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How Compost Is Made: The Definitive Guide


Compost Bin

Compost is heralded as the fix-all black gold of the horticulture world. Not only can it improve any soil type, but it is also free to make and extremely cheap to buy. It reduces waste, improves soil health, and can even give you tastier veggies from the garden.

So, what is this magic elixir, and how do we make it?

In order to understand how and where your compost will be most effective, you have to understand what compost truly is, and how it interacts with your soil.

Compost is more than the sum of its parts; it’s an ecosystem. Understanding each part of the system – and the interdependent web of life within – is the foundation for building a healthy compost pile.

How Compost Is Made: The Basics

Compost is the matured, humus-like remains of organic material that have been broken down through controlled aerobic biodegradation. (source)

So, what does that mean?

Basically, compost is the result of human intervention in the natural process of decomposition. Plant material will decompose on its own under most circumstances, but controlling the process yields the best possible product for soil improvement.

Ingredients

To build a basic compost pile, you need to start with the right ingredients.

Composting is a series of interactions between nitrogen and carbon. So, compost ingredients are measured in terms of nitrogen-heavy and carbon-heavy material.

Nitrogen-heavy (green) materials are fresh, flexible, moist plant waste.

Nitrogen-rich materials are usually fresh.

Examples of green ingredients are:

  • Grass clippings
  • Fruit peels
  • Vegetable scraps
  • Pulled weeds
  • Herbaceous prunings
  • Manure

Carbon-heavy (brown) materials are old, rigid, dry plant waste. Examples of brown ingredients are:

  • Fallen leaves
  • Hardwood prunings
  • Twigs
  • Paper
  • Cardboard
Carbon sources for composting include dried leaves, paper, and cardboard.

In general, the recommended ratio of carbon to nitrogen by volume is 2:1, with a brown layer on the top and bottom. Brown ingredients tend to be bulkier, and therefore help with the airflow.

Green ingredients are more compact and help retain moisture. Too much of either ingredient will result in a pile unable to maintain the correct balance of oxygen and water.

Mixture

Decomposition can happen in a number of environments, but the specific process needed for healthy compost is aerobic biodegradation, which means controlling the ratio of oxygen to water within the pile.

To maintain aerobic conditions, you must have oxygen. A lack of oxygen results in anaerobic conditions and this will greatly reduce the quality of your finished compost.

To maintain biodegradation, you must have water. A lack of moisture results in the death of microorganisms that break down materials into humus.

In general, the recommended ratio of air to water is 1:1, which is roughly the moisture content of a damp sponge. This ratio begins with a balance of bulky and fine ingredients but is maintained by wetting and turning the pile.

As the pile begins to break down, it loses volume. The green material will lose water content and the pile will shrink. This loss of mass helps to hold moisture in the center of the pile. Moisture allows microorganisms to move and eat, which is the majority of the decomposition process.

However, if the pile is too compact, air will not be able to move through the center, which will kill off aerobic microbes and encourage the growth of anaerobic microbes. Some anaerobic activity is necessary to break down difficult plant material, but an overabundance will kill aerobic microbes and result in a lot of useless, potentially toxic waste.

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If the pile is too loose, there will be a lack of moisture in the center, which will kill off aerobic activity and halt decomposition. Large sticks and twigs, or piles that are too small, can contribute to lack of moisture. Use a chipper to break down bulky materials into more manageable pieces.

Turn the pile about once per week to help reintroduce oxygen and pull new material into the center to be broken down. This will help avoid anaerobic conditions and will allow you to monitor moisture content. You may need to wet the pile with a hose to keep it damp.

Composting Process

Under ideal conditions, the composting process only takes a few months. A compost thermometerOpens in a new tab. will help you monitor the process to keep the pile active.

As compost breaks down, it goes through three phases. Initially, the pile heats up as decomposition begins. Once the center is hot, different microbes take over and break down the material. As it breaks down, the food source for those microbes disappears, and they die off. This is signaled by a drop in temperature, which is your sign to turn the pile.

Heat is a key component of active compost.

Folding new material into the center will introduce new food for microbes. The process begins again as the pile heats up, uses up the new material, and cools off. If the pile is turned as it cools, the time between these phases is reduced, and the compost will finish in 6-8 weeks.

Allowing more time in between phases will not harm the compost, but it will extend the amount of time needed for a finished product. Once the pile cools, it transitions from active to passive, and it must be turned and moistened to return to an active state of decomposition.

After 5-7 rotations, most of the material will be used up, and temperature fluctuations will even out. This is the sign that your compost is nearly finished, and is ready for the maturation stage.

Maturity

Compost is not truly finished until it has cured. If you turn your pile, and the internal temperature remains close to the ambient temperature, it is in the maturation stage.

Maturation is an important, but often overlooked, stage of composting. Although the temperature does not change much, many chemical processes continue to take place. These chemical reactions are transforming complex compounds into forms plants can use.

If this stage is skipped, and compost is used without curing, it will tie up nutrients in the soil to finish decomposing. This will result in a temporary decrease in nutrient availability for plants and can do more harm than good as a soil amendment.

Depending on the amount of decomposition that still needs to take place, the negative effects of using young, or hot, compost can last from a few weeks up to two years.

When is compost ready? Compost is mature when the temperature remains constant after turning, and there is no remaining recognizable organic material.

Mature compost is dark, crumbly, and has an earthy odor. Compost with remnants of leaves, vegetable scraps, twigs, or other ingredients should be turned, moistened, and allowed to continue decomposing.

Composted manure will no longer smell like manure if it is aged properly. If there is still an odor of manure, it will cause nitrogen burn if it is applied to the soil.

Finished compost can be used as a soil amendment, fertilizer, mulch, topdressing, seed starter, and container mix. Each application will require a slightly different finished product.

Seed starter may require sifting, where mulch should be bulky. A topdressing can be somewhat young, but a fertilizer should be fully matured.

Compost improves the soil on a chemical, physical, and biological level. It can be modified to improve certain soil properties, such as nutrition, pH, and structure.

Understanding the true finished nature of compost, and the processes that influence it is crucial to creating or purchasing a product that will specifically address your needs.

Now that we’ve covered the basics of the composting process, it’s time to explore the science behind the scenes.

The decomposition process of composting involves 7 key elements.

How Compost Is Made: The Details

If you’ve made your own compost before, chances are we haven’t told you anything you didn’t already know. There are tons of books, articles, and videos explaining how to build a basic compost pile, and how to use the finished product.

There’s plenty of information out there about the how of composting. Now, we’re going to explore the why behind it all.

Composting Ingredients (Organic Materials)

Compost ingredients are classified as either green or brown. Green ingredients are nitrogen-heavy, and brown ingredients are carbon-heavy. Finding the right ratio between green and brown ingredients helps compost decompose quickly and efficiently.

But, why are nitrogen and carbon the key ingredients? All living things, including “green” ingredients, are full of carbon. Nitrogen is only one of the three most crucial vitamins for plant growth. So, why do we single out nitrogen?

Nitrogen

Nitrogen is the most important vitamin for plant growth. It is the main component in chlorophyll, which is the mechanism that allows plants to transform carbon dioxide and water into sugar.  Nitrogen is also a key ingredient in amino acids.

Without nitrogen, plants would have no energy for growth, and no building blocks to grow with.

But, what is nitrogen’s role in compost?

Compost is one large digestive system. Nitrogen is one of the two main foods that are taken in, and thousands of different organisms produce enzymes to digest this food and turn it into simple compounds.

In very simple terms, compost is microbe poop. And nitrogen is microbe food.

Proteins break down into amino acids, which then break down into inorganic ions like ammonium (NH₄⁺) and nitrate (NO₃⁻). These ions are water-soluble, and can be taken up by plant roots and used to rebuild amino acids, which are then used to form proteins.

Microbes use nitrogen to grow and reproduce, and their rapid growth is responsible for the heat generated at the center of the compost pile. As microbes begin to feed on nitrogen, they multiply exponentially and consume the available nitrogen at the center of the pile where moisture is ideal.

Their activity is so voracious that they heat the pile to the point where they kill themselves off, while simultaneously eating themselves out of food. This intense heat kills off many microbes, while the rest starve for lack of nitrogen.

The pile begins to cool, and this is the signal that it needs to be turned. As new nitrogen is incorporated into the center of the pile, the microbial population begins rapid regrowth, and the process repeats.

Most nitrogen in compost is organic, meaning the majority of nitrogen is not available for immediate use. Nitrification is the process of organic nitrogen being broken down into ammonium and nitrate. This process will continue for years after the compost is incorporated into the soil, and is one of the reasons compost is an excellent fertilizer.

Mature compost only releases a small amount of available nitrogen and continues to release nitrogen at a slow, consistent rate. Many synthetic fertilizers are high in immediately-available nitrogen, which encourages rapid, unsustainable growth, and quickly leaches through the soil if it is not used.

Nitrification releases ammonia and other harmful substances. In a compost pile, this will off-gas without doing any damage. However, immature compost will release these substances into the soil, and it can cause plants to dehydrate and wither.

This is why it is especially important to allow high-nitrogen compost piles to mature completely before use. Composting piles of grass clippings or manure will take longer to cure, and may need to be incorporated into fallow ground.

Carbon

Carbon is fundamental to life. Plants are nearly half carbon, and while there is no lack of carbon for plants to use as fuel, an improper balance in a compost pile will create problems.

Microbes are 50% carbon, and they also consume carbon as their prime energy source.

Most microbes have a carbon to nitrogen ratio of about 6:1, but the demands of decomposing large amounts of organic material require a much higher carbon content.

  • If there is not enough carbon in a compost pile, microbes will feed primarily on nitrogen and break it down too quickly. This will result in large amounts of ammonia gas, which both smells terrible and lowers nitrogen content.
  • If there is too much carbon, microbes will not have enough nitrogen for rapid reproduction, and decomposition will occur at a much slower, cooler rate. Heat is a primary component for breaking down tough plant fibers, so excess carbon may result in organic material that takes years to fully decompose.

Carbon is mostly lost to the atmosphere as compost breaks down. Finished compost will have a carbon to nitrogen ratio of about 10:1, but a beginning ratio of 30:1 is needed for proper decomposition. As microbes break down plant material, 67% of carbon is released into the atmosphere as carbon dioxide, while the free nitrogen is then used as an energy source for other organisms.

Invertebrates play an important role in breaking down carbon-rich materials. Tough, fibrous plant tissue can require multiple cycles of decomposition in order to break down into fundamental elements. Food webs including slugs, snails, sowbugs, earwigs, beetles, ants, and other organisms. These organisms break down larger, tougher elements into smaller components for microbes to digest.

Particle size can have a substantial effect on the availability of carbon. Small particles, like sawdust, has a large surface area and therefore more available carbon. The same wood source could be chipped but would have far less available carbon by volume.

Mixture

Composting requires a balance of nitrogen and carbon.

Understanding C:N (The Carbon To Nitrogen Ratio)

Perhaps one of the more confusing instructions for building a compost pile is the carbon to nitrogen ratio.

Some websites will claim that a good ratio is about two parts carbon to one part nitrogen. Other sources seem to say the ideal ratio is more like 30:1. Still, others say it doesn’t matter as long as the pile smells fine and breaks down in a reasonable amount of time.

All of these claims are true. Making sense of them lies in understanding the terminology.

All plant material is much higher in carbon than nitrogen. Even green, nitrogen-rich compost ingredients are far higher in carbon than nitrogen. To say a compost ingredient is “green” is to say the carbon to nitrogen (C:N) ratio is lower than other plant materials.

For instance, vegetable waste has a C:N ratio of about 18:1 (sourceOpens in a new tab.). It is far higher in carbon content than nitrogen, but it is one of the most nitrogen-dense, “green” compost ingredients you can find.

On the other hand, wood chips can have a C:N ratio of 400:1 (sourceOpens in a new tab.), making them a “brown” compost ingredient due to large amounts of carbon and very low nitrogen content. However, all plant material will contain substantially more carbon than nitrogen.

The C:N ratio is referring to the chemical properties of plant material. The ratio of carbon content to nitrogen content needed in a compost pile is roughly 30:1 for most applications.

When sources say to use two parts brown material to one part green material, they are referring to volume, not chemistry.

Roughly speaking, you should use two parts carbon-heavy material by volume to one part nitrogen-heavy material by volume.

Each brown layer should be about 4” thick, while each green layer should be about 2” thick. However, this does not mean you will end up with a 30:1 C:N ratio by chemical makeup.

A compost pile made of grass clippings and straw will have a vastly different C:N ratio than one made of manure and wood chips, even if the layers are equal in volume.

And this is why some sources say not to worry too much about the ratio. Unless you are going to heavily research your ingredients and weigh them for an accurate C:N ratio, you’re basically guessing and hoping it works out. This is why being able to recognize an imbalance once decomposition begins is important.

Mixtures too high in carbon will be cooler and will not lose much volume.

If you have built a pile and the temperature does not fluctuate much in the first week, you may need to add material with a lower C:N ratio, like grass clippings.

Mixtures too high in nitrogen will be very hot and smell like ammonia.

If your pile loses a large amount of volume and smells like garbage, you may need to mix in material with a higher C:N ratio, like wood chips or dead leaves.

To maintain active decomposition, begin with a pile that is a 4’ cube of ingredients. This will allow the center of the pile to retain heat and moisture.

Smaller piles will have much smaller centers of decomposition and may take longer to break down.

Larger piles can decompose properly if they are built in rows, but managing them can be difficult without large equipment to turn and move them.

Oxygen

Without oxygen, piles of plant waste would be a slimy, stinky mess. Almost all living organisms that break down organic material require oxygen to live and reproduce.

As microbes break down complex organic materials, they breathe in oxygen and breathe out carbon dioxide. This helps even out the C:N ratio, and also keeps the pile in a state of aerobic biodegradation.

Active compost piles are breathing. As microbes use oxygen to break down other materials, they pull air through the pile.

Breaking down nitrogen creates heat, and as they expel carbon dioxide, the warm air pushes up through the top of the pile. This continual inhale of oxygen and exhale of carbon dioxide creates airflow through a pile with balanced particle sizes.

This continued breathing keeps oxygen coming in to fuel the microbial activity. If oxygen is unable to move into the pile, aerobic microbes suffocate and die.

Anaerobic microbes take over and begin a different decomposition process. Plant material is still broken down, but the waste material can be full of toxic substances that make the compost unusable.

However, if the pile is agitated, and oxygen is reintroduced, anaerobic microbes die off, and new aerobic microbial activity breaks down the harmful waste material.

The key to healthy respiration is a mixture of large and small particle sizes. Dense, green materials like grass clippings can mat together and restrict airflow. Bulky, brown materials can allow too much oxygen flow which causes water to evaporate and dry out the aerobic microbes.

A mixture of particle sizes will help respiration continue at an even rate, along with the consistent turning of the pile.

Anaerobic decomposition can result in acidic compost. Most finished compost product has a pH close to neutral (7). Anaerobic activity produces harmful waste in the form of acids, which lowers the pH to an almost unusable level of 4.5.

As the pile becomes more acidic, microbial activity is limited even more. This can be reversed by turning the pile, and the pH will rise with healthy, aerobic decomposition.

Water

Moisture content influences all aspects of decomposition. Many microbes live in films of water that coat the particles within a compost pile. Other microbes live in tiny air pockets between these particles. Still, other organisms tunnel through particles but die as the particles dry out.

Like C:N ratio, air to water ratio is a rough estimate. Generally speaking, the spaces between particles should be 50/50 air to water, although anything from 40/60 to 60/40 is acceptable.

Most piles, unless covered or in a protected microclimate, will dry out on the top and sides. This is normal, and does not inhibit microbial activity as long as the center of the pile can retain moisture. Many compost piles have an ecosystem in the center that is independent of the surrounding environment.

To determine healthy moisture content, pick up a handful of material from the center of the pile and squeeze it. It should be damp, but only let out a few drops of water. Too much and you risk anaerobic activity. Too little, and decomposition will slow or stop completely.

You may need to water your pile to maintain healthy moisture content. As the pile decomposes and expels warm carbon dioxide, water vapor is lost and moisture decreases.

Wetting down the pile during active decomposition will cause the temperature to drop and decomposition will halt. As long as your pile is not in a hot, windy location, it should only need supplemental water when you turn it, and this will not interfere with the composting phases.

If your compost pile is drying out quickly after turning, there may be too much carbon. Try adding some green material and checking moisture content after a few days.

The Composting Process

If a pile has been built with the proper ingredients and structure, healthy decomposition can begin.

Time

The success of a compost pile is identified by the phases it will cycle through.

The active phase of composting is a repeating cycle of mesophilic and thermophilic decomposition (sourceOpens in a new tab.). Mesophilic bacteria begin to colonize the compost pile as conditions in the center are able to support rapid growth.

Fungi, bacteria, actinomycetes, and protozoa begin to consume organic material when moisture and oxygen requirements are met. This rapid growth is signaled by a spike in the internal temperature, which consequently kills off the mesophilic organisms.

As the mesophilic phase ends, the thermophilic phase takes over. Thermophilic organisms multiply exponentially, creating an intense heat that can kill pathogens and weed seeds. This heat can also break down tough plant fibers and phytotoxic compounds.

As thermophilic organisms run out of organic material to consume, they die off and the mesophilic microorganisms reemerge. The pile cools, and this is the signal to mix or turn the compost. This will add new plant material to the center of the pile, and the cycle will repeat.

During the active phase, the internal temperature will fluctuate between 60º and 160º. When the temperature drops to 100º, it is time to turn the pile. The temperature will drop, then climb, then fall back to 100º as the mesophilic and thermophilic phases cycle through.

If you turn the pile and the temperature remains constant, the pile has moved from the active phase to the curing phase.  The curing process is a steady decline in mesophilic decomposition, followed by a few months of sitting and maturing.

This maturation phase is often overlooked, but it is the difference between a helpful amendment and an organic herbicide. Immature compost can release organic acids into the soil, contain large amounts of salt, or severely lower pH.

As compost matures, chemical compounds are broken down into final forms that are able to be used by plants. Harmful gasses are safely expelled, salts can leach out, and pH will stabilize.

Under ideal conditions, compost can be ready to use in only three months. Home compost piles may take as long as two years, however, if the active phase is not consistently maintained.

Maturity

As stated above, if all the requirements are met for healthy biodegradation, compost will be ready to use after a few months.

Mature, cured compost can be used for a number of applications. The benefits of compost are a direct result of the structure and composition of the finished product.

Humus

The term humus is contradictory in soil studies. In fact, many in the field claim humus does not even exist.

Traditionally, humus is identified as the skeleton of decomposed organic material. Mature compost will continue to break down once it is incorporated into the soil. In a few short years, the bulk of compost is almost completely broken down and reabsorbed by plant roots.

However, a small percentage of decomposed material will remain as a stable fixture in the soil. It will resist future decomposition and will retain its structure. It is negatively charged, which helps it hold on to ions that would otherwise be lost through leaching. It also helps the porosity of the soil by retaining water while allowing excess moisture to drain freely.

This material has been referred to in the past as humus, and it is a major benefit to adding compost to your soil.

Unfortunately, humus is not a term that is well understood, accepted, or regulated. Humus (if it exists) makes up only 2-3% of the bulk of compost, and it is nearly impossible to separate out into a solo product.

This does not stop manufacturers from labeling their compost as “humus”, and charging more for their products. There is no quick fix for adding large amounts of humus to your soil, and it may be harmful even if it were possible.

The only way to build up the humus content of the soil is to add cured compost on a consistent basis.

Nutrient Profile

As organic material decomposes, complex compounds are broken down into fundamental elements. These elements are able to be utilized by plants, which then build them back into complex structures.

Most of these fundamental compounds are the vitamins and minerals that plants need in order to grow and reproduce. The composting process breaks down these nutrients into plant-available forms, which is why it is often used as an organic fertilizer.

There is no way to know the nutrient profile of your compost without ordering a compost analysis from a lab. However, there is a generally-accepted range that most healthy compost products should fall within that can give you an idea of what you are putting back into your soil.

[Infographic] - Compost Nutrients Breakdown

Regardless of the quantity of nutrients in compost, they will only be available if the pH is close to neutral. If pH is too acidic or basic, nutrients can become chemically tied up and unable to be used by plant roots.

Some compost ingredients can intentionally alter the pH, like pine needles and coffee grounds. However, these ingredients would have to be in high quantities to make much of a difference. Plus, altering the pH of a pile can throw off the entire decomposition process and produce a low-quality product.

It is better to create a healthy, balanced compost pile for your lawn and garden, and then use other amendments to correct pH levels. Adding gypsum or lime to your soil gives you much more control over final pH levels than trying to manipulate the pH of a compost pile.

Mature compost acts as a mild, slow-release fertilizer for many years. Most of the nitrogen and other nutrients are still bound in unusable forms even once the compost has cured. Once the compost is incorporated into your soil, it will continue to slowly break down and release those elements over time.

The nutritional benefits of one compost application can last over a decade depending on the plants that are growing in the soil.

The key to nutritional benefits from compost is consistent applications. One application can help some, but yearly applications will build upon themselves and add a substantial amount of slow-release nutrition.

This gradual release of nutrients can also harm soil depending on the original soil profile. The ability to hold onto nutrients is helpful for nitrogen and other nutrients that can easily leach out of the soil. However, nutrients like phosphorus will bind with the soil particles and build up over continued compost applications.

Phosphorus is necessary for root growth, but in high quantities it becomes toxic. Excess phosphorus can prevent nitrogen from being absorbed by plants, and can tie up other nutrients in the soil. Because phosphorus is so difficult to remove from the soil, it is important to continue yearly soil tests to monitor nutrient levels.

Phosphorus buildup is evidenced by stunted plant growth and an overall decline in health. A soil test can confirm toxicity.

You can remove phosphorus with expensive chemical treatments, but a more reasonable option for most gardeners is to cease compost and fertilizer treatments and plant a cover crop of nitrogen-fixing plants like peas. These can bring nitrogen into the soil while using phosphorus to grow, which can help even out the nutrient profile.

Monitor nutrient levels annually, and experiment with a variety of compost ingredients. Manure is generally responsible for high phosphorus content, so try using other nitrogen-rich ingredients like grass clippings.

Uses

Compost has a wide range of uses depending on your growing needs. The general properties of compost as a fertilizer is what makes it so versatile.

Compost can retain nutrients and make them available on a slow, consistent basis. This makes them an ideal soil amendment or fertilizer. For bare soil, mix in a ¼”-½” layer of compost into the topsoil before planting.

For vegetable gardens, spread a layer on top of an empty bed, and gently rake it in. Tilling each year will destroy the structural benefits of organic matter and create unhealthy soil conditions in your garden beds.

Compost will improve the structure of any soil. It will add porosity and help drainage in clay soils, and it will add bulk and help water retention in sandy soils.

For established lawns and landscapes, apply compost as a topdressing to build up a healthy topsoil layer.

Lawns need about ¼” of compost spread on top and watered in. Trees and shrubs can take a much heavier layer of 1”-2” out to the drip line, and this will act as a topdressing and mulch.

With a little preparation, compost makes a cheap seed starter and soil-mix ingredient. Sift compost by placing a compost screen over a bucket or wheelbarrow.

The screen should be fine enough to catch small rocks and grubs, but large enough to allow some bulk to fall through. Window screens are too fine for compost.

Sifting cured compost will result in a uniform, aerated mixture that will hold up well as a seed starter or in a raised bed mixture.

Compost: Enhancements

Knowing the why behind composting helps in understanding the basic process.

However, knowing the rules is only half the equation for making high-quality compost. Once you learn the rules, you can bend them, and customize your compost for your particular needs.

Bins

Many compost piles are just fine as a free pile on the ground, but there are a number of reasons to build a compost bin.

There are a number of advantages to building a compost bin:

  • Conserving space
  • Aesthetics
  • Organization
  • Easy-access for machinery and tools
  • Deterring wildlife
  • Promoting decomposition with small piles
  • Speeding up decomposition
  • Worm composting
  • Improving aeration

Compost piles can spread out and make a mess, especially when you turn them. Building a bin can help contain your pile and make it easier to aerate, mix, and move.

Simple containment bins can be four corner posts with some chicken wire or wood scraps for sides. Leave one side open for easy access.

A four-sided compost bin with a gate can be used for a more aesthetic compost bin. Use non-treated wood or fencing, and put a gate on one side for access. Aeration is important for compost bins, so make sure the sides are able to allow airflow.

Chicken wire or chain-link fencing can help deter some wildlife from your pile, although using the proper ingredients is a far better solution.

Generally speaking, the only reason wildlife will be attracted to your compost pile is if you are using ingredients that don’t belong. Meat, cooked food, bones, and other foods may decompose over time, but they are not suitable for a compost pile.

For composting in small spaces, you may need a micro-bin or Opens in a new tab.micro-tumbler (like this oneOpens in a new tab. on Amazon) to aid decomposition and help retain heat and moisture.

Ideally, compost piles should start as a 4’ cubic pile. But, compost can be made in spaces as small as a soda bottle (sourceOpens in a new tab.). If you’re tight on space, or low on ingredients, try buying or building a micro-bin, and use small amounts of compost in potted plants.

Some climates may require compost bins in order to maintain temperature and moisture. Extremely hot, cold, windy, dry, or wet climates may not allow the compost to break down successfully. Covering a pile can help retain moisture, or keep out excess water, but it can also prevent aeration.

Try building a simple compost bin and use a tarp to cover the bin, while leaving space above the pile. Insert pipes into the pile for aeration, and take care to turn or mix it to prevent anaerobic conditions from forming.

Another option for extreme climates is a compost tumbler. This makes your compost pile mobile, which can help for small-scale use. One tumbler can make enough compost for a small vegetable garden or flower bed.

Click here Opens in a new tab.to browse and check the latest pricing on manufactured compost tumblers at Amazon.

Composting With Worms

Compost can be made using worms, also known as vermicomposting.

If you want a high-nutrient content fertilizer, consider building or purchasing a worm binOpens in a new tab.. Red wiggler worms will break down organic material into nutrient-dense castings, which can be used in small quantities in specific applications.

Worms need a brown material for bedding, like shredded newspaper or cardboard, and they are fed green material as they grow. If it is maintained properly, a worm bin does not smell and can be stored under the sink or in a garage for easy access.

And yes, you can absolutely compost those Amazon boxes. Click here to read more.

Worm bins, or vermicomposting, follow different rules than a typical compost pile. It is technically a form of composting, but all of the chemical processes happen within the digestive system of the worm.

The bin should not heat up or fluctuate in temperature, and there is no need to turn the material because the worms create tunnels for aeration as they eat.

Composting Ingredients

Compost can be slightly altered depending on the types of ingredients, and the ratio of carbon to nitrogen.

The nutrient content is most easily manipulated by the addition of manure. Horse, cow, and chicken manures have high nitrogen content and few pathogens that can affect humans.

Composting manure can yield a product higher in nitrogen and phosphorus, and is more potent as fertilizer than composted grass clippings or vegetable scraps. However, unless you are planting heavy feeders on a consistent basis, composted manure can cause phosphorus toxicity if it is applied annually.

Altering the pH content can be a little more difficult, but it is possible if you have the right ingredients.

Pine needles, coffee grounds, and oak leaves will lower the pH of compost until it has fully decomposed.

It can also cause unfavorable conditions for some microorganisms, and therefore a pile with lower pH can be harder to maintain. The effects on pH will last until the organic material has fully decomposed, which can take a few years once it is incorporated into the soil.

Compost Amendments And Accelerators

There are many advertised products that are supposed to accelerate, manipulate, and activate your compost pile. Most are completely useless and downright harmful to the composting process.

The terms used for compost amendments are largely unregulated and poorly defined. Good compost is a product of a natural process that takes time. Accelerating or manipulating it chemically is not necessary and can inhibit the microbial activity that is working hard to give you a good product.

There are only two situations where a compost amendment is helpful.

Soil

Microbes live on everything, and your compost will be full of them. Many migrate up from the soil and into the organic material as they begin to break it down.

If you are building compost piles on slabs of concrete, asphalt, or other foundations that do not have access to soil, you may want to throw a few handfuls of soil in with your ingredients. It is likely unnecessary, but it can help get the process started, and it’s free.

Nitrogen

If you are composting lots of brown material, you may need a nitrogen amendment to maintain healthy decomposition within the pile.

Large piles of leaves, twigs, and paper need nitrogen for the chemical process of biodegradation, but you may not have access to the necessary quantities of green material.

You can buy urea, blood meal, and other nitrogen-heavy amendments to make up for the lack of green ingredients, but you will need much less by volume than a traditional layer of weeds or veggie scraps.

You will lose the benefits of water and heat retention that wet, dense, nitrogen-heavy organic material provides, but these amendments will at least help the decomposition process begin, and it will speed up the decomposition of tougher materials.

While it is possible to manipulate certain properties of compost, it is always better to allow the process to happen naturally and in its own time. Amendments, different styles of bins, and altering ingredients should only be done in response to problems, and not in an effort to make compost do a job it was not intended to do.

There are a vast amount of soil amendments and conditioners that are specifically formulated to influence certain soil properties, and they give you much more control over the desired outcome.

If you are adamant about using a compost accelerator, click here to read our top recommended brands.

Conclusion

Compost is a complex, dynamic ecosystem that provides many long-term sustainable benefits for soil. Once you have an understanding of the why behind the how, you can recognize unhealthy situations and how to correct them.

It is also easier to recognize which soil issues compost can help fix, and which it may potentially aggravate.

Even if you don’t make your own, understanding how compost is made can help make purchasing decisions for certain applications.

It will also help you determine whether or not a certain product has been composted correctly, and may create issues in your soil.

However, most importantly, compost is as much an art as it is a science. We’ve explained the scientific details to aid understanding, but once you get a feel for healthy compost, you may find that bending or breaking a few rules gives you better results.

Are you building a compost pile?

Check out our other articles for information on how to build an active compost pile, common compost problems, and which foods should never make it into your compost bin.

Sydney Bosque

Sydney has over 15 years of experience in lawn maintenance, landscape design, and organic gardening. She has an A.A.S. in Landscape Design/Organic Produce Production from the Nebraska College of Technical Agriculture.

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