Glossary of Composting Terminology

Whether you’re just getting started in composting or have extensive experience, some of the scientific terminology may be unfamiliar to you. On this page you’ll find many of those terms defined.

ACTINOMYCETE — A group of microorganisms that usually produce a characteristic branched mycelium. These organisms are responsible for the earthy smell of compost.

AERATE, AERATION — To aerate compost or soil is to introduce air into the compost or soil.

AERATED STATIC PILE — A compost pile that is not turned (static), but is aerated through ventilation pipes that run through the pile. These may be PVC pipes with holes drilled into them.

AEROBIC — Containing air, containing oxygen, occurring in the presence of oxygen.

AEROBIC DECOMPOSITION — The oxidation of organic matter into carbon dioxide and water by microorganisms in the presence of air.

AEROBIC RESPIRATION — A form of respiration whereby microorganisms consume oxygen and produce carbon dioxide and water and release energy for their life processes.

AGGREGATION — A mass or body of individual units or particles. Healthy soil has good aggregation. As microorganisms and worms feed, they form polysaccharides which act like glue to hold individual soil particles together, creating groups, or aggregates, of particles. This loose formation allows soil to hold both water and air, and does not restrict the growth of roots.

ALKALINE — A basic reaction in which the pH reading is above 7.0.

ALLELOPATHY — The repression or destruction of plants from the effect of certain toxic chemical substance produced and released by other nearby plants, particularly from the roots.

ALLELOPATHIC — As above with adjective tense.

AMINO ACIDS — Complex acidic compounds containing a molecule of ammonia (NH3). Large numbers of these linked together form the protein molecule.

AMMONIA — A colorless, pungent gas, NH³; A form of nitrogen that has 1 part of nitrogen attached to 3 parts of Hydrogen NH3.

AMMONIUM — Present in salts produced by the reaction of ammonia with an acid: A form of nitrogen that has 1 part of nitrogen attached to 4 parts of Hydrogen NH4.

ANAEROBIC — Lacking air, lacking oxygen.

ANAEROBIC RESPIRATION — A form of respiration in the absence of oxygen whereby organisms convert organic matter into methane gas, alcohols, or other organic compounds and carbon dioxide.

ASH — The white or grayish powder remaining after material has been combusted at 500°C plus or minus 50° in the presence of excess air.

AVAILABLE — In general, a form capable of being assimilated by a growing plant.

BACTERIA — Microorganisms that break down organic materials in the first stages of composting. It is bacteria that generate the heat associated with hot composting. The three types of bacteria are psychrophilic, mesophyllic, and thermophilic.

BALANCE — Soils function best as a growing media when physical, biological, and chemical factors are all within desirable ranges. Soil within these ranges are referred to as balanced.

BASE SATURATION PERCENTAGE — The percentage of the soil exchange sites (CEC) occupied by 5 Basic Cations, such as potassium (K), calcium (Ca), magnesium (Mg), hydrogen (H), and sodium (Na). The base saturation percentages are calculated for each cation, and then added up to determine base saturation.

BIODEGRADABLE — Complex compounds that can be broken into simpler chemical compounds by microorganisms or larger particles into smaller particles. Organic materials are biodegradable.

BIODIVERSITY — In a natural environment undisturbed from outside influences, there is a variety of plant and animal life, ranging from the very small to the very large. Nature has created a natural system for pest and disease control. However, when we only utilize a limited variety in our landscapes, the system of checks and balances breaks down. In general, the more diverse we can make our gardens, the healthier they will be.

BIOLOGICAL — With microorganisms or micro life – A substance containing micro life.

BIOLOGICAL LIFE — A state of living microorganisms.

BIO-REMEDIATION — Conversion of toxic substances to non-toxic substances by micro life.

BOD — Biological Oxygen Demand; the amount of oxygen used in the biochemical oxidation of organic matter. Or organic matter that consumes oxygen in the process of breaking down either directly or indirectly by the microorganisms that consume oxygen as they eat the organic matter.

BIOSOLIDS — Digested septage and sewage sludge; secondary sludge.

BRIX — The level of complex sugars and nutrients in a growing plant.

BROWNS — The term “browns” is used to denote organic materials high in carbon, more specifically, materials whose carbon to nitrogen ratio is higher than 30:1. (Materials high in nitrogen are referred to as “greens”). Achieving a carbon-to-nitrogen ratio of about 30:1 is one factor in creating favorable conditions for backyard pile composting.

BUFFERING — The capacity of a compost product to work well with soils of various pH ranges. Or the capacity of any substance functioning well in a wide range of pH.

BUGS — Usually MBS uses the term to refer to the microorganisms active in compost or soil, but occasionally it is used in reference to insects.

BULKING AGENT — Material added to a compost system to maintain airflow by reducing compaction.

CARBON-TO-NITROGEN RATIO (C:N) — The relative amount of carbon to nitrogen, e.g., a 2:1 ratio means that there is twice as much carbon as nitrogen. Bacteria, like all living organisms, require quite a bit of carbon and comparatively less nitrogen. By providing them with materials that provide these elements in the correct proportion, they thrive, grow, and multiply. Therefore, they can decompose your compost pile at their highest speed. Achieving a carbon-to-nitrogen ratio of about 30:1 is one factor in creating favorable conditions for backyard pile composting.

CASTINGS — Manure, i.e., excretion, of earthworms. Earthworm castings are high in nutrients for plants and microorganisms.

CATION EXCHANGE CAPACITY (CEC) — A measure of the amount of negative charge in the soil. In the other words consisting of the total amount of the Base Saturation 5 Cations.

CFU/gdw — Colony forming units per gram of dry weight.

CHEMICAL — In science, chemicals are elementary substances such as oxygen, hydrogen, nitrogen, etc. In the context of home composting, however, the word “chemical” is often used to describe a philosophy considered to be in opposition to the organic philosophy. In general, the chemical philosophy encourages people to force nature to do what they want by applying synthetic pesticides and fertilizers which may get the temporary results they want, but may harm or not enhance the general soil condition and environment.

CLAY SOILS — Soils with clay particles and small air pores. Water retention is high creating poor drainage conditions.

COMPACTION (OF SOIL) — Compaction of soil is a lack of air or oxygen. Particles of soil are pressed together so tightly that there is insufficient air space. The obvious way this may occur is when a great weight is present, i.e., during construction when large trucks are daily rolled over the land. However, chemical overuse and poor irrigation are more common causes. In healthy soil, natural processes provide aeration, notably the presence of earthworms burrowing their way through the soil.

COMPOST — Completely decayed organic matter. It is dark, odorless, and rich in soil benefits.

COMPOST COVERS— Sometimes called Compost Fabric. A nonwoven geotextile material made from polypropylene that sheds water yet is able to exchange air through it.

COMPOST TEA — Water in which finished compost has been steeped to cultivate a liquid fertilizer for plants.

COVER CROP — A small grain crop, such as oats, wheat, or barley, not grown for harvest.

DECAY — To rot, break down, or decompose.

DECOMPOSE, DECOMPOSITION — Decay. Rot. The breaking down of organic materials into smaller particles until the original material is no longer recognizable.

DIVERSITY — It means the same thing as a large variety. How many different kinds of microorganisms are present in a sample.

EARTHWORM CASTINGS — Manure, i.e., excretion, of earthworms. Earthworm castings are high in nutrients for plants and microorganisms.

ENUMERATION — The numbers of microbes present in a sample.

ENZYME — Complex proteins produced by living cells to catalyze specific biochemical reactions.

EXCHANGE CAPACITY — A measure of a nutrient-holding power of a soil or soil amendment, such as compost. Cation exchange capacity concerns positively charged ions. Anion exchange capacity refers to negatively charged ions.

EXUDATES — Root excretions which work symbiotically with microbes to form an ideal microbial environment.

FABRIC COVERS — In composting, specially designed covers applied to windrows to manage moisture levels, protect from UV rays, while simultaneously permitting gaseous exchange.

FEEDSTOCK — Biologically decomposable organic material used for the production of compost; the materials to be decomposed through the composting process.

FLEECE — See Compost Covers and Fabric Covers.

FLOCCULATION — The process by which small particles of fine soils and sediments aggregate into larger lumps. Results in a more air space in the soil.

FOLIAR — Pertaining to leaves.

FRESH COMPOST — Organic matter that has gone through the thermophilic stage of composting and achieved pathogen kill, but is only partially decomposed and has not yet stabilized.

FRIABLE — Easily crumbled. Healthy soil is friable, so if you hold up a handful of soil and wiggle your fingers the particles of soil should fall out of your hand.

FULVIC ACID — A constituent of humus, fulvic acids are amino acids that emerge from a process of decomposition of organic matter. They operate enzymatically within seed tissue to increase water absorption, respiration, and speed germination; they also enhance root initiation and act as a growth hormone to increase secondary and lateral root development.

FUNGUS — A group of simple organisms that lack a photosynthetic pigment

GREENS — The term “greens” is used to denote organic materials high in nitrogen, more specifically, materials whose carbon to nitrogen ratio is lower than 30:1. (Materials high in carbon are referred to as “browns”). Achieving a carbon-to-nitrogen ratio of about 30:1 is one factor in creating favorable conditions for backyard pile composting.

GYPSUM — The common name for calcium sulfate, a mineral used as a source of calcium & sulfur.

HARDPAN — A hardened or cemented soil horizon or layer.

HEAVY METALS — Trace elements whose concentrations are regulated because of the potential toxicity to humans, animals, or plants. (Includes copper, nickel, cadmium, lead, mercury, & zinc if present in excessive amounts).

HERBICIDES — Agents used to inhibit plant growth or kill specific plant types.

HOT COMPOSTING, HOT PILE — Optimum conditions for compost piles, including 30:1 Carbon-to-Nitrogen ratio, 1” or smaller particles of various sizes and textures, moisture, air, minimum windrow depth of 3 cubit feet, produce an environment that will encourage and create an environment for psychrophilic, mesophyllic, and thermophilic bacteria. As the thermophilic bacteria work, the compost pile will reach high temperatures.

HUMUS — Decomposed organic matter. Healthy soil will consist of about 3.5 to 5% of this organic matter. Humus is soft, sweet-smelling, shapeless dark and crumbly and smells like the forest floor (more correctly, the forest floor smells like humus because that is what is naturally there). It is this stage of the decomposition process which provides nutrients for plant life. It contains about 30% each of lignin, protein, and complex sulfurs. It contains 3 – 5% nitrogen and 55 – 60% carbon. Humus is the slow-release food source for plants & microorganism development. It is constantly being transformed into acids, enzymes and minerals and, therefore, must be constantly replenished for proper vegetative nutrition. Note: In the final formation stage of humus being formed the extraordinary substance that really impact plant growth is Fulvic Acid, Humic acid, and Humin Acid.

HUMIC ACID — The main constituent of humus, composed of proteins and partially degraded lignin’s. They are amino acids that emerge from a process of decomposition of organic matter. They operate enzymatically within seed tissue to increase water absorption, respiration, and speed germination; they also enhance root initiation and act as a growth hormone to increase secondary and lateral root development.

HUMIFICATION — The process of making humus.

HUMIN OR HUMIN ACID — An organic acid derived from humus, being formed mostly in the final stage of humus formation.

HYDROGEN — A flammable, colorless, odorless, gaseous, chemical element, the lightest of all known substances.

INOCULANTS — Dominant microorganisms which may be added to a compost pile. Generally, these are not necessary as there are microorganisms living on all organic matter, so your pile already has these in it.

INORGANIC — Substance in which carbon-to-carbon bonds are absent; mineral matter.

LANDFILL — Pleasant term for a garbage dump which is located in a cavity in the ground so that, when full, it may be covered up and look like part of the land. Today’s landfills are sanitary and require special technology to eliminate methane gas and toxic leachate produced by the garbage.

LEACHATE — Liquid “run-off” (result of :LEACHING). Leachate from the compost pile contains nutrients generated in the composting process. In contrast, as groundwater and rain flow through a landfill, they pick up weak acids created by decaying organic matter. As these acids react with other garbage, the leachate can become toxic which may contaminate streams and groundwater unless the landfill is properly constructed to contain the run-off.

LEVERAGING NATURE — To increase or multiply the vigor or benefit of already existing forces in nature to our advantage.

LIME — Lime is sometimes added to compost piles to increase pH. However, unless you are seeking a high-pH compost it is unlikely you need to add lime. Compost piles become acidic in the initial stages as organic acids are formed. However, as the composting process continues, the pH returns to a balanced state. If you add lime, an odor may occur because of the formation of ammonia gas.

MACRONUTRIENTS — Nutrients that plants require in substantial doses. They include nitrogen, phosphorus, potassium, calcium, sulfur and magnesium.

MACROORGANISM — Living organisms in the soil which are large enough to be seen with the naked eye. Includes mite, millipede centipede, snail, slug, spider, ant, beetle, cut worm, earthworm, rodent.

MATURITY — The degree to which a biomass sample is free of organic phytotoxic substances.

MESOPHILIC BACTERIA — This group of bacteria species work to break down organic matter under “warm” conditions of 40 degrees up to 110 degrees. The ideal temperature of their environment is 70 to 90 degrees.

METHANE GAS — Explosive (when highly concentrated) gas that is formed when organic materials decompose in anaerobic conditions which exist in landfills. Landfill operators must have a method of venting methane gas before it becomes volatile.

MICROBE — (See microorganism)

MICROLIFE — Life which can only be seen with the use of a microscope. Microorganisms.

MICRONUTRIENTS — Nutrients that plants require in small doses, primarily to enhance the ability to absorb macronutrients. They include iron, manganese, copper, boron, molybdenum,chlorine, cobalt and zinc.

MICROORGANISM (MICROBE)— These are microscopic plants and animals. They exist in soil for the purpose of breaking down organic matter into basic mineral elements. (See mineralization) They include bacteria, fungi, actinomycetes, algae, protozoa, yeast, germs, ground pearls, and nematodes.

MINERALS — Supply food and nutrients for plants and microorganisms. Webster defines minerals as “any naturally occurring substance that is neither vegetable nor animal”. In other words, these are the most basic form into which organic matter can be broken. At the mineral stage, the particles are inorganic.

MINERALIZATION — Organic matter is broken down into humus, then acids, enzymes and compounds, and finally into basic mineral elements in an inorganic form.

MRF — Material recovery facility.

MSW — Municipal solid waste.

MULCH — Covering for soil. Mulch should not generally be mixed into the soil, it is not a fertilizer or soil amendment. There are many types of mulch, including partially decomposed compost, bark, wood chips, hay, nut shells, pine needles, and others. The point is to cover bare ground so that top soil is not washed away, soil temperature is buffered, and weeds are reduced from lack of light. A good organic mulch will also supply nutrients to the earth as it decomposes.

MUSHROOM COMPOST — Cellulose-rich organic matter that has undergone the initial biological decomposition stage; used by mushroom growers.

NITRATE — A form of nitrogen that has 1 part of nitrogen attached to 3 parts of oxygen N03.

NITRITE — A form of nitrogen that 1 part of nitrogen attached to 2 parts of oxygen N02.

NITROGEN DRAFT — Incorporating high-carbon matter like wood chips into the soil (i.e., mixed into soil, not placed on top) can cause deficiencies in the amount of nitrogen available to plant roots. Organic matter composts and, in order to compost, the high-carbon material requires the nitrogen from the soil to create the desired diet for microbial action.

N-P-K — N-P-K is an abbreviation for nitrogen (N), phosphorus (P), and potassium (K). In the chemical philosophy, these three elements are considered important to force crop production (as opposed to the organic philosophy goal of improving the biodiversity of the soil). U.S. law requires that the ratio of these three elements be specified on every bag of commercially-available fertilizer. A ratio of 3-1-2 or 4-1-2 is considered good.

ORGANIC — A substance that contains carbon-to-carbon bonds. Literally refers to something derived from plant or animal matter. Includes anything that is or was living, made from something living, excreted from something living. The term “organic” is used to describe a philosophy of working within the laws and systems existing in nature to achieve a healthy environment that is bountiful long-term. Healthy soil is the foundation of this philosophy; therefore, the term comes up frequently in discussions of home composting.

OXYGEN — A colorless, odorless, tasteless, gaseous, chemical element that occurs free in the atmosphere, forming one fifth of its volume, and in combination in water, sandstone limestone, etc. : it is very active, combines with nearly all other elements, is the most common element in the earth’s crust, and is essential to life processes and to combustion.

PATHOGEN — An organism or microorganism capable of producing an infection or disease in a susceptible host.

PERLITE — Volcanic mineral used as an amendment in potting soil.

PFRP — Process to further reduce pathogens.

pH — For our purposes, pH is a scale from 1 to 14 which expresses the relative acidity or alkalinity of the water in soil. A pH of 7 is neutral, i.e., neither more alkaline or more acidic. Values below 7 are acidic, increasingly acidic toward 1. Values above 7 are alkaline, increasingly alkaline as the values increase toward 14. pH is the standard abbreviation for “potential hydrogen” which denotes the hydrogen ion concentration of a solution.

PHOTOSYNTHESIS — The process by which green plants combine water and carbon dioxide to form carbohydrates under the action of light. Chlorophyll is required for the conversion of light energy into chemical energy.

PHYTOAVAILABLE — Available to vegetation.

PHYTOTOXIC — Toxic to plants. Partially composted organic matter may have acids or alcohols present that will harm young or sensitive plants. Partially-decomposed compost is therefore referred to as phytotoxic.

PLANT RESIDUE — After a plant’s yield has been harvested, that remaining portion of the plant which is ready to decompose in the soil.

POROSITY — The fraction of soil or compost volume not occupied by soil or compost particles; a measure of the pore space of a material or pile of materials.

PSYCHROPHILIC BACTERIA — This group of bacteria species work to break down organic matter under “cold” conditions of 0 degrees up to over 55 degrees. They generate low levels of heat.

REDOX — {red(uction-)ox(idation) } Chem. OXIDATION-REDUCTION — As it relates to Compost and soil, it simply indicates whether or not each individual mineral particle has Oxygen or Hydrogen attached to it.

REDUCTION, SOURCE REDUCTION, REDUCE — Practices which result in the reduction of wastes without additional energy expended for recycling, composting, disposal, etc. Examples are: minimal packaging, lowering demand for disposable products, leaving grass clippings and leaves on the lawn, and learning to read/write/review data online without printing it onto paper.

RHIZOSPHERE — Soil that surrounds and is influenced by the roots of a plant.

SALTS — The products, other than water, of the reaction of an acid with a base. Salts commonly found in soils break up into cations and anions when dissolved in water.

SANDY SOILS — Low total quantity of pore space even though individual pores are large. Water retention is low.

SANITIZED COMPOST — Compost which has gone through a pathogen reduction cycle so that disease producing organisms in the finished compost are below the level of a health risk.

SCREENING — The sifting of compost through a screen to remove large particles and improve consistency and quality of the end product.

SHARPS — Items such as needles and pins which might contaminate a waste stream.

SHREDDER — Powered mechanical devise used to break waste materials into smaller pieces.

SOIL AMENDMENT — Matter than, when added to the land, will make the soil healthier by such means as balancing and adding nutrients, balancing the pH, and encouraging the presence of microorganisms. From a legal standpoint, this is different than “fertilizer” and is not governed by the laws which regulate fertilizers.

SOIL STRUCTURE — The combination or arrangement of primary soil particles into secondary particles, units, or peds. resulting in a porous soil that allows air and water to freely move through the soil.

SOLID WASTE — Garbage, refuse, and other discarded solid material.

SOLUBLE SALTS — Soluble salts concentration is the concentration of soluble ions in a solution, measured by electrical conductivity; conductivity varies by the number and type of ions contained in the solution; each end user group of compost products will have its own salinity standards for growing specific plants or crops. Too high salts can result in phytotoxicity.

SOURCE SEPARATION — In homes or commercial operations, waste is separated into categories for recycling, composting, or landfilling. This is a fancy name for separating your newspapers, glass, yard wastes, plastic bottles, etc. into separate containers or piles for waste processing.

STRUCTURE RATING — An estimate of the density, weight, and porosity of a compost feedstock.

SULFATES — The products of sulfur combining with oxygen.

SULFIDES — The products of sulfur combining with hydrogen. In composting it represents the presence of an anaerobic environment.

SUSTAINABLE AGRICULTURE — An agricultural system which both produces crops profitably while progressively renewing or improving the soil’s fertility from year to year.

STABILITY — The level of biological activity in a moist, warm, and aerated biomass sample. Finished compost will have low levels of activity, consuming little nitrogen or oxygen and generating almost no carbon dioxide or heat.

SYNCHRONIZATION — Feedstock’s decomposing with and against each other at similar rates of speed.

TEA — See Compost Tea

THERMOPHILIC BACTERIA — This group of bacteria species work to break down organic matter under “hot” conditions of 104 degrees up to 170 degrees. This type of bacteria can perform the greatest decomposition in the shortest amount of time.

TILTH — Tilth describes soil that is well flocculated and structured, meaning that there are many pore spaces where air and water can reside. It is land which has been prepared for growing crops by plowing and fertilization. In discussions of composting and organic gardening, the phrase “the tilth of the soil” is often used to describe the general health of the soil including a balance of nutrients, water, and air.

TIPPING FEES — Fees received for accepting waste material from another source.

UREA — The commercial synthetic acid amide of carbonic acid containing not less than 45% nitrogen. It can fast start the nitrogen side of a compost windrow, but quickly disappears.

VERMICOMPOSTING, VERMICULTURE — Using red worms to compost food scraps, newspapers, and cardboard, yielding nutrient-rich castings.

WINDROW SYSTEM — Rather than making a square or round compost pile, some people make a long row. This is especially true of commercial operations. The compost pile is about as tall as it is wide, but may be as long as space allows. This row of compost is called a windrow.