Composting Terms

Acidic Soil: Soil with a pH value higher than 7.0 (pH>7) is considered alkali and can be neutralized (pH of 7 being neutral) by addition of an acid (pH<7). Soil with a pH of higher than 10 (pH>10) is considered very alkaline. Alkalinity is caused by an increase in sodium compounds or sodium carbonates, which often occur as soil minerals break down. Alkaline soil has a low water infiltration capacity which means water tends to pool or stagnate on the surface. Alkaline soils can be neutralized or acidified by the addition of organic materials such as peat moss and compost or inorganic soil amendments such as sulfur which lower the soil pH. Gypsum is often used to “condition” alkaline soil because it improves the soil structure and water infiltration capacity while replacing the sodium in the soil compounds with calcium as it breaks down.

Actinomycetes: Also known as actinobacteria, actinomycetes are a form of bacteria existing mainly in soil. They form branches of thread-like filaments much like fungi and are important contributors to the decomposition process. They are especially effective at decomposing wood and hardy materials such as cellulose (tree and plant cell membranes) and chitin (fungi cell membranes). They also perform the valuable task of nitrogen fixing by forming cooperative relationships with plants and breaking down soil nitrogen so that it can be absorbed by the plants’ roots. Many of the nitrogen compounds in soil cannot be used by plants until they are first broken down by actinomycetes. Odors released by actinomycetes are what give compost and soil its “earthy” smell.

Aeration: Replenishing compost with oxygen by manual or mechanical means. The most popular way to aerate a compost pile is to manually turn it over with a fork, shovel, or compost turner. There are various compost containers that aerate by rolling, tumbling, flipping or performing other aerobic acrobatics. Aeration provides the actinomycetes and other aerobic bacteria, the workhorses of composting, with the oxygen they need to survive. As these organisms eat (decompose) organic matter and breathe air (aerobic) they produce heat and gases (mostly CO2) as by-products. This is the reason for higher temperatures at the center of compost piles where these bacteria thrive. Heat is an important ingredient in efficient composting as it increases the rate at which chemical transformation takes place. If a compost pile is well aerated it will not smell bad, as CO2, the main gas by-product of aerobic bacteria, is odorless. If a compost pile is not aerated regularly aerobic bacteria die off and anaerobic bacteria take over. Anaerobic bacteria produce the foul smelling gases such as ammonia, which make a pile stink.

Aerobic: Needing oxygen to survive and grow. Almost all animals, including humans, are aerobic organisms as well as most fungi, and many varieties of bacteria. Aerobic metabolism or respiration is a process by which organic and chemical compounds are broken down into useable energy by a reaction with oxygen. It is a form of chemical combustion that produces heat, water and carbon dioxide as by-products. The heat and moisture at the center of a compost pile are the noticeable by-products of bacteria that metabolize aerobically.

Anaerobic: Not needing oxygen to grow or survive. Most anaerobic organisms are bacteria. Many of these bacteria actually die in the presence of oxygen. Anaerobic bacteria are prevalent in swamps, bogs, cold lakes and animal (including human) digestive tracts. In compost piles, anaerobic bacteria proliferate if the pile is not aerated often or at all. Anaerobic bacteria do decompose the organic materials in compost, but they do so slowly and coolly. The bad smell that emanates from a poorly aerated pile is due to the higher nitrogen content. Anaerobic bacteria do not break down nitrogen which causes the stink (mostly ammonia) and also the slimy texture often present in unaerated compost piles.

Bacteria: Single celled microorganisms present in soil, water, organic material, animals and humans. Bacteria are found pretty much everywhere on earth, from deep sea trenches to human skin to yogurt, and they comprise the majority of organic life on the planet. There are approximately 40 million bacteria per teaspoon of soil and one million per milliliter of fresh water. They come in both beneficial and harmful, pathogenic forms. They help us humans digest our lunch and they help plants absorb nutrients by breaking down organic compounds into useable elemental particles. However, they are also responsible for human diseases such as syphilis and tuberculosis as well as common social faux pas including bad breath and body odor. Bacteria are crucial to the decomposition and nutrient recycling processes in both their aerobic and anaerobic varieties and are a friend and workhorse for every home composter.

Batch Composting: Composting in small amounts at a time using previously segregated materials is called batch composting. It includes composting in separate piles at the same time often with a “hot” pile and a “cold pile. Before batch composting, many gardeners start two separate piles of materials distinguishing one as a “brown” pile and the other as a “green” pile. The brown pile consists of dry materials such as dry leaves or lawn clippings. The green pile is made of kitchen and garden refuse, manures, and fertilizers. When batch composting, combine a larger amount from the “brown” (generally dry carbon-rich) pile with a smaller amount of the “green” (wet nitrogen-rich) pile into a separate pile or container then add some water and a compost activator or starter if needed. The ratio of “brown” to “green” is known as the C/N (carbon-nitrogen) ratio and is crucial in determining whether the pile is “hot” or “cold.” If the pile is aerated often and kept from drying out, you will have fresh, black, nutrient rich compost in as little as four to six weeks. You can also batch compost by simply adding fresh refuse or clippings to a bit of older compost, essentially using the older compost as a starter.

Bio-Solids: Bio-solids are the sludge by-product of wastewater treatment. Bio-solids are created when wastewater and sewage are treated to reduce pathogens and to break organic matter down into their more stable elemental forms. Bio-solids are often used as soil conditioners and fertilizers for agricultural crops. Pollutants are a concern with bio-solids. They often contain heavy metals that cannot be filtered out during treatment and may be saturated with the harmful chemicals used to treat sludge and “cure” it of pathogens.

Biodegradable: Biodegradable is a term used to describe materials that are able to break down or decompose into their smaller elemental compounds through interaction with the digestive enzymes and metabolic processes of living organisms. All organic material is biodegradable, even some artificial materials, so long as their chemical make up is similar enough to plants or animals that the microbes responsible for decomposition can effectively break them down into their constituent particles.

C/N Ratio: The carbon-to-nitrogen ratio in a compost pile. Whether a compost pile is considered “hot” or “cold,” is largely determined by the C/N ratio. The more nitrogen present, generally the “hotter,” “greener,” or more “wet” the pile will be. Nitrogen-rich materials for compost are the kitchen wastes such as food scraps, fruits and vegetables, blood and egg shells as well as fresh lawn clippings, fertilizers, and older compost. Carbon-rich materials are usually dry and “woody” such as dry leaves, sawdust, paper, teabags and coffee filters.

Cold “Slow” Pile: A cold or slow compost pile has a higher carbon-to-nitrogen ratio (C/N ratio) and takes longer to produce finished compost, anywhere from six months to two years. A cold pile is made mainly of carbon-rich dry or “brown” materials such as dry leaves, sawdust, and newspaper. Cold piles are less labor intensive but require larger amounts of both space and time. Because of the slow cool processes involved, cold piles produce compost that is more nitrogen rich. Since cold piles don’t reach the internal temperatures of hot “fast” piles, they tend to be weedier with more uncomposted material.

Compost: The end product of the decomposition of organic matter and biodegradable materials by aerobic and anaerobic microbes is known generally as compost. Compost is nutrient rich since during the decomposition process the larger organic compounds are broken down into their basic elemental particles that are easier for plants and other organisms to absorb. Compost serves as a great growing medium for agricultural and horticultural purposes as well as a soil conditioner. This dark brown to black soil/mulch can be easily made in the kitchen or back yard in a compost container or the more traditional pile form.

Compost Activator: An added catalyst used to start or increase the microbial decomposition in compost. Compost activators can be either nutrient rich soil amendments that feed already existing microbes or dormant bacteria and fungi. Compost activators range from enzymes and bacteria to products such as blood meal and nitrogen-rich fertilizers. Urine is sometimes used as a compost activator. It’s loaded with nitrogen and other nutrients and is cheap and abundant.

Composting: The aerobic or anaerobic decomposition of organic and biodegradable material resulting in a nutrient-rich growing medium and soil amendment. Composting can be performed in the backyard or kitchen and is an important way for people to take charge in recycling food and consumer wastes into a reusable and green energy source for growing food or flowers.

Decomposition: The process by which the organic matter of dead organisms decays or breaks down into constituent particles and elemental compounds. Decomposition is vital to new growth and the continued survival of living organisms since it is the main process by which nutrients are recycled in the natural world.

Double Digging: A process of developing a loose, deep garden bed with good aeration and drainage by first removing the topsoil, then loosening the subsoil, and finally replacing the removed topsoil. Double digging is an ideal form of garden bed preparation when planting carrots, beets, potatoes, onions and other root crops as well as a way to improve the overall health of the garden. The increased oxygen and water penetration from double digging allows worms and microbes — vital to decomposition and plants’ absorption of nutrients through nitrogen-fixing — to thrive.

Enzymes: Protein molecules that act as catalysts in chemical reactions. Enzymes dramatically speed up the rate at which organic compounds decompose. Most enzymes are very specific, acting only on certain molecules. Animal saliva and GI tracts utilize enzymes to breakdown and digest food. Bacteria and fungi in the soil and air use enzymes to dissolve and decompose organic material during the process of decay thereby recycling and dispersing nutrients from dead organisms and reintegrating them into the food chain.

Fungal Disease: Respiratory and skin diseases resulting from inhalation or direct contact with fungal spores in soil and compost. Overly wet soil (40% water) and compost are the usual causes of respiratory fungal diseases such as “farmers’ lung.” Symptoms usually occur 4-6 hours after exposure and are flu-like with a high fever and aches lasting for 12 hours or more. Skin infection may result in rashes and sores.s

Green Manure: Also known as cover crops, green manure crops are planted when land is fallow, for instance during fall or winter, and used to suppress weeds and bring nutrients to the surface. It is then plowed under before planting in order to increase biomass within the soil. Green manure is often used to recondition soil that has been over worked and is a useful tool in agricultural crop rotation. Legumes such as clover and vetch are popular green manures because they encourage the growth of nitrogen-fixing bacteria that break down nitrogen from the soil and atmosphere into forms useable by plants.

Growing Medium: A growing medium is very simply anything a plant can grow in. Soil, obviously, is the most common growing medium but there are also a wide variety man-made and natural products that plants will grow in. Coco-fiber, rock wool, perlite, vermiculite, sawdust, water, and even air are all examples of growing mediums. What the plant needs and what grow system is being used are the major determiners of what growing medium is appropriate.

Heavy Soil: Dense soils made of silt and clay that are often very fertile but require soil amendments to improved structure as well as oxygen and water penetration.

Hot “Active” Pile: A compost pile in which the internal temperature reaches a range between 110 and 160 F. Hot piles are the result of aerobic bacteria which thrive at higher temperatures and also generate heat as a by-product of their metabolism. Frequent aeration keeps the aerobic bacteria working and the temperature up as they consume the decaying organic matter. Hot piles work fast and can produce nutrient-rich compost in as little as 4-6 weeks compared with the 6 months to 2 years it takes a cold pile to achieve the same result.

Humus: Decayed organic matter usually seen as dark brown or black soil. Humus refers to organic material that has reached a point of stability in which it can decay no further. Fully-finished compost is humus. It is rich in nutrients and makes for a very fertile growing medium. Humus comes in different varieties depending upon the decomposed material that makes it. These varieties are very commonly used as soil amendments. Topsoil is an example of humus found nearly everywhere.

Inoculant: Beneficial fungi or bacteria added to soil to either destroy plant pathogens, form cooperative relationships with plant roots so they can absorb more nutrients, or to break down soil compounds into elemental particles that are more easily used by plants. Common soil inoculants are microbes called rhizo-bacteria which act as nitrogen-fixers by capturing and breaking down nitrogen in soils and air.

Leachate: A liquid solution resulting from bodies of decomposing matter such as compost piles and landfills when water is added. Bacteria, fungi, nutrients and pollutants can all be suspended in a leachate solution depending on the original ingredients. In composting, leachate is commonly referred to as compost tea. This is due to the process of brewing or steeping compost in water in order to create a leachate that is higher in nutrients and microbes than would naturally occur. Leachate or compost tea is often applied to soils in order to increase the microbial presence so that decomposition of organic matter such as leaves is sped up.

Lime: Generally refers to inorganic materials made up predominantly of calcium such as gypsum. Specifically, lime refers to calcium oxide (CaO), also known as quick lime, which is highly caustic. Lime made from burning shells such as oyster shell lime are predominantly made of calcium carbonate and is commonly used as a soil amendment. Lime as a soil amendment is used to raise soil pH in order to make the soil more alkaline and is sometimes used to improve soil structure. When composting, it is important not to throw fresh ashes on the compost as they will act as quick lime destroying all microbial life within the pile.

Loam: An ideal soil for gardening and agriculture made of a combination of sand, silt and clay in roughly equal proportions. Loam is high in nutrients and humus and is able to retain more water than other soils while still allowing it to flow freely. Loam may come in different varieties usually described by the different proportions of constituent particles such as sandy loam, clay loam, silty loam, or sandy clay loam, etc. Gardeners often create loam from their existing soil with the use of soil amendments and compost.

Macro-Nutrients: Elemental nutrients needed by organisms in relatively large proportions. Macronutrients that plants rely on are carbon, oxygen, and hydrogen which are obtained from air and water and nitrogen, phosphorous, and potassium (N-P-K) which are absorbed from the soil by the plant’s roots.

Mesophiles: Organisms which thrive in moderate temperature environments ranging from 77 to 104 F. Mesophiles are generally bacteria and other microbes living in soil, food, and animals. Beer, yogurt, and cheese are examples of foods that rely on mesophilic microorganisms for their preparation.

Micro-nutrients: Elemental nutrients needed by organisms in relatively small proportions. In plants and animals, micronutrients are needed for healthy growth and bodily functions. Micronutrients needed by plants include iron, zinc, molybdenum, copper, cobalt, manganese, sulfur, chlorine and others. Chlorine for instance is important for a plant’s ability to perform photosynthesis. Many plant ailments are due to a lack of certain vital micronutrients. One of the functions of fertilizers, compost and other soil amendments is to increase the amount and variety of micronutrients in soil to improve overall plant health.

Microorganism: Microscopic organisms, also called microbes, not visible to the naked eye. Bacteria and fungi are common microorganisms. Microscopic plants such as algae as well as microscopic worms and parasites are also considered to be microorganisms.

Mulch: A soil covering used in gardening and agriculture to protect soil from the extremes of weather and climate by helping conserve soil moisture and moderating temperatures. Mulch helps soil retain water from rainfall and heat absorbed during daylight. It also protects soil against direct sunlight therefore keeping soil moist and cool during the hot summer months. Weed prevention is a major use for mulch. It both blocks sunlight to unwelcome weeds and smothers the seeds before they start. Mulch is also great for erosion prevention and protecting soil from the damaging aspects of heavy rains. Common materials used for mulch are: hay, straw, grass clippings, bark, sawdust, wood chips, newspaper, and cardboard. Rocks, gravel and plastic are also often used as mulch. If compost is used as mulch, it is necessary that it is fully composted and that all weed seeds have been killed; otherwise, it will actually contribute more weeds to the area.

N-P-K: Stands for Nitrogen, Phosphorus, and Potassium (aka potash) the macronutrients necessary for plants to survive and grow. Usually listed on fertilizers and soil amendments with a number, for example 7-9-5, representing the percentage by weight of each nutrient contained in the product. Nitrogen is the macronutrient necessary for vegetative growth above ground. Nitrogen, the most important macronutrient, promotes healthy stem and leaf growth and provides for rich dark green foliage. Phosphorus is the second most important macronutrient and is vital to root growth, fruit and flower development, and disease prevention. Potassium is important for strong, healthy plants. It contributes to disease resistance and protects plants from cold as well as water loss during periods of heat and drought.

Organic: A term used to describe certain agricultural and food production methods which do not use toxic fertilizers and pesticides, genetic engineering, synthetic hormone stimulation, antibiotics and other practices such as irradiation and the spreading of treated sewage. Farmers, food producers and processors must meet nationally regulated standards in order to be considered organic. Products such as fertilizers, soil amendments and pesticides must also meet federal guidelines if they are to be labeled organic and given the “USDA Organic” seal. There is some confusion with the term organic as an opposite of commercial. The proper antithesis to organic is chemical or synthetic since for instance both organic and chemical fertilizers are sold commercially.

Organic Gardening: The practice of growing fruits, vegetables, flowers and other plants without the use of chemicals or synthetic products. Organic gardening philosophies and techniques vary. Some believe in only using plants and products that occur naturally in the local environment. Others are more liberal using any product so long as it is organic and is not harmful. Still others consider organic gardening to be an integral part of sustainable living, taking in to account not only if the product is organic but if things such as the fossil fuels were used in shipping and the product’s effects on the local ecosystem. Generally organic gardening is the art of growing plants using organic products such as compost, natural soil amendments, natural pesticides, and beneficial microbes and insects.

Pest: Any unwanted or harmful organism that is dangerous, damaging or irritating. In gardening, pests are usually animals, insects and microbes which feed or otherwise act as parasites on the crops being grown; for example, codling moths on apples or aphids on house plants and flowers. There are many pesticides on the market, both organic and chemical, which can eliminate or control pests. Beneficial insects and microbes are used as natural pest controls.

Pesticide: Any substance or solution used to control or kill pests. Pesticides come in many forms, from chemical and organic solutions and sprays to biological agents such as microbes and viruses to predatory insects such as praying mantis. Pests vary and pesticides are often specific to certain species killing, say, grasshoppers but not spiders or other insects. Many chemical pesticides are toxic to humans and animals and should be used with caution.

pH: The measure of the acidity or alkalinity of a substance or solution. Technically pH measures the activity of dissolved hydrogen within a substance. pH is a relative measurement with “pure” water being neutral at pH 7.0. A pH lower than 7.0 is considered acidic and a pH higher than 7.0 is considered alkaline or basic. Adding an alkaline to an acidic substance will raise its pH making it more neutral or alkaline. An acid added to an alkaline substance will lower the pH and make the substance more neutral or acidic.

Potting Mix: A mixture of soil and other ingredients used to grow plants in containers or a garden. A common potting mix is a mixture of compost (for nutrients), peat moss (for biomass), sand (for soil structure), and perlite (for drainage). Different plants need different soil structures, nutrients, and pH measures so it is often necessary for a gardener to create his own potting mix. Soil amendments, fertilizers and homemade compost are ingredients one can use to modify an existing potting mix or create an entirely new one depending on the specific needs of the plant.

Propagation: Distributing plants either by natural or artificial means. Plants can be propagated by both sexual and asexual reproduction. Sexual reproduction in plants produces seeds or spores which can be propagated by manually planting or sowing them or letting wind and other natural forces distribute them. Vegetative or asexual reproduction happens when a plant propagates by producing a clone of itself. Gardeners take advantage of vegetative reproduction when grafting or starting new plants from cuttings. An example of propagation by asexual reproduction is planting potatoes by sowing the “eyes.”

Psychrophiles: Organisms that survive, grow and thrive in cold temperatures generally described as below 70F. Obviously these organisms are fairly ubiquitous as the majority of the earth’s climates experience temperatures in this range. Psychrophilic microorganisms exist in alpine and arctic soils as well as in trenches miles below the surface of the ocean.

Sheet Composting: Composting by spreading a thin layer of organic material across a large area such as a garden bed. With sheet composting, there is no need to create a compost pile. Grass and garden clippings make great materials for sheet composting and since they compost slowly they offer many of the same benefits as mulch by protecting soil from weather and erosion. Shredding or chopping up the materials can speed up the process when sheet composting.

Soil Amendment: Any material added to soil to improve or change its characteristics. Soil amendments are utilized when physical properties such as structure, aeration, nutrient and water retention, and drainage need improvement. The main function of soil amendments is to provide a better environment for the roots so they can grow and absorb nutrients more easily. Compost is a common soil amendment as it improves soil structure and nutrients. Other common soil amendments are greensand, bloodmeal, bonemeal, elemental sulfur, glacial rock dust, and various fertilizers.

Soil Test: Measuring soil for pH and N-P-K ratios, often done in labs or with home soil test kits. Soil tests are important in determining what plants work best in a specific native soil and for understanding any nutrient and pH deficiency soils may have. Gardeners often test soil regularly to optimize a soil’s properties depending on the plants being grown. When deficiencies or nutrient needs are determined gardeners adjust the soils physical properties by adding various soil amendments.

Soil-less Mix: A mixture used for container gardening that contains no soil. Soil-less mixes are commonly made of peat moss, vermiculite or perlite, and fertilizers. Sand, compost and other mineral soil amendments are often used in soil-less mix recipes.

Thermophiles: Organisms that grow and thrive at high temperatures generally described as above 110F. Thermophiles are commonly found in decomposing organic material such as compost and peat moss as well as in natural hot spots such as geothermal hot springs and deep sea vents. Thermophiles can withstand intense heat and actually utilize this heat to help break down compounds which they metabolize. Many thermophiles require elemental sulfur to survive.

Tilth: The physical properties and fitness of a soil for a specific plant or crop. Generally tilth means tilled earth, but to gardeners, it is the overall health or needs of a soil when growing certain plants. A soil with good tilth is easily worked, has a good pH and structure, and allows for maximum aeration, nutrient and water retention as well as easy root penetration. Soils deemed as having poor tilth can be improved with elemental soil amendments, compost, and fertilizers.

Topdressing: Application of a thin layer soil mix or compost to a lawn or garden. Topdressing improves soil quality gradually as each successive layer builds upon the last. It is a method used to even out bumpy or uneven lawns and stimulates grass to grow new roots resulting in a thicker lawn cover. Topdressing is similar to sheet composting in application except that the material used is fully decomposed.

Vermicomposting: Using worms to compost organic material. Vermicompost is generally richer in nutrients than regular compost due to a higher presence of microbes and the nutrient-retaining properties of worm castings. Red wiggler worms are the most common worms used for composting though European earthworms are sometimes used. Worms are not the only organisms involved in vermicomposting; bacteria and fungi, as in regular composting, also contribute to the process. Red wiggler worms are commonly found in nature in soil, manure and rotting vegetation. These worms adapt easily to living in worm bins since they naturally survive off of decaying organic matter and live close to the surface. Vermicomposting requires less physical labor than normal composting since the worms do most of the aerating. In large scale operations, a windrow system is often used. Bins are the most common method for vermicomposting on a small scale.

Weed: Any plant that is unwanted or considered to be a nuisance. To many people weeds are simply an eyesore while to others they are problematic because they bloc sunlight and rob other plants of nutrients.

Windrow System: Long, open-air piles, windrows consist of organic matter or compost that is aerated manually or mechanically. The windrow system is most commonly used for composting on a large scale such as on a farm. Windrows are built from a mixture of brown (carbon-rich) and green (nitrogen-rich) materials in ratios that optimize air and water infiltration and microbial life just like a regular compost pile. On a large scale, windrow compost turners or backhoes are used to turn over and aerate the windrows. On a small-garden scale, a shovel or pitchfork and some physical work suffices.

Worm Casting: Worm excrement that is nutrient-rich with excellent moisture retention often used as a natural fertilizer and soil amendment. Worm castings contain mucus that helps retain nutrients so they are not washed away during waterings or rain. They also stimulate microbial life within the soil, which aids decomposition and overall soil health. As a soil amendment, worm castings are often used not only for nutrients but also to improve soil structure and oxygen/water penetration.