

So that we don’t have to go into a long discussion about the microbiology and biochemistry and thermodynamics of composting, I am going to ask you to trust me when I say,

”Aerobic composting optimizes the biology of the composting system, expedites the composting process, produces heat that we use to destroy pathogens, parasites and weed seeds, and results in a high-quality finished product.”

Aerobic composting means that the oxygen level in the compost pile is maintained at 10% or higher (the air we breathe at sea level contains about 20% oxygen).

Most people believe that a compost pile needs to be turned from time to time to reintroduce oxygen into the mix. This does work but only for a very short period of time. The oxygen in the freshly turned active compost pile is consumed very quickly and drops well below 10% within 30 to 45 minutes. Turning the compost pile is a lot of work for very little gain.

With an O2Compost System, an electric blower delivers air to the base of the pile every 20 to 30 minutes to replenish the oxygen in the mix. The blower is operated by a timer that is typically set to turn ON from 30 seconds to 2 minutes. What is the perfect timer setting?  (See Rule 3).

The blower cycles On and Off 24 hours a day, 7 days a week for the first 30 days of composting without having to “fire up the tractor”. It will happen even when you are on vacation. Now that’s what I call multi-tasking.

To prove this to yourself, all you need to do is: 1) fill up a compost bin with your initial mix of materials; 2) take a temperature reading to get your starting point; and then 3) turn the blower / timer ON. Within 12 to 24 hours you will see the pile temperature quickly climb 30o to 50oF. This is my absolute favorite thing about aerated composting. I will never get tired of seeing this happen.


Rule 5: Water is Life

If oxygen is the secret to composting, WATER is the magic ingredient. Aerobic microorganisms live in a thin film of water around each of the particles and this thin film serves as their “highway”, allowing populations of bacteria and fungi to grow in number and diversity and spread rapidly throughout the pile. Water also serves to reduce pile odors and helps keep pile temperatures at manageable levels.

If the compost pile is too wet (i.e., much over 65% moisture content), the pore spaces will be filled with water resulting in anaerobic conditions and the generation of offensive odors.

If the compost pile is too dry (i.e., below 50% moisture content), the microbiology of the system will crash and no composting will take place.

With the O2Compost Training Program, we offer our technical support for all of our new clients and we find that 90% of all troubleshooting relates to the moisture content of the compost mix. 

The bad news is that a “dry pile” eventually happens to everyone. The good news is that it is easy to fix simply by adding water. The bad news is that the pile will need to be broken down to rewet it. You cannot evenly rewet the mix by spraying the top of the pile. The good news is that if you ultimately have to “waste” a pile, you are much closer to getting it right the next time.


Rule 6: Composting Takes Time

Invariably, when you first start to think about composting, the phone will ring and the person on the other end of the line will try to sell you a miracle device or a secret additive that will enable you to produce finished compost in “JUST 3 DAYS”. They either don’t know what they are talking about or they are lying to you outright – probably both. You have been forewarned.

The truth is that composting is a “biologically mediated process” and it takes time. 

The initial stage of composting is referred to as the “Active Phase”. This is largely a bacterial driven process whereby the readily available forms of carbon (simple sugars, carbohydrates and proteins) are consumed, with the net result being the production of heat. The Active Phase typically takes 21 to 30 days and is generally characterized by a very rapid increase in pile temperatures followed by a gradual drop-off.

The Active Phase transitions slowly to what is called the “Curing Phase”. Curing is predominantly a fungal driven process. It is not at all unusual to see mushrooms growing out of the pile and a white filamentous material “marbled” throughout the pile. This white material is called “Actinomycetes” (pronounced: Ak-Tin-Oh-My-Seats); and it is ubiquitous in the natural environment. It is a cross between bacteria and fungi and it breaks down the more resilient forms of carbon in the mix (complex carbohydrates, hemi-cellulose, cellulose and the lignin component of woody materials).

The Curing Phase takes anywhere from 30 to 60 days and it is during this stage where the majority of textural change will take place. However, curing can also take much longer than 60 days for compost with a high proportion of wood.

Nature’s ultimate goal is to convert all organic materials to humus (pronounced: Hu-Muss), which is dark brown or black organic matter that is highly resistant to further decomposition. Producing humus from raw feedstocks can take many years.


Rule 7: There are No Decimal Points in Composting

Composting is not precise. Engineers love to calculate everything to the second or third decimal point, but with composting it’s better to round off, round up, and round often.

Example 1: When we calculate the feedstock proportions for a compost mix using a Compost Calculator (as with the spreadsheet that has been included with the O2Compost Training Program) it might tell us to mix 2.85 parts of “this” with 4.36 parts of “that” and then add 23.75 gallons of water to get a mix with a C:N of 25:1, a bulk density of 675 pounds per cubic yard and a moisture content of 62.5%. 

In reality, we would use this information as our basis to to take about 3 buckets of “this” and add it to 4 heaping buckets of “that” and hose it down until it looks good and wet. The key is for the operator to know from experience whether the mix looks good or not. This is where the art of composting comes into play.

Example 2: Virtually all composting operations measure the volume of raw feedstocks and finished product in cubic yards. A cubic yard is equal to 27 cubic feet which is equal to 204 gallons. 

A cubic yard of finished compost in the bin is about equivalent to 1.5 cubic yards in the back of a pick-up truck when it’s loaded out and equivalent to about 1.2 cubic yards when that same truck gets to its destination. This is because the compost in the bin is consolidated under its own weight, it is fluffed up in the bed of the truck and it is somewhat re-compacted due to vibration on the ride home.

Example 3: If you insert a temperature probe in a compost pile and it reads 157.5oF and you then remove the probe, reinsert it an inch or two to the right, and it could now read 152.0 oF, which temperature reading is correct?

The answer is - it doesn’t matter which is right because both are well above our goal of achieving 131oF throughout the pile for at least 3 days. When monitoring pile temperature, we are looking for trends not precision.

The First Corollary of Rule 7:  Learn to Trust the Law of Compensating Errors


Rule 8: Think BIG - Start Small

O2Compost works with a wide variety of organic “wastes” in the agricultural, municipal and institutional sectors. Many of our clients envision themselves starting a composting business (see Rule 1). For this group – and in particular for those who have never been involved with composting but see it as a golden opportunity – I always recommend that they “Think Big - Start Small”. By starting small, you can “test the water” and minimize your upfront investment and if for any reason it doesn’t work out, no harm, no foul.

First, it is important to learn the basic principle of composting and to process several batches of compost using varying mix recipes (see Rule 2).

Second, you will need to test the logistics of gathering and handling various feedstocks. If you are taking materials from other waste generators, it is important to have control over these feedstocks to avoid contaminants (non-compostable materials like plastic, metal, bailing twine, persistent herbicides, etc.). It is also very important to have control over the volumes of material that you receive. DO NOT hang a sign on your front gate that effectively says “Come One – Come All”. I did this once and it was the worst (and most expensive) business decision I ever made.

Third, have your product tested by a certified laboratory to understand the quality of your finished product. You will want to understand how your compost will affect plant growth and how it should be used. To this end, I recommend that you conduct some simple growth trials to see for yourself how it performs.

Fourth, develop a simple marketing plan. Give some of your compost away to the bellwether members of your local garden club and get their feedback. I have found this to be the fastest way to get the marketing wheel turning. When you do this, get ready for your telephone to start ringing.

Fifth, get good legal and accounting advice and develop a business plan. Most people don’t do this and ultimately experience unnecessary growing pains.

When you have done these things, scale up slowly and in planned increments. As your volumes increase, you will get to a point where you will need larger equipment and a larger working area. It goes without saying that all of this will cost you money.

Back in the early 1990’s, when I first started composting on my own, I spent a lot of time at a friend’s dairy farm where I was “playing” with sloppy dairy manure mixed with horse manure and bedding. One day my wife asked me “Is this a hobby or is this a business?”  To which I replied, “What do you need to hear?” She then asked, “Will we make any money doing this?” and I said “I think so, eventually”. She said, “OK, every man needs a hobby”. 


Rule 9: It’s Critical to Make Mistakes

(but Small Mistakes are Better than Large Ones)

The First Corollary of Rule 9: “Experience is what you get when you don’t get what you want”.

The Second Corollary of Rule 9: If it’s worth doing, it’s worth doing poorly – at first”

As I said above, “To learn to compost one must compost” (see Rule 2). Developing a good compost mix and adjusting the rate of aeration (i.e., frequency, duration and volume of airflow) is largely a trial and error process. I believe that figuring out what doesn’t work is considerably more important than figuring out what does work. 

Composting is all about working within acceptable ranges (see Rule 7), and as long as we stay within these ranges, the process tends to sort itself out in the end. Pushing the limits on these ranges (C:N, bulk density, moisture content and airflow) to the point where the composting process doesn’t work has reinforced my respect for these ranges.

The following is a quick story to emphasize this point.

I lived on five acres outside of Snohomish, Washington, a small town on the “rural fringe”. I constructed several prototype compost systems and tested them with every variety of organic waste that I can get my hands on.

Back in 2008, a friend of mine and I filled one of my Micro-Bins with a mix of about 1 cubic yard of separated dairy manure, 1 cubic yard of horse manure and 600 pounds of salmon (if you are wondering, that’s a lot of salmon). I’m guessing that the C:N of this mix was somewhere south of 10:1 (very high nitrogen). I fully expected this batch to have a strong odor so I took precautions to cover and ventilate the top of the pile and treat the off-gases in a biofilter. Unfortunately, I didn’t make the biofilter large enough and let’s just say that my backyard smelled like low tide for about a week.

During the more than 20 years that my wife and I lived on those five acres we had seen a lot of wildlife, but that week – for the first time – we saw a bear. It was the talk of the neighborhood. It’s also interesting to note that we haven’t seen a bear since. My neighbors know me pretty well and were kind enough not to complain. However, they did ask, “What do you have going on over there this time?”, which leads me to …

The Third Corollary of Rule 9: “Don’t stink up the neighborhood”


Rule 10: Every System Has Constraints

Every manufacturing process involves raw materials, facilities, equipment, trained personnel and a distribution network. Every manufacturing process also involves systems to make all of these components come together in a timely and cost effective manner. Within every manufacturing process, there are constraints – some that are quite obvious and others that are not so obvious.

Composting is a manufacturing process where organic “wastes” (our natural resource) are converted into a value added product (compost); and this rule clearly applies.

Let’s use a green waste compost facility as an example. With green waste (also referred to as yard debris) some of the materials tend to be coarse and woody and need to be reduced in size before going into the compost system. A grinder can be used for this purpose, but if the grinder is too small or it tends to break down a lot, this one piece of equipment will slow the process down and keep it from running smoothly. Unprocessed materials will accumulate upstream from the grinder, and equipment downstream will operate well below their efficient rate of processing.

If the grinder is replaced with one that works well and optimizes throughput, then some other constraint will appear – perhaps the screen that is used to refine the finished product now shows up as the bottleneck in the system. Less obvious constraints can also appear:

  • facility owners and site personnel lack proper training;
  • the types and volumes of materials being accepted at the site require operating permits;
  • a lack of good housekeeping results in odors and neighbor complaints;
  • little attention is paid to the marketing of compost products, etc.

In Rule 8, I recommend starting small and scaling up in planned increments. In the planning process, it’s important to look at all aspects of the compost system to anticipate the constraints that will inevitably show up. A flow-diagram is a great tool that will assist in this evaluation process.

The First Corollary to Rule 10: “Buy a tractor or front-end loader that is one size larger than what you think you’ll need”. 

Reference: The Goal: A Process of On-Going Improvement by Eliyahu M. Goldratt, 1992

This book is written as a novel and as a novel it’s OK, but not great. However, the message it delivers is excellent and one that should be considered by everyone who is related to a manufacturing process in any way.


Rule 11: Always Strive to Improve Product Quality

One of the primary objectives with running a compost facility is to operate it efficiently to reduce both the time and expense of processing a finished product. It is generally agreed that every compost system is unique in how it operates and that the method of operation will evolve over time. 

To this end, always striving to improve your product quality will be the key to your success. By focusing on product quality, everything else about how the compost system operates will fall into line. This is a very simple rule, but it is also a very important one.


Rule 12: Keep It Simple & Systematic (KISS)

Rule 12 is derived from Occam’s Razor, which states: “Among competing hypotheses, the one that makes the fewest assumptions should be selected”.

We all know the KISS Principle (Keep It Simple, Stupid). My version of the KISS Principle is Keep It Simple and Systematic. 

Keep It Simple: Most engineers say, “If it’s not broken, it doesn’t have enough bells and whistles”.  I believe that every compost system should be kept as simple as possible so that anyone can operate it with a minimal amount of training (and without formal training in micro-biology). This is my bias.

O2Compost systems use an electric blower that is operated by a simple cycle timer to induce airflow into the pile under positive pressure. Yes, we can incorporate a programmable logic controller that can collect and graphically display temperature data. Yes, we can operate the system using a computer that tells the blower to reverse the airflow from positive to negative aeration based on the temperature differential between the top and bottom of the pile. We can do these things, but why? It only costs more money and these features are prone to fail at the least opportune time.

Keep It Systematic: As I said above, “It is important critical to make mistakes”. Learning what doesn’t work is even more important than figuring out what does work (see Rule 9).  Composting is experiential and it is through an ongoing trial and error process that you will learn the most efficient and effective way to operate your compost system (see Rule 2). 

To take advantage of your successes (and failures), I recommend that you develop one or more checklists to follow so that critical elements don’t get overlooked. This will enable you to produce a high-quality finished product – consistently (See Rule 11).

Checklists will also help you transfer the day-to-day operations of the system to someone else so that you can use your time more productively and perhaps take an occasional well-deserved vacation.

The First Corollary of Rule 12: “That which gets measured, gets done”

Reference:  The Checklist Manifesto by Atul Gawande, 2009