Glossary of Composting Terms
Every term you need to know, explained simply.
About This Glossary
Composting has its own language. Whether you are reading about carbon-to-nitrogen ratios, thermophilic bacteria, or the difference between a brown and a green, this glossary gives you clear, plain-English definitions for every term used across our composting checklists. Bookmark it and refer back whenever a word puzzles you.
Aerobic
Decomposition that occurs in the presence of oxygen. Healthy composting is an aerobic process — it requires air to function properly and produces a pleasant, earthy smell rather than foul odors.
Bokashi
A Japanese method of composting that ferments food waste in an airtight bucket using inoculated bran (EM-1). Unlike traditional composting, bokashi can handle meat, dairy, and cooked foods without attracting pests.
Bokashi Bran
A mixture of bran (such as wheat or rice) inoculated with effective microorganisms (EM-1). It is sprinkled between layers of food waste in a bokashi bucket to initiate the fermentation process.
Bokashi Tea
The liquid that drains from the bottom of a bokashi bucket. It is rich in organic acids and beneficial microbes. Dilute it 1:100 with water before applying to garden soil as a soil drench.
Brown
Carbon-rich dry materials such as shredded cardboard, dried leaves, straw, and paper. Browns provide energy for decomposers and must be balanced with greens to maintain a healthy compost pile.
Carbon-to-Nitrogen Ratio (C:N)
The balance between carbon-rich browns and nitrogen-rich greens in a compost pile. An ideal ratio is approximately 25:1 to 30:1, which translates roughly to three parts browns for every one part greens by volume.
Castings (Worm Castings)
The dark, crumbly, nutrient-rich waste produced by worms after digesting organic matter. Worm castings are one of the most valuable soil amendments available, packed with beneficial microbes and plant-available nutrients.
Decomposition
The natural process by which organic matter is broken down into simpler substances by bacteria, fungi, and other microorganisms. Composting accelerates decomposition under controlled conditions.
Earthworm
A worm that lives in soil and burrows deep underground. Do not use garden earthworms for composting — they prefer deep, undisturbed soil and will escape a bin environment.
EM-1 (Effective Microorganisms)
A proprietary blend of beneficial microorganisms including lactic acid bacteria, yeast, and photosynthetic bacteria. EM-1 is the active ingredient in bokashi bran that ferments food waste anaerobically.
Food Waste
All organic kitchen scraps including fruit and vegetable peels, coffee grounds, tea bags, eggshells, and leftover cooked food. Food waste is the primary nitrogen-rich input for most composting systems.
Green
Nitrogen-rich materials such as food scraps, grass clippings, coffee grounds, and fresh plant trimmings. Greens provide the protein that decomposers need to multiply and break down organic matter.
Hot Composting
An active composting method that builds a large pile (at least 3x3x3 feet) and manages carbon-to-nitrogen ratios, moisture, and turning to reach temperatures above 130°F (54°C). This kills weed seeds and pathogens while breaking down waste in weeks rather than months.
Lasagna Bed (Lasagna Composting)
A no-dig gardening method that builds a raised garden bed by layering carbon-rich browns and nitrogen-rich greens directly on the ground. Each layer is soaked with water, and over time the materials decompose into rich soil.
Methane
A potent greenhouse gas produced when organic matter decomposes without oxygen (anaerobically). When food waste sits in a landfill, it generates methane. Composting with proper airflow prevents methane production by keeping the process aerobic.
Moisture (in Composting)
The amount of water content in a compost pile. Ideal moisture is approximately 70–80%, often described as the feel of a wrung-out sponge. Too much moisture causes anaerobic conditions and odors; too little slows decomposition.
Nitrogen (in Composting)
An essential nutrient that decomposers need to build proteins and reproduce. Nitrogen-rich materials are called greens and include food scraps, grass clippings, and coffee grounds. Too much nitrogen causes foul odors; too little slows decomposition.
Organic Waste
Any biodegradable waste derived from living organisms, including food scraps, yard trimmings, paper products, and plant matter. Organic waste makes up roughly 30 percent of landfill material.
Red Wiggler (Eisenia fetida)
The most common species of worm used in vermicomposting. Red wigglers thrive in compost bins, eat approximately half their body weight per day, and produce nutrient-rich castings. They are not the same as garden earthworms.
Sheet Mulching
Another name for lasagna composting. It involves smothering grass or weeds with cardboard and then layering organic materials on top to build fertile soil without tilling or digging.
Thermophilic
Heat-loving microorganisms that drive the hot composting process. Thermophilic bacteria raise pile temperatures to 130–160°F (54–71°C), which rapidly breaks down organic matter and kills weed seeds, pathogens, and grass seeds.
Vermicomposting
The process of using worms — primarily red wigglers — to decompose organic waste into nutrient-rich castings. Vermicomposting can be done indoors or outdoors in a compact bin and is ideal for apartment dwellers, urban gardeners, and classrooms.
Worm Bin (Vermicomposting Bin)
A container designed to house a worm composting system. Common options include 10-gallon plastic totes with air holes, breathable fabric bags like the Urban Worm Bag or Vermibag, and commercial stacked-tray systems.