Composting Glossary


Sproutsactivator Activators are additives to the compost pile which contain a nitrogen source or sugars. Their purpose is to increase microbial activity. Generally, adequate nitrogen organic waste is the only activator needed. If you have insufficient nitrogen, a substance like cottonseed meal may be added to encourage decomposition.

aerated Static Pile Composting system that uses a series of perforated pipes as an air distribution system running under the compost pile and connected to a blower. The pile is not turned.

aeration Bringing about the contact of the compost with air through turning, or ventilating to allow microbial aerobic metabolism.

aerobic Occurring in the presence of oxygen. For successful composting, sufficient oxygen should be provided to keep the system aerobic. This ensures that the composting proceeds rapidly and with minimal odor.

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.

ambient temperature Air temperature, i.e., the temperature of the air around the pile and not affected by the heat of the pile.

anaerobic Occurring in the absence of oxygen. Anaerobic composting proceeds slowly and is odiferous.


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.

biodegradability The potential of an organic substance to be broken down into simpler compounds or molecules through the action of microorganisms.

biodiversity In an environments created solely by nature, 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 post and disease control. However, when we only incorporate 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.

“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.

bulking agent Material, such as wood chips, added to compost primarily to help create good pore structure for air flow. Often provides part of carbon source as well.

bulk density The mass of a unit volume of soil, generally expressed in gm/cm3. The volume includes both solids and pores. Thus soils that are light and porous will have low bulk densities, while heavy or compact soils will have high bulk densities.


carbon-to-nitrogen ration (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.

carnivores Macroorganisms that feed on other animals. Includes ant, beetle, centipede, enchytraed, fly, mite, mole, scorpion, slug, snail, spider, springtail.

cellulose A polysaccharide composing cell walls.

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.

clippings Blades of grass cut off during the mowing process.

cold composting, cold pile When less attention is given to providing and maintaining optimum conditions for compost piles, the resulting environment that will attract psychrophilic bacteria, possibly mesophyllic bacteria, but not thermophilic bacteria. As the psychrophilic bacteria work, the compost pile will reach about 55 degrees F. This is the slow method of creating compost from a backyard pile, and can take as long as 6 months to 2 years to create compost. However, there is little maintenance other than occassionally turning the pile. This type of compost piles requires the least effort.

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 nutrients.

cytokinins Organic compounds acting like hormones in plants. Stimulates or alters cellular RNA resulting in a modification to plant development. Generally acts by affecting cellular division and differentiation into roots and shoots. This inhibits aging in the plant.

contaminant Unwanted material. Physical contaminants of compost include glass, plastic, and stones, and chemical contaminants include trace heavy metals and toxic compounds.

curing The last stage of composting that occurs after much of the readily metabolized material has been decomposed. Provides for additional stabilization and reduction of pathogens and allows further decomposition of cellulose and lignin.


decomposition The breakdown of organic matter through microbial action.

detritivores Macroorganisms that eat decaying matter. Includes ant, beetle, centipede, cricket, earthworm, earwig, enchytraeid worm, millipede, mite, scorpion, slug, snail, spider, springtail, termite, woodlice.

dripline The ground that lies directly below the outermost reaches of a trees branches.


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.


grasscycling Leaving grassclippings on your lawn to break down and add nutrients. You must mow a little more often so only short clippings are left on the lawn.

“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.

guano Manure, i.e., excretions, of bats and birds. Can be purchased after being dried and composted.


harvesting Removing compost from the composting environment for use in the landscape, lawn or garden.

heavy metals, trace metals Trace elements whose concentrations are regulated because of the potential for toxicity to humans, animals, or plants. Examples include chromium, copper, nickel, cadmium, lead, mercury, and zinc.

herbivores Macroorganisms that eat plants. Includes insect and beetle larva, grub, mouse, slug, snail, termite, woodchuck.

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, volume of 3 cubit feet, produce an environment that will attract psychrophilic, mesophyllic, and then thermophilic bacteria. As the thermophilic bacteria work, the compost pile will reach as high as 170 degrees F. This is the fastest method of creating compost from a backyard pile, and can take as little as 3 weeks if the pile is monitored and turned each time the temperature starts to fall.

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 sufars. It contains 3 - 5% nitrogen and 55 - 60% carbon. Humus is the slow-release food source for microorganism development. It is constantly being transformed into acids, enzymes and minerals and, therefore, must be constantly replenished for proper vegetative nutrition.


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 Substances 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". 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.

lignin A hard substance embedded in the cellulose of plant cell walls that provides support.

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. (See herbivores, detritivores, and carnivores)

mature compost The stabilized and sanitized product of composting;it has undergone decomposition and is in the process of stabilization. it is characterized as containing readily available forms of plant nutrients; it is low in phytotoxic acids.

mesophyllic 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.

metabolism Exchange of matter and energy between an organism and its environment and the transformation of this matter and energy within the organism.

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 Used interchangeably with "microorganism". (See microorganism)

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 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 compoinds, and finally into basic mineral elements.

moisture content Weight of water in material divided by weight of solids in material.

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.


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 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 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 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.


pathogen An organism including viruses, bacteria, fungi and protozoa capable of producing an infection or disease in a susceptible host.

permeability A measure of the rate at which water can percolate through soil.

persistance (i.e., chemical persistence) The length of time a chemical will remain essentially unchanged in the environment.

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.

phytotoxin An element or compound that injures plants.

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

polysaccharides Glue-like material formed by microorganisms in the process of mineralization, or breaking down organic matter. They are complex sugars which hold individual soil particles together. This creates larger particles known as aggregates.

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.


recycle Systems which may be run by private enterprise or local government to gather recyclable materials and remake them into similar or dissimilar products for market. Common examples are newspapers, glass, plastic, steel, and aluminum.

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.

reuse Practices which find alternate uses or alternate avenues for use of an item rather than expending energy to dispose it or alter its form by recycling or composting. Examples would be donating used books and magazines to a nursing home, using the fronts of Christmas cards to make new cards, using plastic margarine tubs to hold leftovers or craft supplies, donating clothing to charity.


sandy soils Low total quantity of pore space even though individual pores are large. Water retention is low.

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, encouraging the presence of microorganisms. From a legal standpoint, this is different than "fertilizer" and is not governed by the laws which regulate fertilizers.

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.

stability The degree to which the composted material can be stored or used without giving rise to nuisances, or can be applied to the soil without causing problems due to incomplete degradation of readily biodegradable materials.


thatch A layer of organic matter that begins to grow between the base of a plant and the soil. Usually discussed as a problem with lawns as dead roots and stems accumulate. Proponents of the organic philosophy say that in an organic program where soil has achieved a healthy balance, microorganisms are present to feed on mulched grass clippings and prevent thatch. However, if long grass (generally meaning growth of more than a week) is cut and mulched, there may be an excess of clippings which is too great for the existing population of microbes to handle in a timely way. Use your own judgment in determining how much is too much, then remove excess clippings from the yard and put them into the compost bin. Clippings of any length that are wet or matted should be removed from the lawn and placed in the compost bin.

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 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.

toxins Substances that cause a reduction of viability or functionality in living things.


vermicomposting, vermiculture Using redworms to compost food scraps, newspapers, and cardboard, yielding nutrient-rich castings.


windrow system Composting mixture is placed in elongated piles called windrows. These windrows are aerated naturally through the chimney effect, or by mechanically turning the piles with a machine or by forced aeration.


yard trimmings Grass clippings, leaves, and weeds and shrub and tree prunings six inches or less in diameter from a residence or business.