Compost (Guide to Backyard Farming)

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Anytime you pass by a forest or a long-abandoned field, you see tons of vegetation even though it is pretty obvious nobody is fertilizing the wilderness. Forests and fields don't need fertilizer , because they exist within the framework of a sustainable nutrient cycle that returns nutrients to the soil via natural composting.

A tree takes elements from the earth and turns them into leaves that turn brown and fall to earth in the autumn, forming a layer on top of last year's leaves. Progressing down the layers, within just a few inches, the leaves have turned into a sweet-smelling, living compost. This gets mixed into the existing soil through the action of earthworms and other organisms. The same mechanism is at work when a squirrel eats an acorn and drops the shell to the forest floor and then relieves himself. It all combines in the forest floor so that everything goes back whence it came and becomes available for reuse.

This same is true even in death. The squirrel eaten by a hawk has all of its parts, in some form or another , returned to the earth;

likewise, a huge tree hit by lightning decomposes into the earth for reuse.

Nature is already equipped to sustain itself, as it has for billions of years. Taking energy only from the sun, nature follows the Law of Conservation of Matter to recycle all of the elements that it takes from the earth. This cycle does not work within a given area of land when elements are removed from that area more quickly than they can be replaced without taking elements from somewhere else.

This is where conventional farming cartels find themselves. They export all of their fertility from their farms in the form of crops and then replenish that fertility with artificial chemicals or with manures brought in from several states away. Such a system can endure for a long time, but it is pretty expensive and geared best to large-scale operations. Smaller-scale home-sized operations work least expensively when every effort is made to maintain as much soil fertility as possible from sources within the operation. Conscientious attention to the nutrient cycles of the mini-farm can make a huge difference in crop yield and the amount of outside amendments and fertilizers that must be brought in-which in practical terms means reduced costs.

The nutrient cycles of the mini-farm encompass the life-death rebirth of plants and animals as well as the grow-eat-excrete-grow of the plants and animals on the farm. The mini-farmer uses composting and fertilizer crops to accelerate the natural process of these cycles to maintain a high level of fertility in the soil.

The importance of compost in a mini-farm or even a small garden can't be overstated. Broadly, compost is the rotted remains of plant and animal products and by-products that have been aerobically decomposed so that the individual constituents cannot be distinguished. This is exactly what happens in nature, and the mini farmer simply helps the process along. Once this has occurred, the resulting product becomes agriculturally indispensable.

Compost not only serves as a reservoir of fertility because of the individual elements and nutrients that it contains but also serves to destroy plant and animal diseases and toxins while improving the texture and moisture handling of the soil to which it is added. One commercial California vegetable grower was able to reduce pesticide use by 80% in just three years through applications of compost.

The Composting Process

The core process of composting is simply this: The farmer stacks up a bunch of organic matter that, given time, air , and moisture, decomposes. Organic matter includes leftovers from the table, crop debris, grass clippings, leaves raked in the fall, and animal manure.

In essence, anything that was either once alive or produced by something that was alive.

A combination of elements are responsible for organic decomposition but most notably microorganisms such as bacteria and fungi that are already present in soil, on plants, and even in the intestines of animals. When an environment hospitable to their growth and multiplication is created, the microorganisms digest the organic material. Along with this, a number of larger organisms such as earthworms get into the act of digesting the organic matter, thus creating an entirely different substance than what existed in the first place.

Microorganisms, like people, have different dietary and climate preferences. Some prefer to eat leaves, some prefer to eat straw, and others prefer to eat apples. As a result, the best level of decomposition and fertility occurs from adding a variety of organic substances to the pile.

Microorganisms are likewise competitive. Every species (and even variant of a given species) wants to make room for itself and its offspring. Because of this, many microorganisms have developed a variety of weapons that can be used against other microbes in the compost pile. The most widely understood is the production of antibiotics by a variety of organisms intended to inhibit the growth of other organisms. Heat-loving bacteria in a compost pile endeavor to heat up the pile to a high-enough temperature that other bacteria can't tolerate the heat and die off. But once they've finished their job, mesophilic bacteria move back into the pile and take over again, along with fungi and finally earthworms.

Composting to Destroy Pathogens

The microorganisms that create compost can be broadly classified as being either thermophilic-meaning "heat loving"-or mesophilic-meaning "intermediate loving"-both terms referring to the temperatures preferred and created by such microorganisms. A compost pile is called either thermophilic or mesophilic depending on the temperatures it achieves.

The most important aspect of the relative heat of a compost pile is pathogen death. Thermophilic composting will kill all known human pathogens-including parasitic worm eggs, bacteria, viruses, and protozoa-along with plant disease organisms and weed seeds.

Using thermophilic composting, it is both possible and practical to recycle not just ordinary plant material such as leaves and grass clippings but also leftover fried chicken. In other words, thermophilic composting makes a much broader array of compost ingredients both practical and safe.

There are two factors affecting the death of plant or animal pathogens and weed seeds in compost. The temperature achieved by the compost, as mentioned, is a big factor . Another important factor is the time that the compost is held before being used.

Microbial pathogens require particular hosts to complete their life cycles, and their spores can remain inert-and thus viable-only in a warm, moist compost pile for so long. Even if a compost pile isn't thermophilic, adequate holding time will still render the compost both safe and beneficial. Weed seeds can be killed by the high heat of a thermophilic compost pile, but they can also be killed by virtue of the fact that the warmth of even a mesophilic pile can induce premature germination, thus interrupting the life cycle of the weeds.

The holding time for mesophilic compost is two years if it contains, or is likely to contain, pathogens from infected crops, dead animals, or other ingredients. Thermophilic compost that contains any or all of these things need only be held for a year . Compost made from solely non-disease-infected vegetation can be used after six months, no matter the temperature of the pile.

Many books and articles on home composting contain long lists of things not to compost, and that list contains diseased crops, meat scraps, peanut butter , cooking oils, carnivore or omnivore feces, and so forth. Such a list of banned items makes perfect sense when dealing with mesophilic compost (or meeting organic certification standards), especially if it won't be held for a couple of years to ensure pathogen death-and most home composting is mesophilic.

But by using thermophilic composting, the list of banned items can go into the compost pile, and you can recycle all of your uneaten leftovers.

It is possible to compost human manure safely; however , the procedure isn't covered in this guide. The proper procedures for recycling human manure are thoroughly covered with extensive documentation by Joseph Jenkins in The Humanure Handbook. (Mr. Jenkins has kindly made an electronic version of the book available on the Internet at no cost. Just look for it in a search engine.)

Thermophilic Composting

Four things are required to achieve thermophilic composting: adequate bulk, adequate aeration, adequate moisture, and a proper ratio of carbon to nitrogen, known as C/N ratio.

Composting methods are usually described as either batch methods or continuous methods. Batch methods add all of the ingredients at once, while continuous methods add to the pile progressively. Most mini-farmers and home gardeners are continuous composters by default. As a result the initial stages of a compost pile may not have enough bulk to retain the heat of thermophilic composting. This problem can be solved through timing: Start new compost piles in the spring, so that by the time cool weather arrives, the pile already has plenty of bulk to retain heat through the winter.

In the spring, you not only add the leaves that fell on the yard during the fall but also harvest green manures that were planted in the fall for a spring harvest and add those to the pile as well. You can also add livestock manure (if available) and any grass clippings or remaining crop debris. This gets the pile off to a good start with plenty of bulk. If leaves aren't available, straw or hay will work just as well. The various ingredients are added to the pile in alternating layers no more than two inches thick so that grass clippings or leaves don't get matted down to form a layer impermeable to air . If you wind up with a layer a little too thick, don't worry because the next time you turn the compost pile, the layers will all get mixed up.

Aeration is important because thermophilic composting is aerobic, requiring oxygen. There are two sorts of microorganisms involved in decomposing organic materials-aerobic microorganisms that work in the presence of oxygen, and anaerobic microorganisms that work in the absence of oxygen. Aerobic composting reduces or eliminates odors and allows for thermophilic microbes, whereas anaerobic composting smells like a septic tank and seldom develops much heat. Therefore, aeration is important to make good compost and maintain peace in the neighborhood. Aeration is achieved by regularly turning over and mixing compost piles. Practically every book or article written about composting advocates frequent turning of the pile to ensure adequate aeration. The idea of turning compost is so entrenched that a number of companies even make fairly expensive gadgets for helping people turn and tumble their compost.

-------------- Drilled PVC pipe used for compost aeration.

Too much turning of compost is unnecessary and can actually be counterproductive by causing a loss of both valuable nitrogen and organic matter.

Turning a compost pile will also serve to dissipate any heat. The solution to the problem is to build the compost pile in such a way that it is self-aerating.

This is accomplished by layering in straw as you go along-just keep a couple of bales handy next to the compost pile. By adding a layer of straw and making sure that no layer in the pile of any given ingredient is more than a couple of inches thick without being broken up by either straw or another ingredient, a self-aerating pile is ensured. Or , you can try my method, in which large-diameter PVC pipes with holes drilled in them are buried vertically in the pile.

Not all piles can be constructed in a fashion that guarantees self-aeration, of course; in such cases turning the pile up to five times per year is absolutely necessary. In fact, if a pile is not self-aerating, it should be turned regularly. After prolonged heavy rains that can soak into the pile and force out the oxygen, turning is a good idea.

In addition, the composting process uses a great deal of water , so when compost is turned, water should be added as needed.

------------- Watering the pile as it is turned is important.

Adequate moisture is another important factor in composting.

Too much moisture in compost forces out the air , leading to anaerobic decomposition, which is not thermophilic and almost always smells bad. Too little moisture in compost causes the microorganisms to go dormant or work less effectively. Thankfully, the ideal range for compost is actually pretty tolerant and can be anywhere in the range of 40% to 60%, 21 and all that is required is for any dry layers added to the pile (such as leaves or sawdust) be dampened with a hose if rain isn't in the forecast. Any additional moisture needed will be supplied by rain in most of North America.

Extremely rainy climates might require that the pile be covered with a tarp on occasion, and drought conditions will require that the pile be checked and water added if its moisture content isn't about that of a wrung-out sponge. Remember , again, that when turning compost, check to see if water is needed, and add it if necessary.

Just like humans require nutrients in given amounts to be most productive, microorganisms responsible for making compost have dietary needs. The most relevant dietary requirement of microbes in the manufacture of thermophilic compost is the ratio of carbon to nitrogen in the pile. Microbes need nitrogen to build proteins, and they need carbon for practically everything. A ratio of carbon to nitrogen of 30:1 will result in thermophilic compost.

This ratio need not be followed slavishly. Microbes are picky but not that picky. Anywhere from 35:1 to 25:1 will work fine.

The proper carbon/nitrogen ratio can be achieved by mixing ingredients with higher and lower C/N ratios in approximate proportions. For example, cow manure with a C/N ratio of 20:1 can be mixed with oak leaves with a C/N ratio of 50:1 to get the desired ratio of 30:1. Even more easily, green vegetable wastes mixed half and half with dry vegetable wastes will achieve the same result. A table listing the C/N ratios of common materials is below to use as a guide.

Table 6 : Carbon to Nitrogen Ratios of Commonly Composted Materials

Material Ratio Vegetable wastes 12-20:1

Alfalfa hay 13:1 Cow manure 20:1 Leaves 40-80:1 Corn stalks 60:1 Oat straw 74:1 Wheat straw 80:1 Sawdust 100-500:1 Grass clippings 12-25:1 Coffee grounds 20:1 Poultry manure 10:1 Horse manure 25:1

If a compost pile is constructed, and it just won't seem to heat up, check the moisture and add water or drain as needed, then poke holes deep in it with a pole for aeration. If neither of these works, nitrogen needs to be added. Ideally, this would be done by mixing in green vegetation, but blood meal mixed with water and dumped into the aeration holes will work too. Blood meal is common and can be bought at garden stores and possibly the local Walmart. If my piles aren't heating up the way they should because of inadequate nitrogen, what I do is add a standard organic fertilizer containing nitrogen and a bit of compost activator every so often as I turn them.

A soil and/or compost thermometer can be purchased inexpensively so you can judge the performance of your pile. (We use a long laboratory thermometer because I have several already.) You want the pile to reach from 130 to 160 degrees for no less than 15 days total. In practice, your compost is unlikely to stay at such a temperature for 15 days in a row. By using a thermometer , you can see when the temperature is starting to drop. Mix the pile thoroughly every time you see the temperature drop, and within a couple of days, the pile will heat back up again if the moisture level is right. This way, you can be pretty certain of at least 15 days of thermophilic temperatures in your compost.

At thermophilic compost temperatures of 140 degrees, roundworm and other eggs are killed in two hours or less, and most other protozoans, bacteria, and viruses are killed within minutes.

The most tenacious dangerous germ is salmonella, and it is killed in about 20 hours.

By providing 15 days at temperatures exceeding 130 degrees, you are creating compost that is absolutely safe to apply to crops that touch the soil, practically without regard to its ingredients.

Compost Aging

As noted earlier, both temperatures and retention time have an impact on pathogen destruction, along with the biochemistry of the compost pile. For a pile made from non-diseased plants and manures, an extensive retention time is not required to ensure that the compost is hygienic, but a minimum retention time is definitely required to make sure that the compost is mature. Immature compost can contain phytotoxins that retard germination and can use up the nutrients from any beds it is added to. The standards of the Canadian Council of Ministers of the Environment specify that six months is adequate retention time for compost, and that works whether the composting has been mesophilic or thermophilic as long as diseased materials weren't used. If disease organisms were likely present (because debris from infected crops or meat products were added), then compost should be retained a year if thermophilically composted, and two years otherwise.

Proper aging of compost can be tested without a fancy laboratory using radish seeds, because radishes are extremely sensitive to the phytotoxins in immature compost.

Purchase some commercial seed-starter mix, dampen it, and put it in a seed-starting container. Put the compost to be tested in another container in the same environment as the first, then plant 20 radish seeds in each flat. Water both regularly, and keep at 70 degrees F.

Observe the germination. If the germination rate of the seeds in the compost is less than 80% of that in the commercial seed-starter mix, the compost needs to age some more.

Compost Activators

Almost every gardening magazine carries advertisements in the back for so-called compost activators. These products typically contain a mix of bacteria and fungi that help the composting process. While these products certainly won't hurt your compost, they aren't usually necessary either , because compost activators are all around you and free.

The two most useful compost activators are the prior year's compost and good garden soil. These contain a wealth of suitable bacterial and fungal spores that will seed your pile. Only a shovel or two of these mixed into the pile periodically is sufficient.

I have tried a couple of commercial compost activator products and found no difference between piles in which they had been used and piles in which they had not--except for cases where a pile has refused to heat up adequately because of lack of moisture. In these cases, adding the activator layered in with the additional water increases the rate at which the pile heats up.

The Grow Biointensive method of making compost-a mesophilic method-specifies that fully 1/3 of the final weight of your compost should be from garden soil. The reasoning for this is that it keeps the compost pile "cool" so that it will compost slowly. This has the benefit of preserving more organic matter and more nitrogen because a thermophilic phase is never reached.

We cannot deny this benefit, but I don't advocate this technique because the benefits of thermophilic composting-removing disease organisms and allowing a wider range of compost ingredients--outweigh the slightly greater loss of organic matter . So use a shovelful of garden soil or last year's compost as an activator , but don't get carried away or you'll end up with compost that won't reach high enough temperatures to kill disease organisms.

The Big Picture

Plant cover crops in the fall that are harvested in the spring and used to start a thermophilic compost pile when combined with leaves, straw, and other high-carbon materials. Add household organic wastes like food leftovers liberally to the pile, along with any animal manures available. Use straw or sawdust as a cover material when adding anything that would attract dogs or rodents or just bury it deeply in the pile. Add crop debris in the fall and then a good cover of hay or straw on top for the winter. In the spring, start a second pile, and let the first one sit for a year to cure, since uncured compost can hurt the soil's fertility; allowing a year to cure also ensures hygienic compost. The following spring, the first pile is available for use.

----------- The author's three-bin composting system.

If potentially pathogenic material has been composted or the compost never reached a thermophilic phase, it is best to hold the compost for a couple of years to be absolutely sure it is safe.

We have a three-bin system made out of chicken wire with a large bin in the center and bins half the size of the center one on either side. The larger center bin is used for current compost. By midsummer , the center pile has shrunk, and I shovel it into one of the two side bins. The next batch of compost from the center bin goes into the other side. By then, the compost in the first side is fully cured.


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Updated: Monday, February 15, 2021 8:11