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• expose more material to digestive enzymes;
  
  
• greatly accelerate decomposition;
  
  
• build much higher temperatures.

    Oxygen supply. All desirable organisms of decomposition are oxygen breathers or "aerobes. There must be an adequate movement 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 do not run by burning carbohydrates, but derive energy from other kinds of chemical reactions not requiring oxygen. Anaerobic chemistry is slow and does not generate much heat, so a pile that suddenly cools off is giving a strong indication that the core may lack air. The primary waste products of aerobes are water and carbon dioxide gas--inoffensive substances. When most people think of putrefaction they are actually picturing decomposition by anaerobic bacteria. With insufficient oxygen, foul-smelling materials are created. Instead of humus being formed, black, tarlike substances develop that are much less useful in soil. Under airless conditions much nitrate is permanently lost. The odiferous wastes of anaerobes also includes hydrogen sulfide (smells like rotten eggs), as well as other toxic substances with very unpleasant qualities.

    Heaps built with significant amounts of coarse, strong, irregular materials tend to retain large pore spaces, encourage airflow and remain aerobic. Heat generated in the pile causes hot air in the pile's center to rise and exit the pile by convection. This automatically draws in a supply of fresh, cool air. But heaps made exclusively of large particles not only present little surface area to microorganisms, they permit so much airflow that they are rapidly cooled. This is one reason that a wet firewood rick or a pile of damp wood chips 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 aerobic decomposition to a halt. In the center of an airless heap, anaerobic organisms immediately take over.

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

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

    Piles can also be constructed with a base layer of fine sticks, smaller tree prunings, and dry brushy material. This porous base tends to enhance the inflow of air from beneath the pile. One powerful aeration technique is to build the pile atop a low platform made of slats or strong hardware cloth.

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

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

    Since piles tend to compact and dry out 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, layer by layer. Two or three such turnings and waterings will result in finished compost.

    The other extreme can also be an obstacle to efficient composting. Making a pile too wet can encourage soft materials to lose all 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 nutrients that feed organisms of decomposition and later on, feed the garden itself. I cover my heaps with old plastic sheeting from November through March to protect them from Oregon's rainy winter climate.

    Understanding how much moisture to put into a pile soon becomes an intuitive certainty. Beginners can gauge moisture content by squeezing a handful of material very hard. It should feel very damp but only a few drops of moisture should be extractable. Industrial composters, who can afford scientific guidance to optimize their activities, try to establish and maintain a laboratory-measured moisture content of 50 to 60 percent by weight. When building a pile, keep in mind that certain materials like fresh grass clippings and vegetable trimmings already contain close to 90 percent moisture while dry components such as 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 will quickly equalize.

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

    However, even if you have unlimited material there is still a limit to the heap's size and that limiting factor is air supply. The bigger the compost pile the harder it becomes to get oxygen into the center. Industrial composters may have power equipment that simultaneously turns and sprays water, mechanically oxygenating and remoistening a massive windrow every few days. Even poorly-financed municipal composting systems have tractors with scoop loaders to turn their piles frequently. At home the practical limit is probably a heap six or seven feet wide at the base, initially about five feet high (it will rapidly slump a foot or so once heating begins), and as long as one has material for.

    Though we might like to make our compost piles 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 at once. A single lawn mowing doesn't supply that many clippings; my own kitchen compost bucket is larger and fills faster than anyone else's I know of but still only amounts to 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. So almost inevitably, you will be building a heap gradually.

    That's probably why most garden books illustrate 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 grass clippings, 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 compost pile this way because heating and decomposition begin before the pile is finished and it sags as it is built. I recommend several practices when gradually forming a heap.

    Keep a large stack of dry, coarse vegetation next to a building pile. As kitchen garbage, grass clippings, fresh manure or other wet 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 more nitrogen that balances out the higher carbon of dried grass, tall weeds, and hay.

    If building the heap has taken several months, the lower central area will probably be well on its way to becoming compost and much of the pile may have already dried out by the time it is fully formed. So the best time make the first turn and remoisten a long-building pile is right after it 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 and then kneaded and worked together so that the yeast can interact with the other materials and bring about a miraculous chemistry that we call dough.

    Carbon to nitrogen ratio. C/N is the most important single aspect that controls both the heap's ability to heat up and the quality of the compost that results. Piles composed primarily of materials with 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 nitrogen and may "burn out."

    The compost process generally works best when the heap's starting C/N is around 25:1. If sawdust, straw, or woody hay form the bulk of the pile, it is hard to bring the C/N down enough with just grass clippings and kitchen garbage. Heaps made essentially of high C/N materials need significant additions of the most potent manures and/or highly concentrated organic nitrogen sources like seed meals or slaughterhouse concentrates. The next chapter discusses the nature and properties of materials used for composting in great detail.

    I have already stressed that filling this book with tables listing so-called precise amounts of C/N for compostable materials would be foolish. Even more wasteful of energy would be the composter's attempt to compute 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 might be done.

    It is far more sensible to learn from experience. Gauge the proportions of materials going into a heap by the result. If the pile gets really hot and stays that way for a few weeks before gradually cooling down 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 too high. The words "thoroughly decomposed" mean here that there are no recognizable traces 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 provokes a marked growth response, similar to fertilizer.

    If the pile did not initially heat very 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 blending in more nutrient-rich materials and probably a bit of water too. After a few piles have been made novice composters will begin to get the same feel for their materials as bakers have for their flour, shortening, and yeast.

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

    There are other bacteria commonly found in soil that uptake ammonia gas and change it to the nitrates that plants and soil life forms need to make other proteins. These nitrification microorganisms are extremely efficient at reasonable temperatures but cannot survive the extreme high temperatures that a really hot pile can achieve. They also live only in soil. That is why it is very important to ensure that about 10 percent of a compost pile is soil and to coat the outside of a pile with a frosting of rich earth that is kept damp. One other aspect of soil helps prevent ammonia loss. Clay is capable of attracting and temporarily holding on to ammonia until it is nitrified by microorganisms. Most soils contain significant amounts of clay.

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

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

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

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

The Fertilizing Value of Compost

    It is not possible for me to tell you how well your own homemade compost will fertilize plants. Like home-brewed beer and home-baked bread you can be certain that your compost may be the equal of or superior to almost any commercially made product and certainly will be better fertilizer than the high carbon result of municipal solid waste composting. But first, let's consider two 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 organic matter to the soil, whether for lawns, ornamental plantings, or vegetable gardens. Compared to the fertilizer you would have purchased in its place, any homemade compost will be a financial gain unless you buy expensive motor-powered grinding equipment to produce only small quantities.

    Making compost is also a "personal good." For a few hours a year, composting gets you outside with a manure fork in 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 miraculous increase in plant and soil health that happens when you intensify and enrich that cycle of carbon on land under your control.

    So any compost is good compost. But will it be good fertilizer? Answering that question is a lot harder: it depends on so many factors. The growth response you'll get from compost depends on what went into 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 nitrogen was created by microbes during ripening.

    The growth response from compost also depends on the soil's temperature. Just like every other biological process, the nutrients in compost only GROW the plant when they decompose in the soil and are released. Where summer is hot, where the average of day and night temperatures are high, where soil temperatures reach 80° for much of the frost-free season, organic matter rots really fast and a little compost of average quality makes a huge increase in plant growth. Where summer is cool and soil organic matter decomposes slowly, poorer grades of compost have little immediate effect, or worse, may temporarily interfere with plant growth. Hotter soils are probably more desperate for organic matter 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 be stoked with more potent materials if high levels of nutrients are to be released.

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

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

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

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

    Perhaps you've noticed that I've still avoided answering the question, "how good is your compost?" First, lets take a look at laboratory analyses of various kinds of compost, connect that to what they 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 detailed breakdowns from more composting activities. But the data I do have is sufficient to appreciate the range of possibilities.

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

    Municipal composting schemes usually must process huge volumes of material on very valuable land close to cities. Economics mean the heaps are made as large as possible, run as fast as possible, and gotten off the field without concern for developing their highest qualities. Since it takes a long time to reduce large proportions of carbon, especially when they are in very decomposition-resistant forms like paper, and since the use of soil in the compost heap is essential to prevent nitrate loss, municipal composts tend to be low in nitrogen and high in carbon. By comparison, the poorest home garden compost I could find test results 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 went into either garden compost but my supposition is that gardener "A" incorporated large quantities of high C/N materials like straw, sawdust and the like while gardener "B" used manure, fresh vegetation, grass clippings and other similar low C/N materials. The next chapter will evaluate the suitability of materials commonly used to make compost.

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

    From many years of successful use I know that 15 to 20 sacks (about 300-400 dry-weight pounds) of 4-3-2 chicken compost spread and tilled into one thousand square feet will grow a magnificent garden. Most certainly a similar amount of the high analysis Garden "B" compost would do 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 municipal composting operation do as well? Not at all! Neither would three times as many sacks of dried steer manure. Here's why.

    If composted organic matter is spread like mulch atop the ground on lawns or around ornamentals and allowed to remain there its nitrogen content and C/N are not especially important. Even if the C/N is still high soil animals will continue the job of decomposition much as happens on the forest floor. 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 occur to the soil's process.

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

    But vegetables are delicate, pampered critters 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 nutrients as well as soft, friable soil containing reasonable levels of organic matter. So it is extremely important that a vegetable gardener understand the inevitable disruption occurring when organic matter that has a C/N is much above 12:1 is tilled into soil.

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

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

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

    During this period of rapid decomposition the 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 can be toxic to sprouting seeds and consequently, germination failures may occur. When I was in the seed business I'd get a few complaints every year from irate gardeners demanding to know why every seed packet they sowed failed to come up well. There were two usual causes. Either before sowing all the seeds were exposed to temperatures above 110° or more likely, a large quantity of high C/N "manure" was tilled into the garden just before sowing. In soil so disturbed transplants may also fail to grow for awhile. If the "manure" contains a large quantity of sawdust the soil will seem very infertile for a month or three.

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

    Rapid consumption of carbon continues until the C/N of the new material drops to the range of stable humus. Then decay microorganisms die off and the nutrients they hoarded are released back into the soil. How long the soil remains inhospitable to plant growth and seed germination depends 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 fertile the soil was before the addition of high C/N organic matter, the faster it will decompose.

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

    Yard waste compost is a product much like a homeowner would produce. And yard waste compost contains no industrial waste or any material that might pose health threats. All woody materials are finely chipped before composting and comprise no more than 20 percent of the total undecayed mass by weight. Although no nutrient analysis has been done by the county other than testing for 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/N of the materials going into the windrows at 25:1. I wouldn't be surprised if the finished compost has a C/N close to 12:1.

    Incidentally, Lane County understands that many gardeners don't have pickup trucks. They reasonably offer to deliver their compost for a small fee if at least one yard is purchased. Other local governments also 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 tilling your compost into soil seems to slow the growth of plants, then mulch with it and avoid tilling it in, or adjust the C/N down by adding fertilizers like seed meal when tilling it in.

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



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