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Composting Basics: The Composting Process


Around the world, people have become much more concerned with their environmental impact and the idea of sustainable living as both a way to protect the planet and reduce costs in the home. As a result, home composting has gotten increasingly popular as a method to reduce waste and improve gardens without spending money on fertilizers every year. Composting is the process by which bacteria, fungi, worms, and other microorganisms break down and decompose organic waste into a stable, finished product, humus. Compost is nutrient-rich, filled with active microorganisms, and when mixed with soil can improve plant health, water retention and aeration of the soil, and can even bind to harmful heavy metals and prevent their absorption into plants. When microorganisms are provided with good materials and an ideal environment in which to break them down, compost can be obtained relatively quickly for use in the garden.

Figuring out what and how much to compost, and what constitutes a good composting environment requires a basic understanding of what happens in your compost bin to create humus. While it may just look like food and yard waste, there is a lot more going on in your compost than you can see. This decomposition happens in a few stages and requires different participants and activity to occur to catalyze each stage.

Your compost begins when you start collecting organic material for your bin. Kitchen leftovers or scraps, toilet paper tubes, and used coffee grounds and tea bags are just a few of the compostable wastes that most people toss into the garbage, and after a day of yard maintenance, you will likely have more than enough organic waste to start composting. With the use of a bin or composter, these materials can be mixed and piled together, and then the process can begin. How quickly the decomposition process starts and progresses depends on some key pieces of information: temperature, moisture, aeration, and material. Remember those microorganisms? Like most creatures, they require certain things to stay alive and active.

By adding all of that kitchen and yard waste, you have already provided them with material. To be more specific, you’ve provided them with nitrogen and carbon. Nitrogen-rich materials are commonly referred to as “greens,” including moist plant materials like grass clippings and kitchen scraps. Carbon-rich materials are called “browns,” consisting mainly of dry “brown” materials like cardboard, straw, or dead leaves. The rapidity and sweet smell of your compost will be determined partially by how you balance nitrogen-rich and carbon-rich additions to your bin. The ratio generally agreed upon by composters of carbon to nitrogen is around 30:1 (C:N, to be clear). As your microorganisms use carbon and nitrogen for energy and reproduction, your compost will begin to increase in temperature.

Heat is important to your compost because some of the bacteria that decompose waste the fastest only thrive in high heat. These microorganisms will begin to appear in your compost as the heat increases due to the activity of other bacteria consuming nitrogen and carbon. Psychrophiles, low temperature microorganisms, will start this process. As psychrophiles raise the temperature to a medium heat around 70 degrees, mesophiles will join in the decomposition, working faster and increasing the heat more. Thermophiles will begin to work on your waste when the temperature in your compost gets high, around 100 degrees. These bacteria reproduce, raise the heat, and break down waste extremely fast. Make sure that whatever method you use to compost can keep your materials insulated, as retaining this high heat will keep your microorganisms working. Thermophiles work the fastest at between 130-160 degrees, and you can use a thermometer to help you maintain the heat in your compost.

Two things you will also have to monitor in your compost are oxygen and moisture. Like us, your microorganisms need air and water to survive, and if your compost is taking a long time or doesn’t appear to be breaking down at all, a lack of oxygen or proper moisture levels could be the reason why. Aeration of your compost is critical to promote aerobic decomposition, one of two ways organic matter is reduced. Of these two ways, aerobic decomposition is the quickest, the healthiest for the environment, and causes no odor, but it requires that aerobic microorganisms have access to oxygen. Without oxygen, aerobic microorganisms will die, and decomposition will fall to anaerobic microorganisms that break down waste much slower and produce stench. Aerating your compost can be done by agitating and turning compost with an aerator, shovel, or some sort of tool, tumbling them, introducing earthworms, or providing some kind of venting on your bin or composter to allow air to flow. Your microorganisms will also want water; the ideal moisture range for compost is around 40-60%. If your compost becomes too dry, decomposition can slow significantly, and if it is too wet, lack of oxygen can also cause it to slow. A hose or sprayer can be used to add more moisture to dry compost, and covering your compost and venting excess moisture can dry wet and soggy compost. Keep a watchful eye on how much water and air is getting into your compost, and make sure your microorganisms are getting what they need.

How long the composting process takes to break down a batch of waste depends on you. If you are vigilant, keep temperatures high, aerate your compost regularly, and do all that you can to ensure that nitrogen, carbon, and moisture are balanced, the hot composting process can take less than a month. This task doesn’t need to be as labor intensive as it sounds with the help of many composters and bins on the market that have been designed to address your microorganisms’ needs and promote quick decomposition. Check out MasterGardening.com for more information about composters and compost bins, composting tools, and compost accessories to help you as you start this amazing process in your own yard.


Top left: Kessner Photography.

Bottom right: Andrew Dunn, http://www.andrewdunnphoto.com.