As gardening takes more and more of a foothold in the lives of homeowners, many are exploring the benefits of taking their home and yard waste and turning it into compost, a highly beneficial soil amendment
Through natural biological processes composting takes unwanted waste and breaks it down into organic matter particles full of nutrients and beneficial microorganisms
This guide explains the benefits of composting, the science behind it, the different ways it can be done, and how to effectively compost for yourself.
In This Article
What is Compost?
To define it simply, composting is the biological process that takes home and garden waste — food scraps, grass clippings, leaves, etc. — and allows microbes to break the materials down into a rich soil amendment called compost. Decomposition occurs naturally, albeit, slowly over time; composting is the act of speeding up this process by providing ideal conditions needed for microorganisms to thrive.
The resulting product is amazingly rich in organic matter, nutrients, and beneficial microbes. The “black gold” created is used extensively in gardening but also in landscaping, and both commercial horticulture and agriculture applications. Any system where plants are grown in soil benefits from the addition of compost.
Benefits of Composting
The benefits of turning waste into compost and then applying it to the soil isn’t a secret. A quick internet search or a conversation with a composting aficionado provides plenty of information but the gains run far deeper for both your soil and the environment.
Compost helps to improve soil structure and drainage when added to garden soils, flowerbeds, and agricultural fields
Using compost as a soil amendment also aids in environmental sustainability by reducing erosion and nutrient leaching, and lessening the application of water as well as synthetic, chemical inputs such as fertilizers and pesticides
When it comes to composting, most people are aware of the following soil benefits:
- Improved soil structure. Adding organic matter results in lighter and more friable soil; preventing heavy clumps that are hard to break apart. Roots freely move through the soil profile, spreading out easily for improved water and nutrient uptake.
- Increased soil nutrient concentration and availability. Well rotted, or “finished” compost is a plentiful source of nitrogen, potassium, phosphorus, and other nutrients essential for plant growth. Over time these nutrients are slowly released from the compost and made available for plant uptake. Compost also has an ionic charge that holds onto these nutrients and others that are in the soil from fertilizers sources, keeping them in the root zone for plant comsuption.
- Improved water holding capacity and drainage. In light soils, compost absorbs moisture, keeping more water in the root zone. This keeps soil from drying out quickly. In heavy soils that don’t drain well, adding compost improves the soil structure. Excess water moves through the root zone instead of saturating the soil.
- Adjusted and buffered soil pH. The organic material in compost attracts both negatively and positively charged ions in the soil; in both acidic and alkaline soils this ion attraction brings the soil closer to a neutral pH and buffers pH changes over time.
The environmental benefits aren’t as well known as the benefits of using compost as a soil amendment, but it doesn’t mean they aren’t as important
Composting has advantages that contribute substantially to environmental sustainability.
- Reduced nutrient leaching out of the soil. Nutrients are held to the compost particles through ionic attraction, reducing leaching through the soil profile and possible contamination of water sources.
- Reduced waste in landfills and resulting greenhouse gas emissions. Food waste put into landfills breaks down slowly, producing methane gas during decomposition; composting waste at home reduces the overall contribution to landfills and methane emissions into the atmosphere.
- Less water consumption. An important benefit of adding compost to soils is how it increases water holding capacity. A soil that doesn’t dry out as quickly doesn’t require watering/irrigation as often, reducing overall water consumption.
- Decreased fertilizer use. Compost slowly releases plant essential nutrients into the soil and helps hold nutrients in the root zone. This reduces the need for fertilizer applications.
Science Behind Composting
At the most basic level, composting is the breakdown of yard and kitchen waste by microorganisms naturally found in the air, water, and soil. The breakdown of materials happens in 3 different stages and is driven primarily by two different classes of organisms.
The Stages of Composting
In the first stage, mesophilic organisms begin to physically break down the materials into smaller pieces. Mesophiles grow best in moderate temperatures between 68 and 113℉. This stage takes a couple of days and corresponds with increasing temperatures within the pile.
The second stage occurs when the temperature within a composting system is too warm for mesophilic organisms. At this point, thermophilic microorganisms take over
In the final stage, the thermophilic microorganisms use up the available supply of materials and the temperature of the pile begins to drop, allowing the mesophiles to resume control of the process again. They continue breaking down the organic materials into the usable, finished compost.
Microorganisms at Work
Within the different stages of composting, two types of bacteria are primarily at work: aerobic bacteria that need at least 5% oxygen to
Aerobic bacteria are the more efficient of the two and complete most of the work. They release nutrients such as nitrogen, phosphorus, and magnesium.
The anaerobes are less efficient and can release hydrogen sulfide, creating an undesirable smell.
These two types of bacteria make up 80 to 90% of the microorganisms in compost piles; the remaining percentage of microbes in compost is made up of fungi, including yeast and molds.
Carbon vs. Nitrogen
Most decomposable materials are carbon or nitrogen-based to varying degrees (for simplicity sake).
In order for microorganisms to decompose these materials, a compost pile needs to have the correct ratio of carbon to nitrogen to provide a balanced diet for the microbes.
Carbon-based materials provide energy for the microorganisms and give compost its light, fluffy nature. These “brown materials” consist of items that are more wood-based, or fibrous: dried leaves, branches, stems, sawdust, tree bark, corn stalks, pine needles.
A simple rule of thumb is to make sure your compost pile has approximately 2/3 “brown” (i.e. carbon-based) materials and 1/3 “green” (nitrogen based) materials
Brown materials add bulk to the pile without adding weight. This encourages air circulation, allowing oxygen to penetrate the inner area of the pile. If there is more green material than the microorganisms can consume, the excess nitrogen is released as ammonia gas.
Hot vs Cold Composting
There are two different tenants of composting: hot composting and cold composting
Hot composting is the more active of the two processes
The conditions are carefully maintained to keep the process working efficiently. Ingredients are combined in a preferred 2 parts carbon to 1 part nitrogen ratio
Cold composting is a passive, more laid-back process
Ingredients are piled together as they are available and let to naturally breakdown with little intervention.
A cold composting pile doesn’t reach the same internal temperature a hot composting pile does; due to this, it takes much longer — 1 to 2 years — to get a finished, usable product.
Different Types of Composters
One of the great things about composting is the flexibility it offers in regards to the different types of setups available
Open bins consist of a partial structure that allows for ventilation and aeration while keeping materials confined to a specific area
One side is easily accessible to add new materials and turn the pile as needed. Common systems have a single bin or a 3-part system where there is a bin for fresh materials waiting to be composted, a bin actively in the middle of hot composting, and a bin where the compost is allowed to finish
Pros: great for hot composting, easy to construct, keeps materials tidy and somewhat hidden, can hold a large amount of compost.
Cons: construction costs add up quickly depending on the materials used, 3 bin systems need a larger amount of space.
Enclosed compost bins offer homeowners with limited space an easy option for composting.
The composting bins are typically made from thick, recycled plastic and come in a variety of different sizes and shapes. The process is completely enclosed via a lid and eliminates both the sight of a compost pile and the smell.
On the downside though, the size of enclosed bins limits the
Pros: materials are kept out of sight, a minimal smell is given off, and the system is very neat and tidy.
Cons: cost, limited amount of space to work with, hard to harvest finished compost.
Tumblers are a unique — and the most efficient — type of enclosed compost bin
They are typically cylindrical in nature, almost drum-like, and have a handle that allows them to be “turned” or tumbled easily. This circumvents the need to stir the compost periodically with a shovel or pitchfork to provide aeration and mixing of ingredients
Pros: very easy to “stir” materials, keeps composting material completely out of sight, smells are minimized.
Cons: cost, limited space, not as easy to access finished compost.
Pit composting is just as the name implies: a pit or trench is dug and materials are thrown into it with little effort exerted
Pros: no money spent on materials, decomposing material is out of sight, no maintenance or effort needed.
Cons: takes a long time for finished compost, requires the manual labor of digging a pit or trench.
Piling works well for those interested in either hot or cold composting and don’t have space constraints or worry about camouflaging the smell
Pros: no cost, no need to build anything, easy to turn materials, easy to harvest compost.
Cons: compost pile is not concealed, the smell can be noticeable.
Worm bins (also known as vermicomposting) are a great option for apartment dwellers or people who have limited outdoor space as they work inside the home
Pros: great for small spaces, works year round, can be done indoors
Steps to Composting
If you choose to compost, the process entails more than throwing yard and table scraps into a heap
- Clear a space in your yard or garden with tiller or cultivator, exposing the bare soil. This allows earthworms and microorganisms to come up out of the soil into the compost pile, driving decomposition.
- Build a layer of straw or twigs. A couple of inches of material helps to aerate the pile and provides good drainage.
- Add layers of materials to be composted, alternating between wet and dry layers. Wet layers consist of food scraps, tea bags, etc. Dry layers can be straw, dried leaves, sawdust pellets, etc.
- Incorporate a nitrogen source. Manure or grass clippings work well and help activate the pile.
- Keep the pile moist. Water it occasionally, or let natural rainfall do its job.
- Cover your compost pile. You can use plastic sheeting or plywood to cover the top of the pile. This helps retain moisture while protecting it from the extra rainfall that would make it too wet.
- Turn the compost pile every couple of weeks with a shovel or pitchfork, or spin the tumbler if you are hot composting. This aerates the materials, providing oxygen to the aerobic bacteria involved in the decomposition and distributes fresh materials within the pile.
Maintaining a Compost Pile
If you choose to have a hot compost pile, it’s important to optimize the temperature, oxygen content, and moisture level within the pile to make the process efficient.
When conditions are sub-part composting slows and may stop completely.
Composting occurs when the ambient temperatures are above freezing
The process runs quicker the warmer the temperature of both the air surrounding the pile and the material within the pile
The internal temperature of the compost pile is the best way to know if the materials are breaking down
The bacteria primarily responsible for breaking down the materials need oxygen to work, making it important to supply oxygen to the entire compost pile.
It’s generally recommended to stir or tumble the pile every two weeks
There needs to be adequate moisture in the pile without being waterlogged. Microbes, like all other organisms, need water to survive. Too little and they die; too much water and they suffocate from lack of oxygen.
Ideally, your compost pile should have a moisture content of 50-60%. Experienced gardeners recommend the moisture in a pile be similar to that of a wrung-out sponge
Tips on Composting
No matter the type of composting system you choose to implement, the following tips are helpful.
- Think of your compost pile as a pet; it needs regular attention if you are hot composting.
- Build your own composting bin if you can’t find one you like.
- Put your composter in a dry, shady spot in close proximity to a water source.
- Add a variety of kitchen and yard waste.
- Follow a 2:1 brown to green ratio.
- Chop yard and garden materials into smaller pieces using a lawn mower or simple pruners/shears if feasible.
- Alternate a brown layer with a green layer to minimize odors and insects.
- Keep the pile moist but not saturated.
- Maintain the appropriate temperature within the pile.
- Turn the pile frequently to add oxygen and stimulate the microbes.
- Add in natural fibers from clothing, wine corks, coffee filters, and tea bags.
- Supplement an open pile with worms.
- Expect a small amount of odor as decomposition proceeds.
- Don’t add food waste (fish, meat, dairy products, bones, fatty foods or grease) since they do not break down easily. This slows the timeframe down and invites rodents and other small critters.
- Don’t let food waste accumulate at the top of the pile where it can attract vermin. Mix it in well.
- Don’t put worms in an enclosed bin or tumbler; they work best in a pile or pit where they easily move back into the soil underneath.
- Don’t include plant roots in the pile. Their nature is to take hold and if allowed to grow, it makes turning the pile incredibly difficult.
- Don’t add diseased plant tissue or weeds to the compost pile to reduce the risk of contaminating your compost. The internal temperature may be adequate for composting but not high enough to kill diseases or weed seeds.
- Don’t add pet feces or used litter.
- DON’T MAKE COMPOSTING HARDER THAN IT HAS TO BE! It is a natural process that shouldn’t cause you stress. Roll with the punches and figure out what works for you.
Knowing When Compost is Ready
When your compost has completed the decomposition process and is ready to use it will look, feel, and smell like really, dark, crumbly soil
The pile will have shrunk significantly – to approximately one-half of its beginning size – and none of the original materials will be recognizable
At this point, it is ready to be removed from your composter and used in your garden
Composting is increasingly becoming a do-it-yourself project for many gardeners because of its soil and environmental benefits
Knowing the science behind composting, and understanding the biological process helps you determine what system is best for you personally while minimizing problems you may have. The information included in this guide on composting will easily have you well on your way to creating your own black gold!
Do you plan on starting a compost pile or already have one going? I’d love to hear your thoughts below.