HOME PAGE     SovereigntyLibrary    Go To Chapter Four




Organic Gardener's
Composting


by Steve Solomon






CHAPTER THREE

Practical Compost Making




    To make compost rot rapidly you needto achieve a strong and lasting rise in temperature. Cold piles will eventually decomposeand humus will eventually form but, without heat, the process can take a long, longtime. Getting a pile to heat up promptly and stay hot requires the right mixtureof materials and a sensible handling of the pile's air and moisture supply.

    Compost piles come with some built-inobstacles. The intense heat and biological activity make a heap slump into an airlessmass, yet if composting is to continue the pile must allow its living inhabitantssufficient air to breath. Hot piles tend to dry out rapidly, but must be kept moistor they stop working. But heat is desirable and watering cools a pile down. If understoodand managed, these difficulties are really quite minor.

    Composting is usually an inoffensiveactivity, but if done incorrectly there can be problems with odor and flies. Thischapter will show you how to make nuisance-free compost.


Hot Composting

    The main difference between compostingin heaps and natural decomposition on the earth's surface is temperature. On theforest floor, leaves leisurely decay and the primary agents of decomposition aresoil animals. Bacteria and other microorganisms are secondary. In a compost pilethe opposite occurs: we substitute a violent fermentation by microorganisms suchas bacteria and fungi. Soil animals are secondary and come into play only after themicrobes have had their hour.

    Under decent conditions, with a relativelyunlimited food supply, bacteria, yeasts, and fungi can double their numbers everytwenty to thirty minutes, increasing geometrically: 1, 2, 4, 8, 16, 32, 64, 128,256, 512, 1,024, 2,048, 4,096, etc. In only four hours one cell multiplies to overfour thousand. In three more hours there will be two million.

    For food, they consume the compostheap. Almost all oxygen-breathing organisms make energy by "burning" someform of organic matter as fuel much like gasoline powers an automobile. This cellularburning does not happen violently with flame and light. Living things use enzymesto break complex organic molecules down into simpler ones like sugar (and others)and then enzymatically unite these with oxygen. But as gentle as enzymatic combustionmay seem, it still is burning. Microbes can "burn" starches, cellulose,lignin, proteins, and fats, as well as sugars.

    No engine is one hundred percent efficient.All motors give off waste heat as they run. Similarly, no plant or animal is capableof using every bit of energy released from their food, and consequently radiate heat.When working hard, living things give off more heat; when resting, less. The ebband flow of heat production matches their oxygen consumption, and matches their physicaland metabolic activities, and growth rates. Even single-celled animals like bacteriaand fungi breathe oxygen and give off heat.

    Soil animals and microorganisms workingover the thin layer of leaf litter on the forest floor also generate heat but itdissipates without making any perceptible increase in temperature. However, compostablematerials do not transfer heat readily. In the language of architecture and homebuilding they might be said to have a high "R" value or to be good insulatorsWhen a large quantity of decomposing materials are heaped up, biological heat istrapped within the pile and temperature increases, further accelerating the rateof decomposition.

    Temperature controls how rapidly livingthings carry out their activities. Only birds and mammals are warm blooded-capableof holding the rate of their metabolic chemistry constant by holding their body temperaturesteady. Most animals and all microorganisms have no ability to regulate their internaltemperature; when they are cold they are sluggish, when warm, active. Driven by cold-bloodedsoil animals and microorganisms, the hotter the compost pile gets the faster it isconsumed.

    This relationship between temperatureand the speed of biological activity also holds true for organic chemical reactionsin a test-tube, the shelf-life of garden seed, the time it takes seed to germinateand the storage of food in the refrigerator. At the temperature of frozen water mostliving chemical processes come to a halt or close to it. That is why freezing preventsfood from going through those normal enzymatic decomposition stages we call spoiling.

    By the time that temperature has increasedto about 50° F, the chemistry of most living things is beginning to operateefficiently. From that temperature the speed of organic chemical reactions then approximatelydoubles with each 20 degree increase of temperature. So, at 70° F decompositionis running at twice the rate it does at 50°, while at 90° four times asrapidly as at 50° and so on. However, when temperatures get to about 150°organic chemistry is not necessarily racing 32 times as fast as compared to 50°because many reactions engendered by living things decline in efficiency at temperaturesmuch over 110°.

    This explanation is oversimplifiedand the numbers I have used to illustrate the process are slightly inaccurate, howeverthe idea itself is substantially correct. You should understand that while inorganicchemical reactions accelerate with increases in temperature almost without limit,those processes conducted by living things usually have a much lower terminal temperature.Above some point, life stops. Even the most heat tolerant soil animals will die orexit a compost pile by the time the temperature exceeds 120°, leaving the materialin the sole possession of microorganisms.

    Most microorganisms cannot withstandtemperatures much over 130°. When the core of a pile heats beyond this pointthey either form spores while waiting for things to cool off, or die off. Plentyof living organisms will still be waiting in the cooler outer layers of the heapto reoccupy the core once things cool down. However, there are unique bacteria andfungi that only work effectively at temperatures exceeding 110°. Soil scientistsand other academics that sometimes seem to measure their stature on how well theycan baffle the average person by using unfamiliar words for ordinary notions callthese types of organisms thermophiles, a Latin word that simply means "heatlovers."

    Compost piles can get remarkably hot.Since thermophilic microorganisms and fungi generate the very heat they require toaccelerate their activities and as the ambient temperature increases generate evenmore heat, the ultimate temperature is reached when the pile gets so hot that eventhermophilic organisms begin to die off. Compost piles have exceeded 160°. Youshould expect the heaps you build to exceed 140° and shouldn't be surprisedif they approach 150°

    Other types of decomposing organicmatter can get even hotter. For example, haystacks commonly catch on fire becausedry hay is such an excellent insulator. If the bales in the center of a large haystack are just moist enough to encourage rapid bacterial decomposition, the heatgenerated may increase until dryer bales on the outside begin to smoke and then burn.Wise farmers make sure their hay is thoroughly dry before baling and stacking it.

    How hot the pile can get depends onhow well the composter controls a number of factors. These are so important thatthey need to be considered in detail.

    Particle size. Microorganismsare not capable of chewing or mechanically attacking food. Their primary method ofeating is to secrete digestive enzymes that break down and then dissolve organicmatter. Some larger single-cell creatures can surround or envelop and then "swallow"tiny food particles. Once inside the cell this material is then attacked by similardigestive enzymes.

    Since digestive enzymes attack onlyoutside surfaces, the greater the surface area the composting materials present themore rapidly microorganisms multiply to consume the food supply. And the more heatis created. As particle size decreases, the amount of surface area goes up just aboutas rapidly as the number series used a few paragraphs back to illustrate the multiplicationof microorganisms.

    The surfaces presented in differenttypes of soil similarly affect plant growth so scientists have carefully calculatedthe amount of surface areas of soil materials. Although compost heaps are made ofmuch larger particles than soil, the relationship between particle size and surfacearea is the same. Clearly, when a small difference in particle size can change theamount of surface area by hundreds of times, reducing the size of the stuff in thecompost pile will:

    Oxygen supply. All desirable organismsof decomposition are oxygen breathers or "aerobes. There must be an adequatemovement of air through the pile to supply their needs. If air supply is choked off,aerobic microorganisms die off and are replaced by anaerobic organisms. These donot run by burning carbohydrates, but derive energy from other kinds of chemicalreactions not requiring oxygen. Anaerobic chemistry is slow and does not generatemuch heat, so a pile that suddenly cools off is giving a strong indication that thecore may lack air. The primary waste products of aerobes are water and carbon dioxidegas--inoffensive substances. When most people think of putrefaction they are actuallypicturing decomposition by anaerobic bacteria. With insufficient oxygen, foul-smellingmaterials are created. Instead of humus being formed, black, tarlike substances developthat are much less useful in soil. Under airless conditions much nitrate is permanentlylost. The odiferous wastes of anaerobes also includes hydrogen sulfide (smells likerotten eggs), as well as other toxic substances with very unpleasant qualities.

    Heaps built with significant amountsof coarse, strong, irregular materials tend to retain large pore spaces, encourageairflow and remain aerobic. Heat generated in the pile causes hot air in the pile'scenter to rise and exit the pile by convection. This automatically draws in a supplyof fresh, cool air. But heaps made exclusively of large particles not only presentlittle surface area to microorganisms, they permit so much airflow that they arerapidly cooled. This is one reason that a wet firewood rick or a pile of damp woodchips does not heat up. At the opposite extreme, piles made of finely ground or soft,wet materials tend to compact, ending convective air exchanges and bringing aerobicdecomposition to a halt. In the center of an airless heap, anaerobic organisms immediatelytake over.

Surface Area of One Gram of Soil Particles
Particle Size Diameter of Particles in mm Number of Particles per gm Surface Area per square cm
       
Very Coarse Sand 2.00-1.00 90 11
Coarse Sand 1.00-0.50 720 23
Medium Sand 0.50-0.25 5,700 45
Find Sand 0.25-0.10 46,000 91
Very Fine Sand 0.10-005 772,000 227
Silt 0.05-0.002 5,776,000 454



    Composters use several strategies tomaintain airflow. The most basic one is to blend an assortment of components so thatcoarse, stiff materials maintain a loose texture while soft, flexible stuff tendsto partially fill in the spaces. However, even if the heap starts out fluffy enoughto permit adequate airflow, as the materials decompose they soften and tend to slumptogether into an airless mass.

    Periodically turning the pile, tearingit apart with a fork and restacking it, will reestablish a looser texture and temporarilyrecharge the pore spaces with fresh air. Since the outer surfaces of a compost piledo not get hot, tend to completely dry out, and fail to decompose, turning the pilealso rotates the unrotted skin to the core and then insulates it with more-decomposedmaterial taken from the center of the original pile. A heap that has cooled becauseit has gone anaerobic can be quickly remedied by turning.

    Piles can also be constructed witha base layer of fine sticks, smaller tree prunings, and dry brushy material. Thisporous base tends to enhance the inflow of air from beneath the pile. One powerfulaeration technique is to build the pile atop a low platform made of slats or stronghardware cloth.

    Larger piles can have air channelsbuilt into them much as light wells and courtyards illuminate inner rooms of tallbuildings. As the pile is being constructed, vertical heavy wooden fence posts, 4x 4's, or large-diameter plastic pipes with numerous quarter-inch holes drilled inthem are spaced every three or four feet. Once the pile has been formed and beginsto heat, the wooden posts are wiggled around and then lifted out, making a slightlyconical airway from top to bottom. Perforated plastic vent pipes can be left in theheap. With the help of these airways, no part of the pile is more than a couple offeet from oxygen

    Moisture. A dry pile is a coldpile. Microorganisms live in thin films of water that adhere to organic matter whereasfungi only grow in humid conditions; if the pile becomes dry, both bacteria and fungidie off. The upwelling of heated air exiting the pile tends to rapidly dehydratethe compost heap. It usually is necessary to periodically add water to a hot workingheap. Unfortunately, remoistening a pile is not always simple. The nature of thematerials tends to cause water to be shed and run off much like a thatched roof protectsa cottage.

    Since piles tend to compact and dryout at the same time, when they are turned they can simultaneously be rehydrated.When I fork over a heap I take brief breaks and spray water over the new pile, layerby layer. Two or three such turnings and waterings will result in finished compost.

    The other extreme can also be an obstacleto efficient composting. Making a pile too wet can encourage soft materials to loseall mechanical strength, the pile immediately slumps into a chilled, airless mass.Having large quantities of water pass through a pile can also leach out vital nutrientsthat feed organisms of decomposition and later on, feed the garden itself. I covermy heaps with old plastic sheeting from November through March to protect them fromOregon's rainy winter climate.

    Understanding how much moisture toput into a pile soon becomes an intuitive certainty. Beginners can gauge moisturecontent by squeezing a handful of material very hard. It should feel very damp butonly a few drops of moisture should be extractable. Industrial composters, who canafford scientific guidance to optimize their activities, try to establish and maintaina laboratory-measured moisture content of 50 to 60 percent by weight. When buildinga pile, keep in mind that certain materials like fresh grass clippings and vegetabletrimmings already contain close to 90 percent moisture while dry components suchas sawdust and straw may contain only 10 percent and resist absorbing water at that.But, by thoroughly mixing wet and dry materials the overall moisture content willquickly equalize.

    Size of the pile. It is muchharder to keep a small object hot than a large one. That's because the ratio of surfacearea to volume goes down as volume goes up. No matter how well other factors encouragethermophiles, it is still difficult to make a pile heat up that is less than threefeet high and three feet in diameter. And a tiny pile like that one tends to heatonly for a short time and then cool off rapidly. Larger piles tend to heat much fasterand remain hot long enough to allow significant decomposition to occur. Most compostersconsider a four foot cube to be a minimum practical size. Industrial or municipalcomposters build windrows up to ten feet at the base, seven feet high, and as longas they want.

    However, even if you have unlimitedmaterial there is still a limit to the heap's size and that limiting factor is airsupply. The bigger the compost pile the harder it becomes to get oxygen into thecenter. Industrial composters may have power equipment that simultaneously turnsand sprays water, mechanically oxygenating and remoistening a massive windrow everyfew days. Even poorly-financed municipal composting systems have tractors with scooploaders to turn their piles frequently. At home the practical limit is probably aheap six or seven feet wide at the base, initially about five feet high (it willrapidly slump a foot or so once heating begins), and as long as one has materialfor.

    Though we might like to make our compostpiles so large that maintaining sufficient airflow becomes the major problem we face,the home composter rarely has enough materials on hand to build a huge heap all atonce. A single lawn mowing doesn't supply that many clippings; my own kitchen compostbucket is larger and fills faster than anyone else's I know of but still only amountsto a few gallons a week except during August when we're making jam, canning vegetables,and juicing. Garden weeds are collected a wheelbarrow at a time. Leaves are seasonal.In the East the annual vegetable garden clean-up happens after the fall frost. Soalmost inevitably, you will be building a heap gradually.

    That's probably why most garden booksillustrate compost heaps as though they were layer cakes: a base layer of brush,twigs, and coarse stuff to allow air to enter, then alternating thin layers of grassclippings, leaves, weeds, garbage, grass, weeds, garbage, and a sprinkling of soil,repeated until the heap is five feet tall. It can take months to build a compostpile this way because heating and decomposition begin before the pile is finishedand it sags as it is built. I recommend several practices when gradually forminga heap.

    Keep a large stack of dry, coarse vegetationnext to a building pile. As kitchen garbage, grass clippings, fresh manure or otherwet materials come available the can be covered with and mixed into this dry material.The wetter, greener items will rehydrate the dry vegetation and usually contain morenitrogen that balances out the higher carbon of dried grass, tall weeds, and hay.

    If building the heap has taken severalmonths, the lower central area will probably be well on its way to becoming compostand much of the pile may have already dried out by the time it is fully formed. Sothe best time make the first turn and remoisten a long-building pile is right afterit has been completed.

    Instead of picturing a layer cake,you will be better off comparing composting to making bread. Flour, yeast, water,molasses, sunflower seeds, and oil aren't layered, they're thoroughly blended andthen kneaded and worked together so that the yeast can interact with the other materialsand bring about a miraculous chemistry that we call dough.

    Carbon to nitrogen ratio. C/Nis the most important single aspect that controls both the heap's ability to heatup and the quality of the compost that results. Piles composed primarily of materialswith a high ratio of carbon to nitrogen do not get very hot or stay hot long enough.Piles made from materials with too low a C/N get too hot, lose a great deal of nitrogenand may "burn out."

    The compost process generally worksbest when the heap's starting C/N is around 25:1. If sawdust, straw, or woody hayform the bulk of the pile, it is hard to bring the C/N down enough with just grassclippings and kitchen garbage. Heaps made essentially of high C/N materials needsignificant additions of the most potent manures and/or highly concentrated organicnitrogen sources like seed meals or slaughterhouse concentrates. The next chapterdiscusses the nature and properties of materials used for composting in great detail.

    I have already stressed that fillingthis book with tables listing so-called precise amounts of C/N for compostable materialswould be foolish. Even more wasteful of energy would be the composter's attempt tocompute the ratio of carbon to nitrogen resulting from any mixture of materials.For those who are interested, the sidebar provides an illustration of how that mightbe done.



Balancing C/N


    Here's a simple arithmetic problem that illustrates how to balance carbon to nitrogen.

QUESTION: I have 100 pounds of straw with a C/N of 66:1, how much chicken manure (C/N of 8:1) do I have to add to bring the total to an average C/N of 25:1.

ANSWER: There is 1 pound of nitrogen already in each 66 pounds of straw, so there are already about 1.5 pounds of N in 100 pounds of straw. 100 pounds of straw-compost at 25:1 would have about 4 pounds of nitrogen, so I need to add about 2.5 more pounds of N. Eight pounds of chicken manure contain 1 pound of N; 16 pounds have 2. So, if I add 32 pounds of chicken manure to 100 pounds of straw, I will have 132 pounds of material containing about 5.5 pounds of N, a C/N of 132:5.5 or about 24:1.


    It is far more sensible to learn fromexperience. Gauge the proportions of materials going into a heap by the result. Ifthe pile gets really hot and stays that way for a few weeks before gradually coolingdown then the C/N was more or less right. If, after several turnings and reheatings,the material has not thoroughly decomposed, then the initial C/N was probably toohigh. The words "thoroughly decomposed" mean here that there are no recognizabletraces of the original materials in the heap and the compost is dark brown to black,crumbly, sweet smelling and most importantly, when worked into soil it provokesa marked growth response, similar to fertilizer.

    If the pile did not initially heatvery much or the heating stage was very brief, then the pile probably lacked nitrogen.The solution for a nitrogen-deficient pile is to turn it, simultaneously blendingin more nutrient-rich materials and probably a bit of water too. After a few pileshave been made novice composters will begin to get the same feel for their materialsas bakers have for their flour, shortening, and yeast.

    It is also possible to err on the oppositeend of the scale and make a pile with too much nitrogen. This heap will heat veryrapidly, become as hot as the microbial population can tolerate, lose moisture veryquickly, and probably smell of ammonia, indicating that valuable fixed nitrogen isescaping into the atmosphere. When proteins decompose their nitrogen content is normallyreleased as ammonia gas. Most people have smelled small piles of spring grass clippingsdoing this very thing. Ammonia is always created when proteins decompose in any heapat any C/N. But a properly made compost pile does not permit this valuable nitrogensource to escape.

    There are other bacteria commonly foundin soil that uptake ammonia gas and change it to the nitrates that plants and soillife forms need to make other proteins. These nitrification microorganisms are extremelyefficient at reasonable temperatures but cannot survive the extreme high temperaturesthat a really hot pile can achieve. They also live only in soil. That is why it isvery important to ensure that about 10 percent of a compost pile is soil and to coatthe outside of a pile with a frosting of rich earth that is kept damp. One otheraspect of soil helps prevent ammonia loss. Clay is capable of attracting and temporarilyholding on to ammonia until it is nitrified by microorganisms. Most soils containsignificant amounts of clay.

    The widespread presence of clay andammonia-fixing bacteria in all soils permits industrial farmers to inject gaseousammonia directly into the earth where it is promptly and completely altered intonitrates. A very hot pile leaking ammonia may contain too little soil, but more likelyit is also so hot that the nitrifying bacteria have been killed off. Escaping ammoniais not only an offensive nuisance, valuable fertility is being lost into the atmosphere.

    Weather and season. You canadopt a number of strategies to keep weather from chilling a compost pile. Wind bothlowers temperature and dries out a pile, so if at all possible, make compost in asheltered location. Heavy, cold rains can chill and waterlog a pile. Composting undera roof will also keep hot sun from baking moisture out of a pile in summer. Usingbins or other compost structures can hold in heat that might otherwise be lost fromthe sides of unprotected heaps.

    It is much easier to maintain a highcore temperature when the weather is warm. It may not be so easy to make hot compostheaps during a northern winter. So in some parts of the country I would not expecttoo much from a compost pile made from autumn cleanup. This stack of leaves and frost-bittengarden plants may have to await the spring thaw, then to be mixed with potent springgrass clippings and other nitrogenous materials in order to heat up and completethe composting process. What to do with kitchen garbage during winter in the frozenNorth makes an interesting problem and leads serious recyclers to take notice ofvermicomposting. (See Chapter 6.)

    In southern regions the heap may beprevented from overheating by making it smaller or not as tall. Chapter Nine describesin great detail how Sir Albert Howard handled the problem of high air temperaturewhile making compost in India.



The Fertilizing Value of Compost

    It is not possible for me to tell youhow well your own homemade compost will fertilize plants. Like home-brewed beer andhome-baked bread you can be certain that your compost may be the equal of or superiorto almost any commercially made product and certainly will be better fertilizer thanthe high carbon result of municipal solid waste composting. But first, let's considertwo semi-philosophical questions, "good for what?" and "poor as what?"

    Any compost is a "social good"if it conserves energy, saves space in landfills and returns some nutrients and organicmatter to the soil, whether for lawns, ornamental plantings, or vegetable gardens.Compared to the fertilizer you would have purchased in its place, any homemade compostwill be a financial gain unless you buy expensive motor-powered grinding equipmentto produce only small quantities.

    Making compost is also a "personalgood." For a few hours a year, composting gets you outside with a manure forkin your hand, working up a sweat. You intentionally participate in a natural cycle:the endless rotation of carbon from air to organic matter in the form of plants,to animals, and finally all of it back into soil. You can observe the miraculousincrease in plant and soil health that happens when you intensify and enrich thatcycle of carbon on land under your control.

    So any compost is good compost. Butwill it be good fertilizer? Answering that question is a lot harder: it depends onso many factors. The growth response you'll get from compost depends on what wentinto the heap, on how much nitrate nitrogen was lost as ammonia during decomposition,on how completely decomposition was allowed to proceed, and how much nitrate nitrogenwas created by microbes during ripening.

    The growth response from compost alsodepends on the soil's temperature. Just like every other biological process, thenutrients in compost only GROW the plant when they decompose in the soil and arereleased. Where summer is hot, where the average of day and night temperatures arehigh, where soil temperatures reach 80° for much of the frost-free season, organicmatter rots really fast and a little compost of average quality makes a huge increasein plant growth. Where summer is cool and soil organic matter decomposes slowly,poorer grades of compost have little immediate effect, or worse, may temporarilyinterfere with plant growth. Hotter soils are probably more desperate for organicmatter and may give you a marked growth response from even poor quality compost;soils in cool climates naturally contain higher quantities of humus and need to bestoked with more potent materials if high levels of nutrients are to be released.

    Compost is also reputed to make enormousimprovements in the workability, or tilth of the soil. This aspect of gardening isso important and so widely misunderstood, especially by organic gardeners, that mostof Chapter Seven is devoted to considering the roles of humus in the soil.



GROWing the plant


    One of the things I enjoy most while gardening is GROWing some of my plants. I don't GROW them all because there is no point in having giant parsley or making the corn patch get one foot taller. Making everything get as large as possible wouldn't result in maximum nutrition either. But just for fun, how about a 100-plus-pound pumpkin? A twenty-pound savoy cabbage? A cauliflower sixteen inches in diameter? An eight-inch diameter beet? Now that's GROWing!

    Here's how. Simply remove as many growth limiters as possible and watch the plant's own efforts take over. One of the best examples I've ever seen of how this works was in a neighbor's backyard greenhouse. This retired welder liked his liquor. Having more time than money and little respect for legal absurdities, he had constructed a small stainless steel pot still, fermented his own mash, and made a harsh, hangover-producing whiskey from grain and cane sugar that Appalachians call "popskull." To encourage rapid fermentation, his mashing barrel was kept in the warm greenhouse. The bubbling brew gave off large quantities of carbon dioxide gas.

    The rest of his greenhouse was filled with green herbs that flowered fragrantly in September. Most of them were four or five feet tall but those plants on the end housing the mash barrel were seven feet tall and twice as bushy. Why? Because the normal level of atmospheric CO2 actually limits plant growth.

    We can't increase the carbon supply outdoors. But we can loosen the soil eighteen to twenty-four inches down (or more for deeply-rooting species) in an area as large as the plant's root system could possibly ramify during its entire growing season. I've seen some GROWers dig holes four feet deep and five feet in diameter for individual plants. We can use well-finished, strong compost to increase the humus content of that soil, and supplement that with manure tea or liquid fertilizer to provide all the nutrients the plant could possibly use. We can allocate only one plant to that space and make sure absolutely no competition develops in that space for light, water, or nutrients. We can keep the soil moist at all times. By locating the plant against a reflective white wall we can increase its light levels and perhaps the nighttime temperatures (plants make food during the day and use it to grow with at night).



    Textural improvements from compostdepend greatly on soil type. Sandy and loamy soils naturally remain open and workableand sustain good tilth with surprisingly small amounts of organic matter. Two orthree hundred pounds (dry weight) of compost per thousand square feet per year willkeep coarse-textured soils in wonderful physical condition. This small amount ofhumus is also sufficient to encourage the development of a lush soil ecology thatcreates the natural health of plants.

    Silty soils, especially ones with moreclay content, tend to become compacted and when low in humus will crust over andpuddle when it rains hard. These may need a little more compost, perhaps in the rangeof three to five hundred pounds per thousand square feet per year.

    Clay soils on the other hand are heavyand airless, easily compacted, hard to work, and hard to keep workable. The mechanicalproperties of clay soils greatly benefit from additions of organic matter severaltimes larger than what soils composed of larger particles need. Given adequate organicmatter, even a heavy clay can be made to behave somewhat like a rich loam does.

    Perhaps you've noticed that I've stillavoided answering the question, "how good is your compost?" First, letstake a look at laboratory analyses of various kinds of compost, connect that to whatthey were made from and that to the kind of growing results one might get from them.I apologize that despite considerable research I was unable to discover more detailedbreakdowns from more composting activities. But the data I do have is sufficientto appreciate the range of possibilities.

    Considered as a fertilizer to GROWplants, Municipal Solid Waste (MSW) compost is the lowest grade material I know of.It is usually broadcast as a surface mulch. The ingredients municipal compostersmust process include an indiscriminate mixture of all sorts of urban organic waste:paper, kitchen garbage, leaves, chipped tree trimmings, commercial organic garbagelike restaurant waste, cannery wastes, etc. Unfortunately, paper comprises the largestsingle ingredient and it is by nature highly resistant to decomposition. MSW compostingis essentially a recycling process, so no soil, no manure and no special low C/Nsources are used to improve the fertilizing value of the finished product.

    Municipal composting schemes usuallymust process huge volumes of material on very valuable land close to cities. Economicsmean the heaps are made as large as possible, run as fast as possible, and gottenoff the field without concern for developing their highest qualities. Since it takesa long time to reduce large proportions of carbon, especially when they are in verydecomposition-resistant forms like paper, and since the use of soil in the compostheap is essential to prevent nitrate loss, municipal composts tend to be low in nitrogenand high in carbon. By comparison, the poorest home garden compost I could find testresults for was about equal to the best municipal compost. The best garden sample("B") is pretty fine stuff. I could not discover the ingredients that wentinto either garden compost but my supposition is that gardener "A" incorporatedlarge quantities of high C/N materials like straw, sawdust and the like while gardener"B" used manure, fresh vegetation, grass clippings and other similar lowC/N materials. The next chapter will evaluate the suitability of materials commonlyused to make compost.

Analyses of Various Composts
Source N% P% K% Ca% C/N
Vegetable trimmings & paper 1.57 0.40 0.40   24:1
Municipal refuse 0.97 0.16 0.21   24:1
Johnson City refuse 0.91 0.22 0.91 1.91 36:1
Gainsville, FL refuse 0.57 0.26 0.22 1.88 ?
Garden compost "A" 1.40 0.30 0.40   25:1
Garden compost "B" 3.50 1.00 2.00   10:1



    To interpret this chart, let's makeas our standard of comparison the actual gardening results from some very potentorganic material I and probably many of my readers have probably used: bagged chickenmanure compost. The most potent I've ever purchased is inexpensively sold in one-cubic-footplastic sacks stacked up in front of my local supermarket every spring. The sacksare labeled 4-3-2. I've successfully grown quite a few huge, handsome, and healthyvegetables with this product. I've also tried other similar sorts also labeled "chickenmanure compost" that are about half as potent.

    From many years of successful use Iknow that 15 to 20 sacks (about 300-400 dry-weight pounds) of 4-3-2 chicken compostspread and tilled into one thousand square feet will grow a magnificent garden. Mostcertainly a similar amount of the high analysis Garden "B" compost woulddo about the same job. Would three times as much less potent compost from Garden"A" or five times as much even poorer stuff from the Johnson City municipalcomposting operation do as well? Not at all! Neither would three times as many sacksof dried steer manure. Here's why.

    If composted organic matter is spreadlike mulch atop the ground on lawns or around ornamentals and allowed to remain thereits nitrogen content and C/N are not especially important. Even if the C/N is stillhigh soil animals will continue the job of decomposition much as happens on the forestfloor. Eventually their excrement will be transported into the soil by earthworms.By that time the C/N will equal that of other soil humus and no disruption will occurto the soil's process.

    Growing vegetables is much more demandingthan growing most perennial ornamentals or lawns. Excuse me, flower gardeners, butI've observed that even most flowers will thrive if only slight improvements aremade in their soil. The same is true for most herbs. Difficulties with ornamentalsor herbs are usually caused by attempting to grow a species that is not particularlywell-adapted to the site or climate. Fertilized with sacked steer manure or mulchedwith average-to-poor compost, most ornamentals will grow adequately.

    But vegetables are delicate, pamperedcritters that must grow as rapidly as they can grow if they are to be succulent,tasty, and yield heavily. Most of them demand very high levels of available nutrientsas well as soft, friable soil containing reasonable levels of organic matter. Soit is extremely important that a vegetable gardener understand the inevitable disruptionoccurring when organic matter that has a C/N is much above 12:1 is tilled into soil.

    Organic matter that has been in soilfor a while has been altered into a much studied substance, humus. We know for examplethat humus always has a carbon to nitrogen ratio of from 10:1 to about 12:1, justlike compost from Garden "B." Garden writers call great compost like this,"stable humus," because it is slow to decompose. Its presence in soil steadilyfeeds a healthy ecology of microorganisms important to plant health, and whose activityaccelerates release of plant nutrients from undecomposed rock particles. Humus isalso fertilizer because its gradual decomposition provides mineral nutrients thatmake plants grow. The most important of these nutrients is nitrate nitrogen, thussoil scientists may call humus decomposition "nitrification."

    When organic material with a C/N below12:1 is mixed into soil its breakdown is very rapid. Because it contains more nitrogenthan stable humus does, nitrogen is rapidly released to feed the plants and soillife. Along with nitrogen comes other plant nutrients. This accelerated nitrificationcontinues until the remaining nitrogen balances with the remaining carbon at a ratioof about 12:1. Then the soil returns to equilibrium. The lower the C/N the more rapidthe release, and the more violent the reaction in the soil. Most low C/N organicmaterials, like seed meal or chicken manure, rapidly release nutrients for a monthor two before stabilizing. What has been described here is fertilizer.

    When organic material with a C/N higherthan 12:1 is tilled into soil, soil animals and microorganisms find themselves withan unsurpassed carbohydrate banquet. Just as in a compost heap, within days bacteriaand fungi can multiply to match any food supply. But to construct their bodies thesemicroorganisms need the same nutrients that plants need to grow--nitrogen, potassium,phosphorus, calcium, magnesium, etc. There are never enough of these nutrients inhigh C/N organic matter to match the needs of soil bacteria, especially never enoughnitrogen, so soil microorganisms uptake these nutrients from the soil's reserveswhile they "bloom" and rapidly consume all the new carbon presented tothem.


    During this period of rapid decompositionthe soil is thoroughly robbed of plant nutrients. And nitrification stops. Initially,a great deal of carbon dioxide gas may be given off, as carbon is metabolically "burned."However, CO2 in high concentrations canbe toxic to sprouting seeds and consequently, germination failures may occur. WhenI was in the seed business I'd get a few complaints every year from irate gardenersdemanding to know why every seed packet they sowed failed to come up well. Therewere two usual causes. Either before sowing all the seeds were exposed to temperaturesabove 110° or more likely, a large quantity of high C/N "manure" wastilled into the garden just before sowing. In soil so disturbed transplants may alsofail to grow for awhile. If the "manure" contains a large quantity of sawdustthe soil will seem very infertile for a month or three.

    Sir Albert Howard had a unique andpithy way of expressing this reality. He said that soil was not capable of workingtwo jobs at once. You could not expect it to nitrify humus while it was also beingrequired to digest organic matter. That's one reason he thought composting was sucha valuable process. The digestion of organic matter proceeds outside the soil; whenfinished product, humus, is ready for nitrification, it is tilled in.

    Rapid consumption of carbon continuesuntil the C/N of the new material drops to the range of stable humus. Then decaymicroorganisms die off and the nutrients they hoarded are released back into thesoil. How long the soil remains inhospitable to plant growth and seed germinationdepends on soil temperature, the amount of the material and how high its C/N is,and the amount of nutrients the soil is holding in reserve. The warmer and more fertilethe soil was before the addition of high C/N organic matter, the faster it will decompose.

    Judging by the compost analyses inthe table, I can see why some municipalities are having difficulty disposing of thesolid waste compost they are making. One governmental composting operation that doessucceed in selling everything they can produce is Lane County, Oregon. Their yardwaste compost is eagerly paid for by local gardeners. Lane County compost ismade only from autumn leaves, grass clippings, and other yard wastes. No paper!

    Yard waste compost is a product muchlike a homeowner would produce. And yard waste compost contains no industrial wasteor any material that might pose health threats. All woody materials are finely chippedbefore composting and comprise no more than 20 percent of the total undecayed massby weight. Although no nutrient analysis has been done by the county other than testingfor pH (around 7.0) and, because of the use of weed and feed fertilizers on lawns,for 2-4D (no residual trace ever found present), I estimate that the overall C/Nof the materials going into the windrows at 25:1. I wouldn't be surprised if thefinished compost has a C/N close to 12:1.

    Incidentally, Lane County understandsthat many gardeners don't have pickup trucks. They reasonably offer to deliver theircompost for a small fee if at least one yard is purchased. Other local governmentsalso make and deliver yard waste compost.

    So what about your own home compost?If you are a flower, ornamental, or lawn grower, you have nothing to worry about.Just compost everything you have available and use all you wish to make. If tillingyour compost into soil seems to slow the growth of plants, then mulch with it andavoid tilling it in, or adjust the C/N down by adding fertilizers like seed mealwhen tilling it in.

    If you are a vegetable gardener andyour compost doesn't seem to provoke the kind of growth response you hoped for, eithershallowly till in compost in the fall for next year's planting, by which time itwill have become stable humus, or read further. The second half of this book containsnumerous hints about how to make potent compost and about how to use complete organicfertilizers in combination with compost to grow the lushest garden imaginable.



HOME PAGE     SovereigntyLibrary    Go To Chapter Four