Composting Basics

Managing living systems usually goes better when our methods imitate nature’s. Here’s an example of what happens when we don’t.

People who keep tropical fish in home aquariums are informed that to avoid numerous fish diseases they must maintain sterile conditions. Whenever the fish become ill or begin dying, the hobbyist is advised to put antibiotics or mild antiseptics into the tank, killing off most forms of microlife. But nature is not sterile. Nature is healthy.

Like many an apartment dweller, in my twenties I raised tropical fish and grew house plants just to have some life around. The plants did fine; I guess I’ve always had a green thumb. But growing tired of dying fish and bacterial blooms clouding the water, I reasoned that none of the fish I had seen in nature were diseased and their water was usually quite clear. Perhaps the problem was that my aquarium had an overly simplified ecology and my fish were being fed processed, dead food when in nature the ecology was highly complex and the fish were eating living things. So I bravely attempted the most radical thing I could think of; I went to the country, found a small pond and from it brought home a quart of bottom muck and pond water that I dumped into my own aquarium. Instead of introducing countless diseases and wiping out my fish, I actually had introduced countless living things that began multiplying rapidly. The water soon became crystal clear. Soon the fish were refusing to eat the scientifically formulated food flakes I was supplying. The profuse variety of little critters now living in the tank’s gravel ate it instead. The fish ate the critters and became perfectly healthy.

When the snails I had introduced with the pond mud became so numerous that they covered the glass and began to obscure my view, I’d crush a bunch of them against the wall of the aquarium and the fish would gorge on fresh snail meat. The angelfish and guppies especially began to look forward to my snail massacres and would cluster around my hand when I put it into the tank. On a diet of living things in a natural ecology even very difficult species began breeding.

Organic and biological farmers consider modern “scientific” farming practices to be a similar situation. Instead of imitating nature’s complex stability, industrial farmers use force, attempting to bend an unnaturally simplified ecosystem to their will. As a result, most agricultural districts are losing soil at a non-sustainable rate and produce food of lowered nutritional content, resulting in decreasing health for all the life forms eating the production of our farms. Including us.

I am well aware that these condemnations may sound quite radical to some readers. In a post this brief I cannot offer adequate support for my concerns about soil fertility and the nation’s health. I especially recommend the works of William Albrecht, Weston Price, Sir Robert McCarrison, and Sir Albert Howard.

Making Humus

Before we ask how to compost, since nature is maximally efficient perhaps it would benefit us to first examine how nature goes about returning organic matter to the soil from whence it came. If we do nearly as well, we can be proud.

Where nature is allowed to operate without human intervention, each place develops a stable level of biomass that is inevitably the highest amount of organic life that site could support. Whether deciduous forest, coniferous forest, prairie, even desert, nature makes the most of the available resources and raises the living drama to its most intense and complex peak possible. There will be as many mammals as there can be, as many insects, as many worms, as many plants growing as large as they can get, as much organic matter in all stages of decomposition and the maximum amount of relatively stable humus in the soil. All these forms of living and decomposing organisms are linked in one complex system; each part so closely connected to all the others that should one be lessened or increased, all the others change as well.

The efficient decomposition of leaves on a forest floor is a fine example of what we might hope to achieve in a compost pile. Under the shade of the trees and mulched thickly by leaves, the forest floor usually stays moist. Although the leaves tend to mat where they contact the soil, the wet, somewhat compacted layer is thin enough to permit air to be in contact with all of the materials and to enter the soil.

Living in this very top layer of fluffy, crumbly, moist soil mixed with leaf material and humus, are the animals that begin the process of humification. Many of these primary decomposers are larger, insect-like animals commonly known to gardeners, including the wood lice that we call pill bugs because they roll up defensively into hard armadillo-like shells, and the highly intrusive earwigs my daughter calls pinch bugs. There are also numerous types of insect larvae busily at work.

A person could spend their entire life trying to understand the ecology of a single handful of humus-rich topsoil. For a century now, numerous soil biologists have been doing just that and still the job is not finished. Since gardeners, much less ordinary people, are rarely interested in observing and naming the tiny animals of the soil, especially are we disinterested in those who do no damage to our crops, soil animals are usually delineated only by Latin scientific names. The variations with which soil animals live, eat, digest, reproduce, attack, and defend themselves fills whole sections of academic science libraries.

During the writing of this book I became quite immersed in this subject and read far more deeply into soil biology and microbiology than I thought I ever would. Even though this area of knowledge has amused me, I doubt it will entertain most of you. If it does, I recommend that you first consult specialist source materials listed in the bibliography for an introduction to a huge universe of literature.

I will not make you yawn by mentioning long, unfamiliar Latin names. I will not astonish you with descriptions of complex reproductive methods and beautiful survival strategies. Gardeners do not really need this information. But managing the earth so that soil animals are helped and not destroyed is essential to good gardening. And there are a few qualities of soil animals that are found in almost all of them. If we are aware of the general characteristics of soil animals we can evaluate our composting and gardening practices by their effect on these minuscule creatures.

Compared to the atmosphere, soil is a place where temperature fluctuations are small and slow. Consequently, soil animals are generally intolerant to sudden temperature changes and may not function well over a very wide range. That’s why leaving bare earth exposed to the hot summer sun often retards plant growth and why many thoughtful gardeners either put down a thin mulch in summer or try to rapidly establish a cooling leaf canopy to shade raised beds. Except for a few microorganisms, soil animals breathe oxygen just like other living things and so are dependent on an adequate air supply. Where soil is airless due to compaction, poor drainage, or large proportions of very fine clay, soil animals are few in number.

The soil environment is generally quite moist; even when the soil seems a little dryish the relative humidity of the soil air usually approaches 100 percent. Soil animals consequently have not developed the ability to conserve their body moisture and are speedily killed by dry conditions. When faced with desiccation they retreat deeper into the soil if there is oxygen and pore spaces large enough to move about. So we see another reason why a thin mulch that preserves surface moisture can greatly increase the beneficial population of soil animals. Some single-cell animals and roundworms are capable of surviving stress by encysting themselves, forming a little “seed” that preserves their genetic material and enough food to reactivate it, coming back to life when conditions improve. These cysts may endure long periods of severe freezing and sometimes temperatures of over 150 degree F.

Inhabitants of leaf litter reside close to the surface and so must be able to experience exposure to dryer air and light for short times without damage. The larger litter livers are called primary decomposers. They spend most of their time chewing on the thick reserve of moist leaves contacting the forest floor. Primary decomposers are unable to digest the entire leaf. They extract only the easily assimilable substances from their food: proteins, sugars and other simple carbohydrates and fats. Cellulose and lignin are the two substances that make up the hard, permanent, and woody parts of plants; these materials cannot be digested by most soil animals. Interestingly, just like in a cow’s rumen, there are a few larvae whose digestive tract contains cellulose-decomposing bacteria but these larvae have little overall effect.

After the primary consumers are finished the leaves have been mechanically disintegrated and thoroughly moistened, worked over, chewed to tiny pieces and converted into minuscule bits of moist excrement still containing active digestive enzymes. Many of the bacteria and fungi that were present on the leaf surfaces have passed through this initial digestion process alive or as spores waiting and ready to activate. In this sense, the excrement of the primary decomposers is not very different than manure from large vegetarian mammals like cows and sheep although it is in much smaller pieces.

Digestive wastes of primary decomposers are thoroughly inoculated with microorganisms that can consume cellulose and lignin. Even though it looks like humus, it has not yet fully decomposed. It does have a water-retentive, granular structure that facilitates the presence of air and moisture throughout the mass creating perfect conditions for microbial digestion to proceed.

This excrement is also the food for a diverse group of nearly microscopic soil animals called secondary decomposers. These are incapable of eating anything that has not already been predigested by the primary decomposers. The combination of microbes and the digestive enzymes of the primary and secondary decomposers breaks down resistant cellulose and to some degree, even lignins. The result is a considerable amount of secondary decomposition excrement having a much finer crumb structure than what was left by the primary decomposers. It is closer to being humus but is still not quite finished.

Now comes the final stage in humus formation. Numerous species of earthworms eat their way through the soil, taking in a mixture of earth, microbes, and the excrement of soil animals. All of these substances are mixed together, ground-up, and chemically recombined in the worm’s highly active and acidic gut. Organic substances chemically unite with soil to form clay/humus complexes that are quite resistant to further decomposition and have an extraordinarily high ability to hold and release the very nutrients and water that feed plants. Earthworm casts (excrement) are mechanically very stable and help create a durable soil structure that remains open and friable, something gardeners and farmers call good tilth or good crumb. Earthworms are so vitally important to soil fertility and additionally useful as agents of compost making.

Let’s underline a composting lesson to be drawn from the forest floor. In nature, humus formation goes on in the presence of air and moisture. The agents of its formation are soil animals ranging in complexity from microorganisms through insects working together in a complex ecology. These same organisms work our compost piles and help us change crude vegetation into humus or something close to humus. So, when we make compost we need to make sure that there is sufficient air and moisture.

Decomposition is actually a process of repeated digestions as organic matter passes and repasses through the intestinal tracts of soil animals numerous times or is attacked by the digestive enzymes secreted by microorganisms. At each stage the vegetation and decomposition products of that vegetation are thoroughly mixed with animal digestive enzymes. Soil biologists have observed that where soil conditions are hostile to soil animals, such as in compacted fine clay soils that exclude air, organic matter is decomposed exclusively by microorganisms. Under those conditions virtually no decomposition-resistant humus/clay complexes form; almost everything is consumed by the bacterial community as fuel. And the non-productive soil is virtually devoid of organic matter.

Sir Albert Howard has been called the ‘father of modern composting.’ His first composting book (1931) The Waste Products of Agriculture, stressed the vital importance of animal digestive enzymes from fresh cow manure in making compost. When he experimented with making compost without manure the results were less than ideal. Most gardeners cannot obtain fresh manure but fortunately soil animals will supply similar digestive enzymes. Later on when we review Howard’s Indore composting method we will see how brilliantly Sir Albert understood natural decomposition and mimicked it in a composting method that resulted in a very superior product.

At this point I suggest another definition for humus. Humus is the excrement of soil animals, primarily earthworms, but including that of some other species that, like earthworms, are capable of combining partially decomposed organic matter and the excrement of other soil animals with clay to create stable soil crumbs resistant to further decomposition or consumption.

Nutrients in the Compost Pile

Some types of leaves rot much faster on the forest floor than others. Analyzing why this happens reveals a great deal about how to make compost piles decompose more effectively.

Leaves from leguminous (in the same botanical family as beans and peas) trees such as acacia, carob, and alder usually become humus within a year. So do some others like ash, cherry, and elm. More resistant types take two years; these include oak, birch, beech, and maple. Poplar leaves, and pine, Douglas fir, and larch needles are very slow to decompose and may take three years or longer. Some of these differences are due to variations in lignin content which is highly resistant to decomposition, but speed of decomposition is mainly influenced by the amount of protein and mineral nutrients contained in the leaf.

Plants are composed mainly of carbohydrates like cellulose, sugar, and lignin. The element carbon is by far the greater part of carbohydrates [carbo(n)hydr(ogen)ates] by weight. Plants can readily manufacture carbohydrates in large quantities because carbon and hydrogen are derived from air (C02) and water (H2O), both substances being available to plants in almost unlimited quantities.

Sugar, manufactured by photosynthesis, is the simplest and most vital carbohydrate. Sugar is “burned” in all plant cells as the primary fuel powering all living activities. Extra sugar can be more compactly stored after being converted into starches, which are long strings of sugar molecules linked together. Plants often have starch-filled stems, roots, or tubers; they also make enzymes capable of quickly converting this starch back into sugar upon demand. We home-brewers and bakers make practical use of a similar enzyme process to change starches stored in grains back to sugar that yeasts can change into alcohol.

C/N of Various Tree Leaves/Needles

The protein content of tree leaves is very similar to their ratio of carbon (C) compared to nitrogen (N)

Sometimes plants store food in the form of oil, the most concentrated biological energy source. Oil is also constructed from sugar and is usually found in seeds. Plants also build structural materials like stem, cell walls, and other woody parts from sugars converted into cellulose, a substance similar to starch. Very strong structures are constructed with lignins, a material like cellulose but much more durable. Cellulose and lignins are permanent. They cannot be converted back into sugar by plant enzymes. Nor can most animals or bacteria digest them.

Certain fungi can digest cellulose and lignin, as can the symbiotic bacteria inhabiting a cow’s rumen. In this respect the cow is a very clever animal running a cellulose digestion factory in the first and largest of its several stomachs. There, it cultures bacteria that eat cellulose; then the cow digests the bacteria as they pass out of one stomach and into another.

Plants also construct proteins, the vital stuff of life itself. Proteins are mainly found in those parts of the plant involved with reproduction and photosynthesis. Protein molecules differ from starches and sugars in that they are larger and amazingly more complex. Most significantly, while carbohydrates are mainly carbon and hydrogen, proteins contain large amounts of nitrogen and numerous other mineral nutrients.

Proteins are scarce in nature. Plants can make them only in proportion to the amount of the nutrient, nitrogen, that they take up from the soil. Most soils are very poorly endowed with nitrogen. If nitrate-poor, nutrient-poor soil is well-watered there may be lush vegetation but the plants will contain little protein and can support few animals. But where there are high levels of nutrients in the soil there will be large numbers of animals, even if the land is poorly watered and grows only scrubby grasses—verdant forests usually feed only a few shy deer while the short grass semi-desert prairies once supported huge herds of grazing animals.

Ironically, just as it is with carbon, there is no absolute shortage of nitrogen on Earth. The atmosphere is nearly 80 percent nitrogen. But in the form of gas, atmospheric nitrogen is completely useless to plants or animals. It must first be combined chemically into forms plants can use, such as nitrate (NO3) or ammonia (NH3). These chemicals are referred to as “fixed nitrogen.”

Nitrogen gas strongly resists combining with other elements. Chemical factories fix nitrogen only at very high temperatures and pressures and in the presence of exotic catalysts like platinum or by exposing nitrogen gas to powerful electric sparks. Lightning flashes can similarly fix small amounts of nitrogen that fall to earth dissolved in rain.

And certain soil-dwelling microorganisms are able to fix atmospheric nitrogen. But these are abundant only where the earth is rich in humus and minerals, especially calcium. So in a soil body where large quantities of fixed nitrogen are naturally present, the soil will also be well-endowed with a good supply of mineral nutrients.

Most of the world’s supply of combined nitrogen is biologically fixed at normal temperatures and standard atmospheric pressure by soil microorganisms. We call the ones that live freely in soil “azobacteria” and the ones that associate themselves with the roots of legumes “rhizobia.” Blue-green algae of the type that thrive in rice paddies also manufacture nitrate nitrogen. We really don’t know how bacteria accomplish this but the nitrogen they “fix” is the basis of most proteins on earth.

All microorganisms, including nitrogen-fixing bacteria, build their bodies from the very same elements that plants use for growth. Where these mineral elements are abundant in soil, the entire soil body is more alive and carries much more biomass at all levels from bacteria through insects, plants, and even mammals.

Should any of these vital nutrient substances be in short supply, all biomass and plant growth will decrease to the level permitted by the amount available, even though there is an overabundance of all the rest. The name for this phenomena is the “Law of Limiting Factors.” The concept of limits was first formulated by a scientist, Justus von Liebig, in the middle of the last century. Although Liebig’s name is not popular with organic gardeners and farmers because misconceptions of his ideas have led to the widespread use of chemical fertilizers, Liebig’s theory of limits is still good science.

Liebig suggested imagining a barrel being filled with water as a metaphor for plant growth: the amount of water held in the barrel being the amount of growth. Each stave represents one of the factors or requirements plants need in order to grow such as light, water, oxygen, nitrogen, phosphorus, copper, boron, etc. Lowering any one stave of the barrel, no matter which one, lessens the amount of water that can be held and thus growth is reduced to the level of the most limited growth factor.

For example, one essential plant protein is called chlorophyll, the green pigment found in leaves that makes sugar through photosynthesis. Chlorophyll is a protein containing significant amounts of magnesium. Obviously, the plant’s ability to grow is limited by its ability to find enough fixed nitrogen and also magnesium to make this protein.

Animals of all sizes from elephants to single cell microorganisms are primarily composed of protein. But the greatest portion of plant material is not protein, it is carbohydrates in one form or another. Eating enough carbohydrates to supply their energy requirements is rarely the survival problem faced by animals; finding enough protein (and other vital nutrients) in their food supply to grow and reproduce is what limits their population. The numbers and health of grazing animals is limited by the protein and other nutrient content of the grasses they are eating, similarly the numbers and health of primary decomposers living on the forest floor is limited by the nutrient content of their food. And so is the rate of decomposition. And so too is this true in the compost pile.

The protein content of vegetation is very similar to its ratio of carbon (C) compared to nitrogen (N). Quick laboratory analysis of protein content is not done by measuring actual protein itself but by measuring the amount of combined nitrogen the protein gives off while decomposing. Acacia, alder, and leaves of other proteinaceous legumes such as locust, mesquite, scotch broom, vetch, alfalfa, beans, and peas have low C/N ratios because legume roots uniquely can shelter clusters of nitrogen-fixing rhizobia. These microorganisms can supply all the nitrate nitrogen fast-growing legumes can use if the soil is also well endowed with other mineral nutrients rhizobia need, especially calcium and phosphorus. Most other plant families are entirely dependent on nitrate supplies presented to them by the soil. Consequently, those regions or locations with soils deficient in mineral nutrients tend to grow coniferous forests while richer soils support forests with more protein in their leaves. There may also be climatic conditions that favor conifers over deciduous trees, regardless of soil fertility.

It is generally true that organic matter with a high ratio of carbon to nitrogen also will have a high ratio of carbon to other minerals. And low C/N materials will contain much larger amounts of other vital mineral nutrients. When we make compost from a wide variety of materials there are probably enough quantity and variety of nutrients in the plant residues to form large populations of humus-forming soil animals and microorganisms. However, when making compost primarily with high C/N stuff we need to blend in other substances containing sufficient fixed nitrogen and other vital nutrient minerals. Otherwise, the decomposition process will take a very long time because large numbers of decomposing organisms will not be able to develop.

C/N of Compostable Materials

+/-6:1 +/-12:1 +/-25:1 +/-50:1 +/-100:1
Bone Meal Vegetables Summer grass cornstalks (dry) Sawdust
Meat scraps Garden weeds Seaweed Straw (grain) Paper
Fish waste Alfalfa hay Legume hulls Hay (low quality) Tree bark
Rabbit manure Horse manure Fruit waste Bagasse
Chicken manure Sewage sludge Hay (top quality) Grain chaff
Pig manure Silage Corn cobs
Seed meal Cow manure Cotton mill waste

The lists in this table of carbon/nitrogen ratios are broken out as general ranges of C/N. It has long been an unintelligent practice of garden-level books to state “precise” C/N ratios for materials. One substance will be “23:1” while another will be “25:1.” Such pseudoscience is not only inaccurate but it leads readers into similar misunderstandings about other such lists, like nitrogen contents, or composition breakdowns of organic manures, or other organic soil amendments. Especially misleading are those tables in the back of many health and nutrition books spelling out the “exact” nutrient contents of foods. There is an old saying about this: ‘There are lies, then there are damned lies, and then, there are statistics. The worse lies of all can be statistics.’

The composition of plant materials is very dependent on the level and nature of the soil fertility that produced them. The nutrition present in two plants of the same species, even in two samples of the exact same variety of vegetable raised from the same packet of seed can vary enormously depending on where the plants were grown. William Albrecht, chairman of the Soil Department at the University of Missouri during the 1930s, was, to the best of my knowledge, the first mainstream scientist to thoroughly explore the differences in the nutritional qualities of plants and to identify specific aspects of soil fertility as the reason why one plant can be much more nutritious than another and why animals can be so much healthier on one farm compared to another. By implication, Albrecht also meant to show the reason why one nation of people can be much less healthy than another. Because his holistic outlook ran counter to powerful vested interests of his era, Albrecht was professionally scorned and ultimately left the university community, spending the rest of his life educating the general public, especially farmers and health care professionals.

Summarized in one paragraph, Albrecht showed that within a single species or variety, plant protein levels vary 25 percent or more depending on soil fertility, while a plant’s content of vital nutrients like calcium, magnesium, and phosphorus can simultaneously move up or down as much as 300 percent, usually corresponding to similar changes in its protein level. Albrecht also discovered how to manage soil in order to produce highly nutritious food. Chapter Eight has a lot more praise for Dr. Albrecht. There I explore this interesting aspect of gardening in more detail because how we make and use organic matter has a great deal to do with the resulting nutritional quality of the food we grow.

Imagine trying to make compost from deficient materials such as a heap of pure, moist sawdust. What happens? Very little and very, very slowly. Trees locate most of their nutrient accumulation in their leaves to make protein for photosynthesis. A small amount goes into making bark. Wood itself is virtually pure cellulose, derived from air and water. If, when we farmed trees, we removed only the wood and left the leaves and bark on the site, we would be removing next to nothing from the soil. If the sawdust comes from a lumber mill, as opposed to a cabinet shop, it may also contain some bark and consequently small amounts of other essential nutrients.

Thoroughly moistened and heaped up, a sawdust pile would not heat up, only a few primary decomposers would take up residence. A person could wait five years for compost to form from pure moist sawdust and still not much would happen. Perhaps that’s why the words “compost” and “compote” as the British mean it, are connected. In England, a compote is a slightly fermented mixture of many things like fruits. If we mixed the sawdust with other materials having a very low C/N, then it would decompose, along with the other items.