MATERIALS FOR COMPOSTING

Materials for composting are all around you. Many gardeners need look no further than the home grounds for a sufficient supply. Kitchen wastes, lawn clippings, weeds and plant debris, dog and cat hair—nearly anything that once lived (and is thus organic) is a candidate for the compost heap.

After you have exhausted the home supply and still don’t have all the materials you would like, you can plan a series of foraging expeditions, beginning as close to home as possible and ranging out as far as you must in order to fulfill your requirements.

Manure should be the first item on your list, since it is by far the most important ingredient in any heap. If you try, you can get it free for the hauling or at a token fee at poultry farms, riding stables, feedlots, even zoos and wild game farms—any place that holds large numbers of animals in concentration. Even a friend with one horse and no garden can supply all the manure you’ll need for a backyard pile.

Your chances of getting manure at a family farm are not as good, since farmers will probably want their manure for their own fields. Even if you seem to have all the home materials your compost heap can use, try to find a source of manure. Its tremendous bacteria content will bring your heap into biological and chemical balance and aid the rapid reduction of all the other materials.

But you don’t have to stop with manure expeditions. In town, you can scavenge at grocery stores, city agencies, factories and mills, restaurants, and many retail operations. Ranging farther into the country, you can find materials in fields and along roadsides, streams, and ponds; at farms and orchards; at sawmills and canneries. Nearly any organic gardener can locate ample composting materials by going no farther than 5 miles from home. The farmer, of course, must make composting an integral part of his or her soil management plan, utilizing every scrap of home material and adding green manure crops as necessary. Even the organic farmer—especially one who has few animals or cultivates a small but intensive area—might need to look for supplementary materials. The materials listed in this chapter can be of use to both gardeners and organic farmers seeking to enhance their composting operations.

WHERE TO BEGIN

Begin, of course, at home. Are you discarding any organic matter at all? Newspapers? Tea bags? Clippings from the children’s haircuts? Dishwater? With the exception of human and pet excreta (addressed later in this chapter), you can use everything. Before foraging, be sure that your home recovery program is 100 percent effective.

Once you venture outside your own yard, the best place to start is with friends, neighbors, and relatives. Some diligent composters offer to cart away kitchen scraps after every social call. This is often a valuable community service for people who would like to compost their wastes but for one reason or another are not able to do so. Recycled plastic pails with tight-fitting lids, such as those used for wallboard compound, make excellent containers for storing a week’s worth or more of goodies. A layer of peat moss or sawdust on the bottom helps absorb moisture and odors. You can offer to pick up the full pail regularly and leave a fresh, empty one in its place.

Your expeditions away from home can continue with a trip through the business directory of the phone book. Go through it slowly, listing all possible sources of materials. Your search might end when you find that you can pick up manure at the local riding stable every Saturday morning and vegetable trimmings from the neighborhood supermarket every Tuesday and Friday afternoon. After your routine is established, it usually operates like clockwork.

Here is a partial list of away-from-home materials. You will come across others in your expeditions—but do consider these for starters.

Farms and orchards. These can provide spoiled hay, corn silage, eggshells, manure of every kind, feathers, barnyard litter, spoiled fruit, spent mushroom soil, whey from dairy operations, and orchard litter.

Factories and mills. Apple pomace is available from cider mills. Other possible compostables include cannery wastes of all kinds; shredded bark, sawdust, and wood shavings from lumber mills and carpentry shops; botanical drug wastes from pharmaceutical firms; cement dust; cocoa bean hulls (good mulch); coffee chaff from coffee wholesalers; cottonseed meal; felt wastes; agricultural frit from glass factories; grape pomace from wineries and spent hops from breweries; granite dust from cutting operations; leather dust; lignin from paper mills; spoiled meal from flour mills; peanut shells; slag from steel plants; spice marc (spent) from spice packers; tanbark from tanneries; tankage from meat-processing plants and slaughterhouses.

The search for a variety of composting materials should begin at home.

Stables and feedlots. Manure and stable litter of all kinds are valuable compostables.

Retail stores. You can get vegetable trimmings from supermarkets and shops, hair from barbers and salons, pet hair from grooming parlors, food wastes from restaurants, coffee grounds from cafés, shredded paper store offices, plant wastes from florists, and sawdust from carpentry shops and lumber supply houses.

Roadsides, fields, and waterways. Rural road and power line maintenance crews who cut brush and trees will often deliver loads of wood chips to your site. Old leaves, weeds, and water plants from streams, lakes, and ponds may be plentiful. A note of caution: Many native plants, even those viewed as weeds, are endangered species that are protected by law. This is especially true of plants growing near oceans or in wetlands; such areas often contain fragile ecosystems that should not be disturbed. In gathering materials in fields and wild areas, be aware of your ecological responsibility to avoid robbing natural areas of their native plants.

REGIONAL MATERIALS

Gardeners in certain parts of the country can avail themselves of materials abundant in their regions. New Englanders can look for sawdust, dairy manure, and maple syrup wastes. Those along seacoasts can find greensand, fish scraps, and seaweed. Southwestern gardeners should look for cannery wastes, mesquite, olive residues, grape pomace from wineries, and citrus wastes. Southerners may have access to cotton gin trash, Spanish moss, peanut shell ashes, tung oil pomace, sugarcane trash, molasses residue, castor pomace, tobacco stems, rice hulls, and water hyacinth plants.

In collecting materials for your heap, not only will you be adding to your own soil’s fertility and structure but you will also be contributing to the recycling of wastes that might otherwise become pollutants in the environment. Many communities now have or are planning composting facilities for at least part of their trash. If yours is one of them, they probably make finished compost available free or at low cost to gardeners. Chapter 13 has more information about using municipal compost. If your town has not yet pursued this option, it may offer free delivery of leaves, shredded tree trimmings, and other compostable municipal wastes.

Supermarkets and restaurants may be happy to contribute their organic wastes to you, since it lowers their disposal costs. Increasingly, such large organic waste generators are required to separate out compostable material to keep it out of landfills. Most important, however, these materials, instead of being dumped, buried, or burned, will find their way back to the soil.

MATERIALS TO AVOID

Although nearly any organic material can contribute to good compost, there are some that should be avoided, and others should be used only in limited amounts. First, you want your heap to be balanced among green matter, animal wastes, manure, and soil. If you build your heap of 80 percent tankage from the local meat-packing plant, not only will you have a putrid mess, but you will attract every stray dog, cat, and raccoon within a 5-mile radius. A truckload of grape pomace or a ton of wet hops from the brewery will be equally hard to handle, as will be the neighbors if your heap’s odor wafts their way. Strive, then, for a commonsense balance in the materials you select, and be sure to add a layer of soil over the heap every time you add materials that might cause odor or attract vermin.

Human feces should not be used unless they have been properly treated and permitted to age sufficiently. Even then, concerns about disease pathogens make it best to avoid such material or to use it strictly for ornamentals. Urine alone can be used quite safely, however. See Chapter 5 for a discussion of humanure use.

Wastes from pet dogs, cats, and birds should not be used on the compost pile. Although dog manure is as rich in nutrients as other manures, it is more difficult and less pleasant to handle than the mixed bedding and manure of cattle and horses. In addition, it may carry organisms parasitic to humans. Special composters designed exclusively for dog droppings offer pet owners a safe alternative.

Cat manure is even more hazardous, especially to pregnant women and small children. Cat droppings may contain Toxoplasma gondii, a one-celled organism that, when transmitted to a pregnant woman, may infect her unborn child, causing brain and eye disease. Toxocara cati is a roundworm, also common in cat feces, that causes similar problems in children. Keep the contents of the litter box away from children and the compost pile.

Bird droppings have been similarly indicated as potential disease sources. Since they are most often mixed with bedding and dropped birdseed from the bottom of the cage, bird droppings will also tend to introduce unwanted weeds into your compost.

Materials that will not decompose readily—large pieces of wood, oyster and clam shells, large quantities of pine needles, rags, brush, cornstalks, heavy cardboard—should not be used in large amounts unless they are shredded first.

Large amounts of highly acidic materials such as pine needles and oak leaves should not be used without the addition of enough limestone to neutralize the acid. For acid-loving crops, however, you might wish to build acidic compost by the deliberate use of these materials.

Be very careful about diseased plants—you may be better off burning them and adding the ashes to your compost than risking inoculating your whole garden with them. Weeds can generally be composted, but be careful to ensure hot composting temperatures if they have produced seed. A few species, such as quack grass and Canada thistle, reproduce readily from the tiniest bit of surviving rhizome and should be avoided entirely.

Don’t use large amounts of grease and oil, since they not only attract animal pests but also inhibit the biochemical processes necessary to successful composting. The amount of grease and oil from a normal household will cause no problem. However, carting home tubs of spent grease from the local potato chip factory is unwise.

Do not use toxic materials. There is little sense in trying to build an organic soil by including pesticide-treated wastes in the compost heap. Plant debris from roadsides might have been subject to a broad, potent, and persistent herbicide applied by the highway department. Similarly, green waste from municipal parks may have been treated with pesticides and herbicides used in grounds maintenance. Be careful in choosing materials.

MATERIALS FOR ENRICHMENT

There are many substances you can buy to increase your compost’s N-P-K content or control its pH. Although it is not necessary to add these materials to the heap, many gardeners find it worth the expense to ensure a high nutrient level in their compost.

Among the materials and products available at garden centers and through mail-order outlets are bagged manure, vermicompost, dried blood, bonemeal, limestone, cottonseed meal, greensand, hoof and horn meal, tobacco wastes, seaweed, peat moss, and other natural products that are valuable to the heap because of their nutrient levels or ability to correct pH. All will be considered later in this book.

Many people add lime to their compost to increase its pH. This is not often necessary or beneficial, and it is not a good idea if you are composting manure, since the lime reacts with the nitrates in the manure to drive off ammonia. If lime is needed, apply it directly to the soil or mix it with the finished compost for potting mixes. The microbes inhabiting your compost heap can often benefit from the calcium in lime, but other forms of calcium, such as eggshells or any marine animal (oyster, crab, clam) shells, pulverized as finely as possible, will serve just as well. Bonemeal and wood ashes are also rich in calcium. Avoid all of these materials if you want compost for acid-loving plants such as rhododendrons, camellias, and blueberries, in which case you may want to use acidic peat instead of soil in your heap.

Rock or colloidal phosphates are excellent materials for enriching the mineral content of your compost. Microbial action makes their nutrients more readily available than they would be if they were added directly to the soil. They also contain significant amounts of calcium and micronutrients. Other rock powders such as granite dust and greensand, both sources of potassium and micronutrients, are similarly made more available to plants when first consumed by compost organisms.

Specific nutrients can be added by using plants that are especially rich in those elements in your compost. Seaweeds, such as the kelps, are rich in potassium and are good sources of such elements as iodine, boron, copper, magnesium, calcium, and phosphorus. If available locally, seaweed should certainly be added to the compost heap. The water hyacinths that grow so abundantly in the rivers of the South are rich in many of the elements that are more apt to be deficient in the soil. Leaves, discussed more thoroughly later in this chapter, are a teeming source of micronutrients that are not found in upper layers of soil; use them in compost whenever possible.

Refer to the lists beginning on this page for other materials that are particularly high in nitrogen, phosphorus, and potassium.

ACTIVATORS

A compost activator is any substance that stimulates biological decomposition in a compost pile. There are organic activators and artificial activators. Organic activators are materials containing a high amount of nitrogen in various forms, such as proteins, amino acids, and urea, among others. Some examples of natural activators are manure, garbage, dried blood, compost, humus-rich soil, and urine.

Artificial activators are generally chemically synthesized compounds such as ammonium sulfate or phosphate, urea, ammonia, or any of the common commercial nitrogen fertilizers. These materials are not recommended.

There are two ways in which an activator may influence a compost heap: (1) by introducing strains of microorganisms that are effective in breaking down organic matter and (2) by increasing the nitrogen and micronutrient content of the heap, thereby providing extra food for microorganisms.

Those who follow the practices of biodynamic agriculture consider certain activators, made according to precise instructions, to be essential for producing the highest-quality compost. These preparations are used in minute quantities as part of a holistic approach to working with soil, plants, and the energies of nature. The biodynamic method is explained more fully in Chapter 8.

Claims have sometimes been made that special cultures of bacteria will hasten the breakdown of material in a compost heap and also produce a better quality of finished compost. Products are manufactured that are reported to be effective in improving the action of a compost heap.

Most independent tests, however—including those conducted at the Rodale Institute—indicate that there is no benefit to be gained from the use of an activator that relies solely on the introduction of microorganisms. It seems that microorganisms will quickly multiply to the limit that their environment will permit. Since all the necessary microorganisms are already present in manure, soil, and other composting materials, there is no benefit to be gained from introducing strains in the form of an activator product. The best activator is a layer of finished compost from the previous heap or a generous amount of healthy topsoil.

Biochar, a form of charcoal created by heating carbonaceous material under conditions of low oxygen, is often touted as an all-around elixir for stimulating soil biology. There is increasing evidence that mycorrhizal fungi in particular are more abundant in biochar-amended soils, where their mycelia find hospitable conditions of moisture and aeration. The large amount of surface area offered by biochar particles provides an ideal environment for microbial colonization.

Commercial biochar-based products have proliferated in recent years. Quality of the raw input, particle size, and process controls are all variables that determine the effectiveness of the product. According to David Yarrow, a midwestern “carbon-smart” farm consultant, a potent inoculant can be obtained by mixing some good-quality compost with biochar consisting of different-size particles, a full complement of micronutrients, and enough water to keep it moist but not soggy. A sugar source such as molasses is sometimes added as a way to jump-start bacterial growth. This well-blended mixture should sit undisturbed as long as possible to allow a full diversity of microbes to colonize the material. Most often used to restore depleted soils, such concoctions can also be of value in boosting microbial populations in compost that may be lacking in manure or other highly biologically active ingredients.

Nitrogen Activators

The cause of most compost heap “failures” is a lack of nitrogen. Almost invariably, a heap that doesn’t heat up or decay quickly enough is made from material that is low in nitrogen. Nitrogen is needed by the bacteria and fungi that do the work of composting, to build protoplasm and carry on their life processes.

In experiments conducted at the Rodale Institute, it was shown that increasing additions of bloodmeal (a high-nitrogen activator) produced associated increases in the temperature of the pile, indicating increasing bacterial activity. In the tests, 3 pounds of bloodmeal in a 31-pound pile produced the best results.

Good nitrogen activators besides bloodmeal (which is expensive when purchased commercially at garden centers) include tankage, manure, bonemeal, and alfalfa meal. Human urine, which contains about 1 percent nitrogen, also makes an excellent compost activator. Just how much you should add to the heap depends on the nature of the material you are composting. Low-nitrogen materials such as straw, sawdust, corncobs, and old weeds should have at least 2 or 3 pounds of nitrogen supplement added per 100 pounds of raw material. If plenty of manure, grass clippings, fresh weeds, and other high-nitrogen materials are available to be mixed in with the compost, no nitrogen supplement will be necessary.

COMMON MATERIALS

Here is a list of the more common—and some not-so-common—materials that can be used in composting.

Alfalfa

Alfalfa is a perennial herbaceous legume grown as livestock feed and as a green manure or cover crop. Alfalfa grows almost everywhere in the United States and is widely available as hay, meal, or dehydrated feed pellets. Its nitrogen content and absorbency make it an excellent addition to the compost pile.

In combination with leaves and/or household garbage, alfalfa serves as a good compost stimulant and activator; its 12:1 carbon/nitrogen (C/N) ratio helps bring the pile’s overall C/N ratio into the desired 25:1 to 30:1 range. While expensive when sold as hay, alfalfa is moderately priced in the form of dehydrated pellets or meal, and these products can be purchased at most feedstores. Farmers and feedstores may also have rotted or spoiled bales, unsuitable as animal feed, that they will gladly give you.

Apple Pomace

Anyone who presses his or her own cider produces heaps of this sweet pulp. Yellow jackets, hornets, and bees love to zero in on the residues, so it’s best to get the pomace into a working compost heap as soon as possible. Fresh pomace is wet and heavy and should be mixed well with dry leaves, hay, or other absorbent matter.

While low in nitrogen, pomace does contain valuable amounts of phosphoric acid and potash. Large numbers of seeds are also present in pomace; these storage organs contain reserves of phosphorus and nitrogen, adding to the nutrient value of the pomace.

If you collect pomace from commercial presses, look into the source of their apples and the pesticides applied to the fruit. Apple skins may contain residues of metallic sprays, especially if such sprays are used heavily. Spray residues can build up to toxic levels when large amounts of pomace are used.

Bagasse

Bagasse is the waste plant residue left from the milling of sugarcane. Gardeners in the Deep South may have access to quantities of this valuable addition to the compost heap. (See also “Sugar Wastes” on this page.)

Banana Residue

The skins and stalks of this tropical fruit contain abundant amounts of phosphoric acid and potash. Banana skins decompose rapidly, a sign that the microbes of decay are well supplied with nitrogen. Banana skins are usually a staple in kitchen scraps, and their use in a compost heap will guarantee lots of bacterial activity. Incorporate banana skins into the core of your compost pile, or cover them quickly with organic matter to avoid attracting flies.

Basic Slag

This industrial by-product, formed when iron ore is smelted to make pig iron, is most commonly found in steelmaking areas. The smelting process uses large amounts of limestone and dolomite that combine with impurities in the ore, rising as a sludge that coats the surface of the molten metal. Skimmed off, cooled, and hardened, the resultant slag contains numerous minerals also found in the soil—calcium, magnesium, silicon, aluminum, manganese, sulfur, and iron—plus trace amounts of boron, chromium, copper, molybdenum, potassium, sodium, strontium, tin, vanadium, zinc, and zirconium. The exact percentage of these minerals depends on variations in the smelting process. Basic slag provides calcium (in the form of calcium silicate), magnesium, and slow-release phosphate. Often used as a liming agent, it makes other essential nutrients more accessible and protects plants from potentially toxic elements such as manganese and aluminum.

The “Composition of Slag” table on this page shows the main elements found in slag, the compounds in which they most often occur, and the average range of each mineral.

Packaged slag has been pulverized into a fine black powder so it can be used as a soil builder in gardening and farming. The material is alkaline and is popular as a liming agent. Tests show that slag is better for this purpose than lime because of its greater store of minerals.

Since slag is made up of finely pulverized but insoluble particles, it can be applied liberally to soil or a compost heap with no fear of overuse. It won’t burn plants or roots. Beans, peas, clover, vetches, alfalfa, and other leguminous crops will benefit from its application. Slags vary in content, so check the analysis before using them. Avoid slags with low or nonexistent amounts of nutrients and minor elements. Don’t use slags containing excessive amounts of sulfur.

Beet Wastes

Residues from sugar beet processing are commonly used for livestock feed, though they will compost readily. The nitrogen content averages 0.4 percent, potassium content varies from 0.7 to 4.1 percent, and phosphoric acid content ranges from 0.1 to 0.6 percent. Dried beet pulp is also available at many feedstores. Organic farmers cannot use sugar beets as livestock feed, since virtually all of the sugar beets produced in North America are genetically modified varieties. However, genetically modified plant materials can be used as compost feedstock. (See “GMO Wastes,” this page.)

Bonemeal

A slaughterhouse by-product, the pulverized residue of bones is, along with rock phosphate, a major source of phosphorus for the farm and garden. Bonemeal also contains a large percentage of nitrogen, though the content of both minerals depends on the age and type of bones processed. Raw bonemeal usually contains 20 to 25 percent phosphoric acid and 2 to 4 percent nitrogen. Steamed bonemeal, the more commonly available variety, has up to 30 percent phosphorus and 1 to 2 percent nitrogen. Steamed bonemeal is finer than raw bonemeal, so it breaks down more rapidly in the soil or compost heap.

Bone black is charred bone that has been used as a filter for sugar refining. Bone black contains about 1.5 percent nitrogen, 30 percent phosphoric acid, and many micronutrients.

Bonemeals are most effective when mixed with other organic matter and added to well-aerated soils. They will exert an alkalizing effect because of their lime content, so match their use to your soil’s pH characteristics. Use them moderately in composting to avoid the volatilization of nitrogen to ammonia.

Buckwheat Hulls

Buckwheat is a cereal crop grown mainly in the northeastern United States and in Canada. Popular among organic farmers and gardeners as a green manure and bee forage crop, it grows well in even marginal soils. Buckwheat hulls, left after processing of the grain, are lightweight and disk shaped. They make good additions to the compost heap, though many gardeners prefer to use them as mulch. The hulls absorb water easily, stay in place once applied (a layer 1½ inches thick will suffice), and look like a crumbly loam.

Castor Pomace

Castor pomace is the residue left after the oil has been extracted from the castor bean. It is widely used as an organic fertilizer in place of cottonseed meal, because the latter is a valuable feed. The nitrogen analysis of castor bean varies from 4 to 6.6 percent, while phosphoric acid and potash have been found to be 1 to 2 percent, with greater variation occurring in the phosphorus content.

Where animal matter is unavailable, compost can easily be made with castor pomace and other plant matter. Moisten the pomace and spread it over the green matter in semiliquid form. The finer the plant matter, the quicker the bacterial action.

Citrus Wastes

Gardeners living near factories producing orange and grapefruit products should make use of this easily composted residue, though dried citrus pulp is also available in bulk from some feedstores. The nitrogen content of these materials varies according to the type of fruit and the density of the skin. The thicker the peel, the more nitrogen it contains.

Orange skins contain about 3 percent phosphoric acid and 27 percent potash (surpassed only by banana skins, with 50 percent potash). Lemons are higher in phosphorus but lower in potash than oranges. Grapefruits average 3.6 percent phosphoric acid, and their potassium content is near that of oranges.

You may use whole waste fruits (culls) in the compost pile, although their nutrient content will be lower due to the high water content. Citrus wastes will break down faster if shredded (the bagged, dried pulp sold as animal feed comes in dime-size chips) and mixed with green matter and a source of nitrogen and bacteria like manure, lawn clippings, or garden soil.

Unfortunately, citrus crops are routinely sprayed by commercial growers. If the spray program is moderate, the chemicals should break down during the composting process without causing harm. To be absolutely sure of what you’re adding to your compost, use only fruits and fruit wastes from organic growers.

Cocoa Bean Shells

These residues from chocolate factories are available in bulk from garden supply houses, but because they make such an attractive mulch, cocoa bean shells rarely find their way into the compost heap. They are rich in nutrients, though, and benefit the soil however they’re used. Cocoa shell dust has 1.5 percent phosphorus, about 1.7 percent potassium, and 1 percent nitrogen—a high analysis of the latter, considering the woody nature of cocoa.

If the shells themselves have been treated to extract caffeine and theobromine, the residues will have about 2.7 percent nitrogen, 0.7 percent phosphoric acid, and 2.6 percent potassium. Untreated raw shells show a higher nutrient content. Pressed cocoa cake has also been offered as fertilizer. It’s higher in nitrogen, has less potassium than shells, and has a phosphorus content of nearly 0.9 percent. The nitrogen content of cake will vary according to its processing.

If you can locate a source of oil-free and theobromine-free cocoa wastes, you’ll have a useful product for mulching acidic soils. The extraction process uses lime, so the shells will help raise the pH while adding moisture-retentive organic matter. Cocoa shells are also weed-free and odorless.

To use them as mulch, spread the shells in a layer 1 inch deep. They are light brown, look nice around shrubs, evergreens, and flowerbeds, and offer excellent drought-proofing and insulative properties. Shells used in compost piles should be shredded or pulverized.

Coffee Wastes

Earthworms seem to have a particular affinity for coffee grounds, so be sure to use these leftovers on the compost pile, in your worm box, or as a mulch. The grounds are acidic and can be used by themselves around blueberries, evergreens, and other acid-loving plants. Mix the grounds with a little ground limestone for plants needing alkaline or neutral soil.

The nutrient content of coffee residues varies according to the type of residue. Grounds have up to 2 percent nitrogen, 0.33 percent phosphoric acid, and varying amounts of potassium. Drip coffee grounds contain more nutrients than boiled grounds, though the potassium content is still below 1 percent. Other substances found include sugars, carbohydrates, some vitamins, trace elements, and caffeine.

Coffee processing plants sell coffee chaff, a dark material containing over 2 percent nitrogen and potassium. Chaff is useful either as a mulch or in compost.

Apply your coffee grounds immediately, or mix them with other organic matter. They hold moisture extremely well. Left standing, they will quickly sour, inviting acetobacters (vinegar-producing microbes) and fruit flies.

Corncobs

These residues used to be available in large amounts from mills, but modern combines now shred the stalks and expel the cobs right back into the field. Cobs contain two-thirds of the nutrients found in the corn kernel, but they must be shredded before composting or their decay will take years. Let the cobs age in open piles for several months, then grind them with a shredder or lawn mower.

Cobs have superior moisture retention and make effective mulches when spread 3 to 4 inches deep. Shredded cobs may also be used as a seed-starting medium. In long-standing, no-turn piles, unshredded cobs mixed with leaves and other dense materials will provide aeration and discourage caking and matting.

Cottonseed Meal

Cottonseed meal is made from cottonseed that has been freed from lints and hulls and deprived of its oil. Since cottonseed cake is one of the richest protein foods for animal feeding, relatively little is available for use as fertilizer. Although it is a rich source of nitrogen, it may also contain high levels of pesticide residues. This is because cotton, as a nonfood crop, receives heavy applications of pesticides, some of which may accumulate in the seeds. Unless you have access to meal from organically grown cotton, you may choose to avoid cottonseed meal in favor of another nitrogen source for your compost pile. Organic farmers may use conventional cottonseed meal as a fertilizer if it has been tested for pesticide residues and determined to be free of such prohibited substances. (See “GMO Wastes,” this page.)

Cottonseed meal is commonly used to increase soil acidity for acid-loving specialty crops, but other materials, such as pine needles and peat moss, will serve the same purpose. Cottonseed meal has a nitrogen content of around 7 percent. Its phosphoric acid content is between 2 and 3 percent, while potash is usually 1.5 percent.

Dried Blood

Dried blood is a slaughterhouse by-product. It is high in nitrogen, about 12 percent, but its phosphorus content varies from 1 to 5 percent. Dried blood is used mainly as an animal feed, though most garden shops carry it for use as a fertilizer. The cost per pound can be quite high because it is tied to the price of meat. Dried blood can be applied directly to the soil around plants, but it should be kept several inches away from the stems to avoid burning. Dried blood may be used in compost heaps. Sprinkled over layers of moist organic matter, its high nitrogen content stimulates decay organisms, especially when added to carbon-rich materials.

Felt Wastes

Check hat factories for discarded hair, wool, and felt. These materials may contain up to 14 percent nitrogen and will aid in making rapid, high-heat compost. Such wastes are quite dry, however, and will decompose slowly or pack down unless they are thoroughly moistened and mixed with bacteria-rich ingredients like manure or green matter.

Fish Scraps

Gardeners near oceans or fish-processing plants can usually truck home loads of this smelly stuff. It is well supplied with nitrogen and phosphorus (7 percent or above for each nutrient) and also contains valuable micronutrients like iodine. But, like all fresh residues, fish scraps easily turn anaerobic and are highly attractive to rodents, flies, and other scavengers.

Fish scraps must be handled carefully in the garden, either buried (covered with at least 4 inches of soil) or composted in properly built heaps enclosed by sturdy bins or pens. The trick is to use generous amounts of bulky, high-carbon materials such as shredded brush, straw, or sawdust to balance the high nitrogen and moisture of the fish, to increase aeration, and to discourage packing down.

Composting fish scraps in a pit is somewhat easier (once you’ve dug the pit, of course). Mix them with organic matter or soil and cover them with enough dirt to discourage flies. The pit must also be enclosed by a sturdy fence or wall and topped with a scavenger-proof frame or lid.

Fish scraps present difficult challenges to the composter on any scale, but offer ample benefits when used with reasonable care and attention to providing adequate carbon and air. Dr. William F. Brinton, of Woods End Research Laboratories in Maine, has successfully demonstrated fish waste composting, with minimal odor problems, using a farm- or industrial-scale windrow method.

Crab meal is becoming a popular organic-approved fertilizer readily obtained through garden supply stores. Besides serving as a good source of nitrogen, phosphorus, calcium, and essential micronutrients, crab shells are high in chitin, which suppresses some plant pathogens and parasitic nematodes as it decomposes under bacterial action.

Garbage

Americans routinely throw away mountains of valuable food scraps, setting them out on the curb or grinding them up in disposals and flushing them into overworked municipal sewage systems. Yet kitchen scraps are truly a neglected resource, containing 1 to 3 percent nitrogen along with calcium, phosphorus, potassium, and micronutrients. The material is free, available in quantity every day, and relatively easy to handle.

Kitchen scraps may be dug directly into the garden (see “Trench and Posthole Composting” on this page). Alternatively, they may be composted in heaps or pits. You can conveniently save household garbage until you are ready to layer it into a new or existing compost pile. Use a plastic bucket with a tight-fitting lid, and each time you add garbage, cover it with a layer of sawdust or peat moss to absorb moisture and odors. When adding kitchen scraps to your compost pile, mix them well with absorbent matter like dead leaves or hay to offset the wetness. Use a predator-proof enclosure, and be sure to keep all scraps well into the pile’s core, covering them thoroughly with dirt or additional materials to discourage flies.

Chop or shred all large pieces of matter (potatoes, grapefruit rinds, eggshells, and so on) to hasten decomposition. Meat scraps, fat, or bones should be used with caution in compost piles, for these materials take too long to fully break down and are most attractive to scavenging animals.

GMO Wastes

An extremely difficult issue is that of organic wastes derived from genetically modified organisms (GMOs). Corn, soybeans, canola, potatoes, rice, cotton, alfalfa, and sugar beets now could all possibly be GMOs, which are not permitted to be used to produce an organic product, according to the National Organic Program. However, waste products from crops like corn and alfalfa may be used as fertility inputs. Research is still inconclusive as to how completely the composting process breaks down the genetically altered DNA, and there are no definitive limits (at least in the United States) for GMO contamination in an organically grown product. In the case of wastes of crops that may be GMOs (e.g., spoiled corn silage), it is best to make sure that the material was not grown from genetically modified seed. There is, however, no clear evidence that GMOs in the feedstocks will remain in the finished compost.

Gin Trash

Gin trash is another by-product of the cotton industry. Once burned and discarded, these leaf and stem wastes are now being composted and returned to the soil. While cotton wastes contain many valuable nutrients and fibrous organic matter, their effect on soil health may not always be beneficial, depending on the type of cotton and the state in which it was produced. In some states, including Texas and Oklahoma, arsenic compounds may be applied as a defoliant and desiccant. Significant residues of this carcinogen are left in the gin trash, making it an undesirable addition to the compost pile. Normal arsenic levels in the soil run about 5 parts per million, but gin wastes may contain 40 times that amount.

Although arsenic acid may no longer be used in cotton production, organic forms of arsenic are still legal for use as a defoliant. Home composters who have access to gin trash should consider its source and the production methods used in their state before making gin trash a part of their composting program. Because of the timing of arsenic applications, contamination of the seeds does not occur; arsenic residue is not a concern with cottonseed meal. (See “Cottonseed Meal” on this page.) In some parts of Texas and California, gin trash from organically produced or “eco-grown” cotton may be available. If you have cotton gins in your area, check with their operators to find out about the types of cotton crops they handle.

Granite Dust

Granite dust is a natural source of potash that is superior to the chemically treated potash sold as commercial fertilizer. Granite dust or granite meal has a potassium content of between 3 and 5 percent, contains micronutrients, is inexpensive, and will leave no harmful chemical residues. Unlike chemically treated sources of potash, granite dust is slow acting, releasing its nutrients over a period of years. It may be used in the compost pile or added to soil or sheet compost. Use it liberally directly on the soil, applying 10 pounds to 100 square feet when spreading. Choose a windless day for application, and wear a dust mask.

Grape Wastes

Wineries produce these residues of skins, seeds, and stalks by the ton during the pressing season. Vineyards also accumulate large amounts of grapevine pieces after annual pruning. While the nutrient content of grape wastes isn’t that high, the sheer bulk of organic materials involved benefits the soil by promoting aeration and microbial activity.

The residues of pressing will be wet and mushy and should be mixed with absorbent plant matter. Additional nitrogen in the form of manure or high-protein green matter may be necessary if you desire rapid, hot compost. The prunings are tough and must be chopped into pieces 3 to 6 inches long, or shredded, if they are to break down in a season.

Grass Clippings

This is one compostable—a true “green manure”—that most gardeners can produce or obtain in abundance. Even if you don’t have your own lawn, your fellow citizens do; in suburban areas they’ll leave bags of clippings conveniently lined up along the curbsides for your harvesting every garbage collection day.

Freshly gathered green clippings are exceedingly rich in nitrogen and will heat up on their own if pulled into a pile, but because of their high water content, they will pack down and become slimy. This can be avoided by adding grass clippings in thin layers, alternating with leaves, garbage, manure, and other materials, thus preventing them from clumping together. If you discover a mass of matted clippings when you turn your compost, just break it up with a garden fork or spade and layer the pieces back into the pile. Grass clippings and leaves can be turned into finished compost in 2 weeks if the heap is chopped and turned every 3 days. You can profitably mix two parts grass clippings with one part manure and bedding for a relatively fast compost, even without turning.

Clippings that have been allowed to dry out will have lost much of their nitrogen content but are still valuable as an energy source and to absorb excess moisture. Clippings make an excellent mulch in the vegetable or flower garden or around shrubs and trees. As a mulch, clippings look neat and stay in place, and only a light layer (3 to 4 inches) is needed to choke out weeds and seal in moisture.

If you have extra grass clippings on hand later in the season, use them as a green manure. Simply scatter them in an area that has already been harvested and turn them in immediately, along with any previously applied mulch. The fresh clippings decompose quickly in the soil and stimulate microbial activity by providing abundant nitrogen. More mulch should be added to the surface over winter to prevent exposure of bare soil to the weather. Additionally, you can use clippings as a green manure before planting a late crop, but give the soil a week or 10 days to stabilize before planting. When used this way, grass clippings greatly improve the physical condition of heavy-textured soils.

Not all grass clippings should be removed from the lawn; when left after mowing, their nutrients enrich the lawn itself, without the application of chemical fertilizers. However, most lawns do not need as much enrichment as a full growing season’s clippings will provide. Collecting grass clippings also helps reduce weed growth by removing weed seeds from the lawn.

There is one environmental caution about grass clippings. Many homeowners use various “weed and feed” preparations or any of a half-dozen herbicides in striving for an immaculate lawn. The most troublesome of these chemicals is 2,4-D, a weed killer that has caused birth defects in lab animals and may be carcinogenic.

Although this systemic, rapid-action plant hormone attacks broad-leaved plants like dandelions, literally causing them to grow themselves to death in hours, 2,4-D doesn’t affect grasses. The narrow-bladed leaves do absorb traces of the hormone but not enough to harm them. Much more 2,4-D remains as a residue in broad-leaved plants, though even this should theoretically be broken down by soil microbes in a week. But beware of grass clippings that may have spray adhering to them from a fresh application. If used as a mulch, such clippings could cause herbicide damage to your garden plants—most of which are broad-leaved.

Ask your neighbors or whomever you gather clippings from what they used on their lawns. (If several mowings and some rains have occurred since the last application of herbicide, the clippings should be clear of 2,4-D residue.) Use your own clippings if you have them, and look around for natural lawns showing a healthy crop of dandelions—a sign that the landowner wisely avoided using herbicides.

LETTING THE CLIPPINGS FALL

Leaving grass clippings on your lawn some of the time provides the grass with natural fertilizer and saves work. It is recommended in Grasscycling, a lawn care plan designed by the Professional Lawn Care Association of America. The low-maintenance lawn care plan is based on the highly successful Don’t Bag It program originally developed in Texas. Leaving clippings does not cause thatch buildup, as was once believed. Thatch is made up of dead roots, leaf sheaths, and rhizomes, not clippings. If you mow with a regular lawn mower, don’t let the grass grow more than 1½ inches between mowings, and mow the grass only when it is dry. Even so, the clippings can be messy.

Mulching mowers eliminate the mess by chopping the clippings into fine fragments after they cut the grass. The fragments fall down into the lawn, where they decompose rapidly and release nutrients. Mulching mowers can also shred a few fallen leaves on the lawn while you are mowing and can be used to prepare piles of leaves for composting.

Mulching lawn mowers chop grass clippings into fine bits that break down quickly to return nutrients to the lawn.

Greensand

Greensand is an iron-potassium silicate that imparts a green color to the minerals in which it occurs. Being an undersea deposit, greensand contains traces of many (if not all) of the elements that occur in seawater. Greensand has been used successfully for soil building for more than 100 years. It is a fine source of potash.

Greensand contains from 6 to 7 percent of plant-available potash, but it is released very slowly when applied directly to the soil. Incorporating greensand into your compost improves the availability of its potassium and micronutrients. Good glauconite deposits also contain 50 percent silica, 18 to 23 percent iron oxides, 3 to 7.5 percent magnesia, small amounts of lime and phosphoric acid, and traces of more than 30 other elements useful to higher plant life. Unlike wood ashes, another frequently used source of potash, greensand does not have an alkalinizing effect.

Hair

Between 6 and 7 pounds of hair contain as much nitrogen as 100 to 200 pounds of manure. Like feathers, hair will decompose rapidly in a compost pile but only if well moistened and thoroughly mixed with an aerating material. Hair tends to pack down and shed water, so chopping or turning the pile regularly will hasten decay. Most barbershops or hair salons will be happy to supply you with bags of hair (though they may think your request is strange unless you explain).

Hay

Farmers often have spoiled hay available free or at low cost to gardeners. Hay is an excellent source of carbon for compost and also contains significant amounts of potassium, especially if it includes legumes such as alfalfa, clover, or vetch.

Hay is sometimes best used as mulch, especially around fruit trees. However, unless it was cut early, before seed heads began to form, it poses the hazard of introducing weed seeds into your garden. High-temperature composting will kill most weed seeds. To ensure that high enough temperatures (above 140°F/60°C) are reached, you should chop or shred the hay first, especially if it has matted in the bales. This can be done by spreading out the sections and running a lawn mower back and forth over them. You should alternate layers of nitrogenous materials such as manure with the shredded hay, to stimulate rapid heating. Make sure the materials are moist enough by giving each layer a good sprinkling. If high enough temperatures are not reached within a couple of days, the pile should be turned and re-layered with an additional nitrogen source.

Hoof and Horn Meal

There are many grades of hoof and horn meal. The granular form breaks down with some difficulty unless kept moist and well covered; it also tends to encourage the growth of maggots because it attracts flies. Finely ground horn dust, which gardeners use for potting mixtures, is quite easily dissolved. The nitrogen content is from 10 to 16 pounds per 100-pound bag, or as much as a ton or more of manure, while the phosphoric acid value is usually around 2 percent. If available, this is a very handy source of nitrogen for gardeners with small compost heaps, because it can be easily stored, is pleasant to handle, and is less costly than other forms of bagged organic nitrogen.

Hops

Hops are viny plants grown and used for making beer. (Hops impart the characteristic bitter flavor.) Spent hops, the wastes left after the brewing process, are an excellent garden fertilizer, containing (when dry) 2.5 to 3.5 percent nitrogen and 1 percent phosphoric acid. They do have a strong odor when wet and fresh, but this dissipates rapidly.

Wet hops may be spread directly on the garden in fall or spring just as you would apply manure. Turn the matter under, mixing it with the top 4 to 5 inches of soil. Wet hops heat up rapidly, so keep them several inches away from plant stems to burning. This tendency to heat up is, of course, desirable in making compost. Be sure to balance the sogginess of spent hops with absorbent matter.

Spent hops make a good mulch when dry. They resist blowing away and will not easily ignite if a lighted match is tossed onto a pile. (Many other mulch materials burn easily.) A layer of dry, spent hops will break down slowly, staying put for 3 years or more.

Another brewery waste to inquire about is the grain left over from the mashing process. When wet, this material contains almost 1 percent nitrogen and decays rapidly. Brewers’ grains are also in high demand for livestock feed.

Incinerator Ash

Incinerator ash, if available, can be a fine source of phosphorus and potash for the compost heap. Its phosphorus content depends upon what was burned but averages 5 or 6 percent; its potassium content is from 2 to 3 percent. As with many compostable materials, the source of the ash should be considered before it is added to the compost pile. Ash from apartment-building incinerators may be acceptable, depending on the materials burned. It is best to avoid municipal incinerator ash, most of which is considered hazardous waste because the heavy metals and other toxic substances found in municipal solid waste often become more concentrated and soluble when burned.

Leather Dust

Available as a by-product of leather processing and as a commercial fertilizer from garden shops, leather dust contains from 5.5 to 12 percent nitrogen. Phosphorus is also present in considerable amounts.

Leather dust is often contaminated with the heavy metal chromium, used in the tanning process, and is for this reason prohibited for use by organic farmers. Unless you have a source that produces leather dust with low or no levels of heavy-metal contaminants, it is best to refrain from using it on your compost or on soil in which food crops will be grown.

Leaves

Leaves are a valuable compostable and mulch material abundantly available to most gardeners. Because trees have extensive root systems, they draw nutrients up from deep within the subsoil. Much of this mineral bounty is passed into the leaves, making them a superior garden resource. (See the table “Composition of Fallen Leaves” on this page.) Pound for pound, the leaves of most trees contain twice the mineral content of manure. The considerable fiber content of leaves aids in improving the aeration and crumb structure of most soils.

Many people shy away from using leaves in compost because they’ve had trouble with them packing down and resisting decay. Leaves don’t contain much nitrogen, so a pile of them all alone may take years to decay fully. But most leaves can be converted to a fine-textured humus in several weeks (or, at most, a few months) if some general guidelines are followed.

• Add extra nitrogen to your leaf compost since leaves alone don’t contain enough nitrogen to provide sufficient food for bacteria. Manure is the best nitrogen supplement, and a mixture of five parts leaves to one part manure will break down quickly. If you don’t have manure, nitrogen supplements like dried blood, alfalfa meal, and bonemeal will work almost as well. In general, add 2 cups of dried blood or other natural nitrogen supplement to each wheelbarrow load of leaves.

• Don’t let your leaves sit around too long and dry out. As leaves weather, they lose whatever nitrogen content they may have had. This, combined with the dehydration of the cells, makes them much more resistant to decomposition than when used fresh.

• Grind or shred your leaves. A compost pile made of shredded material is easily controlled and easy to handle.

If you don’t have a shredder, you can adapt various other devices to leaf shredding. Many people use a rotary mower for shredding. A mower that is not self-propelled is best and easiest to control. Two people can work together very nicely, one piling up leaves in front of the mower and the other running it back and forth over the pile. A leaf-mulching attachment on the blade will cut the leaves more finely, but sometimes it is not necessary. You will be surprised how many leaves you can shred this way in 30 minutes or so.

Of course, some people use a mower with a mulching attachment to cut up leaves right on the lawn. This does not make them available for compost or mulch somewhere else—like the garden—where they are more essential.

If you have so many leaves that you can’t compost all of them—or if you don’t have the time to make compost—you can make leaf mold. Leaf mold is not as rich a fertilizer as composted leaves, but it’s easier to make and is especially useful as mulch.

A length of snow fencing or woven wire fencing placed in a circle makes the best kind of enclosure for making leaf mold. Gather leaves in the fall and wet them thoroughly; then tamp them down in the enclosure. Leaves are slightly acid. If your plants don’t need an acid mulch, add some limestone to the leaves before tamping them down.

These leaves will not break down over the winter into the kind of black, powdery leaf mold found on the forest floor, but by spring or summer they will be broken up enough to serve as a fine mulch. Some people, including nursery operators who require fine potting soil, keep leaves “in cold storage” for several years. When they come for their leaves, they find black, crumbly humus.

Leaf mold is ordinarily found in the forest in a layer just above the mineral soil. It has the merit of decomposing slowly, furnishing plant nutrients gradually, and improving the soil structure as it does so. Leaf mold’s ability to retain moisture is amazing. Subsoil can hold a mere 20 percent of its weight in water; good, rich topsoil will hold 60 percent; but leaf mold can retain 300 to 500 percent of its weight.

Freshly fallen leaves pass through several stages, from surface litter to well-decomposed humus partly mixed with mineral soil. Leaf mold from deciduous trees is somewhat richer in such mineral foods as potash and phosphorus than that from conifers. The nitrogen content varies from 0.2 to 5 percent.

If you keep poultry or livestock, use your supply of leaves for litter or bedding along with straw or hay. Leaf mold thus enriched with extra nitrogen may later be mixed directly with soil or added to the compost pile.

A lawn sweeper is a good tool to use for collecting leaves. It is easier than raking and often does a better job. Handheld leaf vacuums are also available at most lawn and garden stores.

Many municipalities are now composting leaves and yard wastes instead of dumping them into landfills. If your community has such a program, you can send in your surplus leaves with a good conscience and probably pick up finished compost in return.

Limestone

Limestone is an important source of calcium and, when dolomitic limestone is used, magnesium. It is commonly applied to raise the pH of acidic soils and may sometimes be appropriate when composting very acidic materials such as pine needles. However, compost made from a good variety of materials should have a pH near neutral without the addition of lime. Moreover, it is unwise to use lime with fresh manure or other nitrogenous materials, as it reacts chemically to drive off ammonia gas and thus loses some of the valuable nitrogen.

If your soil is acidic, it is best to apply lime to it directly, rather than through compost. Any reliable soil test will tell you how much lime is needed. If you live in a humid region, lime should be applied every 3 or 4 years, preferably in the fall so it will become available first thing in the spring. Use a grade fine enough to pass through a 100-mesh screen. In drier climates, where soil pH is naturally neutral or higher, liming is rarely necessary. You may want to use some lime for making potting soil with your compost—use about 1 tablespoon for 20 quarts of soil mix.

Most vegetables and garden plants prefer a slightly acidic to neutral pH, so laboratory liming recommendations generally strive for a pH of 6.5 to 6.8 (a pH of 7 is neutral). Some vegetables—legumes such as beans, peas, and alfalfa, for example—do better with slightly alkaline soil, while many berries prefer acidic conditions. Organic matter in the soil tends to buffer the effects of pH extremes by making nutrients available to plants regardless of soil pH. Lime, therefore, should be used to supplement soil improvement through the addition of compost.

Manure

Manure is the most valuable ingredient in the compost pile. For a full discussion of using manure in composting, see Chapter 7.

Molasses Residues

The wastes from sugar refining are obviously rich in carbohydrates, but they also contain some mineral nutrients. Naturally occurring yeasts in the compost will ferment these sugars rapidly. Dry molasses is often available from feedstores.

Olive Wastes

Olive pits contain phosphorus, nitrogen, and some lignin (a woody substance related to cellulose). But the pits must be ground or chopped before composting, or they’ll take years to decay. Pulpy olive wastes vary in nutrient density. One analysis showed the pomace (what’s left after oil extraction) having 1.15 percent nitrogen, 0.78 percent phosphoric acid, and 1.26 percent potassium. The pulp is oily and should be well mixed with other organic matter.

Paper

Many kinds of paper, even those with colored inks, can be used for compost or mulch. You can save a lot on trash collection costs, and keep the valuable carbon for your soil, by recycling paper through your compost. Although the colored inks contain various heavy metals, one study found that their concentration is low enough to be negligible, even when glossy magazines are used as a garden mulch. If only a few colored-ink items are mixed in with newsprint, there should be no cause for concern.

The secret to using paper successfully is to shred or chop it as finely as possible. Matted layers of newspaper, like hay and grass clippings, will halt the composting organisms in their tracks. Various tools will work for this process, including shredders used for brush. If you don’t have a lot of paper, a sharp machete will chop it adequately. And don’t forget the office paper shredder—you may even be able to recycle preshredded office paper from local businesses. Dairy farmers in various regions are being encouraged to use newspaper, which they shred using silage-making equipment, as bedding for their animals. The newspaper is very absorbent and makes an excellent compost medium when mixed with manure.

Shredded paper should be incorporated into your compost in layers, alternating with garbage or other wet materials. Because it is almost pure cellulose, it requires a concentrated nitrogen source to stimulate decomposition, but once broken down it creates a high-quality humus that will improve the tilth of any soil.

Peat Moss

This naturally occurring fibrous material is the centuries-old, partially decayed residue of plants. Widely sold as a soil conditioner, mulch, and plant propagation medium, peat’s major advantages are its water retention (it is capable of absorbing 15 times its weight in water) and fibrous bulk. Dry peat will help loosen heavy soils, bind light ones, hold nutrients in place, and increase aeration. But while its physical effects on soil are valuable, peat isn’t a substitute for compost or leaf mold. Expensive, relatively low in nutrients, and acidic, peat is best used as a seed-flat and rooting medium or as a mulch or soil amendment for acid-loving plants.

If a distinctly acidic compost is needed for certain plants, substitute peat for the soil in your compost pile. (See “Soil,” this page.) Peat compost is beneficial for camellia, rhododendron, azalea, blueberry, sweet potato, watermelon, eggplant, potato, and tomato plants—all of which prefer acidic soil conditions.

Pea Wastes

Feeding pea shells and vines to livestock and getting the waste back as manure is an excellent recycling method. Otherwise, pea wastes can be rapidly composted since they are rich in nitrogen when green. Dry vines should be shredded or chopped before or during composting, to hasten decay. Diseased vines should be burned and the ashes returned to the soil. (Pea ash contains almost 3 percent phosphoric acid and 27 percent potassium.)

Pet Wastes

As discussed earlier in this chapter, the wastes of dogs, cats, and birds are potential carriers of organisms that may cause disease in humans. Such materials should not be included in the home compost pile. Wastewater from aquariums, however, contains a certain amount of algae and organic matter that can be beneficial to plants. Use aquarium water to add moisture to your compost heap or for watering plants.

Phosphate Rock

Phosphate rock is a mainstay in organic gardens and farms because of its value as a soil and compost pile amendment. While its chemical composition varies according to the source, phosphate rock generally contains 65 percent calcium phosphate or bone phosphate of lime. A diversity of other compounds and micronutrients important to plant development is also present.

Phosphate rock is a naturally occurring mineral, however; don’t confuse it with superphosphate. The latter has been treated with sulfuric acid to increase its solubility. But many micronutrients are lost due to this processing, and the increase in the availability of sulfur stimulates the presence of sulfur-reducing bacteria in the soil. These organisms attack sulfur and also ingest a fungus that normally breaks down cellulose in the soil. Besides encouraging this microbial imbalance, superphosphate can leave harmful salts in the soil. Furthermore, within a few days superphosphate will react chemically with calcium and other soil nutrients to become indistinguishable from the less-soluble rock powder.

Phosphate rock creates no such problems. It’s slow acting, which makes nutrients available to plants for many years after a single application. Applied alone to vegetable or flower gardens, 1 pound to every 10 square feet of growing area will suffice for 3 to 5 years. It may be sprinkled lightly over succeeding layers in a compost heap to add nutrients to the finished product. It is valuable when combined with manure and other nitrogenous materials, since it prevents loss of nitrogen in the form of ammonia. The nutrients in rock phosphate are more readily available to plants when it is added via compost, having first been incorporated into the bodies of countless microorganisms.

Worldwide phosphate deposits are rapidly being depleted, and some experts suggest that we are in a time of “peak phosphorus.” For this reason, it is best to look toward recycling of phosphorus through the return of organic wastes and manure to the soil. Phosphorus runoff from farm fields poses a similar threat to nitrogen runoff, causing algae blooms and other problems in surface waters. By encouraging high fungal soil organisms and stimulating mycorrhizal growth in your compost, you can maintain adequate phosphate nutrition for crops without contributing to extraction of an increasingly scarce resource.

Pine Needles

Pine needles are compostable, although they will break down rather slowly because of their thick outer coating of a waxy substance called cutin. Pine needles are also acidic in nature, and for this reason they should not be used in large quantities, unless compost for acid-loving plants is desired. For best results, shred the needles before adding them to the heap.

Evergreen needles have been found to be effective in controlling some harmful soil fungi, such as Fusarium spp., when used as a mulch or mixed directly into the soil.

Potato Wastes

Potato peels are common components of kitchen scraps. They provide a valuable source of nitrogen (about 0.6 percent as ash) and minor elements for the compost pile. Rotted whole potatoes, chopped or shredded, are worthwhile compost pile additions. The tubers contain about 2.5 percent potash, plus other minerals. Use the potato vines, too; they can be either composted or dug back into the soil. The vines, when dry, contain approximately 1.6 percent potash, 4 percent calcium, and 1.1 percent magnesium, plus sulfur and other minerals.

Rice Hulls

Often considered a waste product, rice hulls have been found to be rich in potash and to decompose readily, increasing humus content, when worked into the soil. The hulls make an excellent soil conditioner and a worthwhile addition to the compost heap. They also make a good, long-lasting mulch that does not blow away.

Gardeners in the Texas–Louisiana Gulf Coast area can often get ample amounts of this material from rice mills; occasionally it is free. Some mills make a practice of burning the hulls, and the residue from this operation contains a high percentage of potash, making it especially valuable as a composting material.

Sawdust

Sawdust is often useful in the compost heap, although it is better used as a mulch. Some gardeners who have access to large quantities use it for both, with equally fine results. In most areas, lumberyards will occasionally give sawdust free for the hauling. Sawdust is very low in nitrogen. One of the objections against using sawdust is that it may cause a nitrogen deficiency. However, many gardeners report fine results from applying sawdust as a mulch to the soil surface without adding any supplementary nitrogen fertilizer. If your soil is of low fertility, watch plants carefully during the growing season. If they become light green or yellowish in color, side-dress with an organic nitrogen fertilizer such as alfalfa meal, bloodmeal, compost, or manure. Regular applications of manure tea will also counteract any slight nitrogen deficit.

Some people are afraid that the continued application of sawdust will sour their soil—that is, make it too acidic. A comprehensive study made from 1949 to 1954 by the Connecticut Agricultural Experiment Station of sawdust and wood chips reported no instance of sawdust making the soil more acidic. It is possible, though, that sawdust used on the highly alkaline soils of the western United States would help to make the soil neutral, a welcome effect.

When used for compost, sawdust is valuable not only as a carbon source but as a bulking agent, allowing good air penetration in the pile. This is true only of sawdust that comes from sawmills or chain saws; the fine material that results from sanding can become packed and anaerobic. Although sawdust is slow to break down, the larger bits you may find remaining in finished compost will not present problems when added to your soil and will improve the texture of heavy soils. Wood wastes such as sawdust also stimulate fungal colonization, helping to extract phosphorus from otherwise unavailable soil reserves.

Seaweed

Coastal gardeners can gather different types of seaweed by wandering the shoreline. Look for kelp (laminaria), bladder wrack (also called fucus), sea lettuce (ulva), and other varieties. Gardeners elsewhere can buy dried, granulated seaweed (kelp meal) or liquid concentrate. All these seaweed variants are rich in many types of micronutrients and are a boon to plants, soil health, and the compost pile.

Compared with barnyard manure, seaweed in general has a similar organic content. The proportions, however, vary—seaweed has more potassium than manure but has less nitrogen and phosphorus. Seaweed is perhaps most valued for its micronutrient content. An analysis of the seaweed most commonly used in seaweed meals and extracts identified the presence of some 60 elements, including all those important for plant, animal, and human health.

Use wet, fresh seaweed quickly because it deteriorates rapidly when piled haphazardly. Exposure to the elements will quickly leach out many of seaweed’s soluble minerals. Dig the seaweed under, or mix it with nitrogenous and absorbent materials for rapid composting. Bacteria feast on the alginic acid found in the leaves, which makes seaweed an excellent compost pile activator. If composted with manure that is rich in litter, seaweed aids the speedy decay of the straw; very little nitrogen is lost, and all the other elements are preserved. Decay occurs rapidly.

If you have only a small amount of seaweed, chop it and soak it overnight in a gallon of hot water (160° to 180°F/71° to 82°C). Sprinkle this mixture over successive layers of the compost pile. The liquid can also be used as a fertilizer and as a seed-soaking solution.

Kelp meal can be used as an activator in compost, since its rich micronutrient composition stimulates microbial growth. Seaweed extract can be used to feed plants directly through their leaves, and may also be applied to compost in the course of moistening the layers. When used as a foliar feed, plant growth is also stimulated by seaweed’s content of cytokinins and other plant growth hormones.

Sewage Sludge

Sewage sludge is the solid residue left after organic wastes and wastewater have been chemically, bacterially, or physically processed. Depending on how it is processed, sludge may contain up to 6 percent nitrogen and from 3 to 6 percent phosphorus.

Activated sludge is produced when sewage is agitated by air rapidly bubbling through it. Certain types of very active bacteria coagulate the organic matter, which settles out, leaving a clear liquid that can be discharged with a minimum amount of pollution. The resulting sludge is usually heat-treated before being offered as a soil amendment.

Digested sludge is formed when the solid matter in sewage is allowed to settle without air agitation, the liquid is drained off, and the sludge is fermented anaerobically. The conventional anaerobic digestion system takes from 15 to 30 days at 99°F (37°C) from the time the sewage reaches the sedimentation tank until the digested solids are pumped into filter beds for drying. The dried material is either incinerated or used for soil improvement.

Until recently, most sewage sludge was incinerated, buried in landfills, or dumped offshore. Now there’s an increasing interest in using this potentially valuable material as a soil conditioner. This would be ideal if the residue were composed solely of the remains of human waste, but that isn’t the case. Since industrial wastes are often treated in the same sewage plants as household wastes, sewage sludges are often contaminated with heavy metals that, when regularly incorporated into the soil, can build up to toxic levels.

All municipal sludge must be composted at high temperatures before it can be safely used as a garden fertilizer. Even then, avoid using it for edible crops, especially roots and leafy greens, since some viruses can survive hot composting temperatures. Any municipal solid-waste composting operation should provide information on metals and other toxic compounds in its products if it offers them for sale to the public; most states prohibit distribution of uncomposted sludge to the public.

As restrictions on sewage waste disposal make it more difficult and costly, an increasing number of cities are establishing sludge composting programs. Gardeners who have access to the products of such programs should ask questions and get detailed answers about the content of the sludge, its chemical analysis, and how it has been processed. Unless you’re absolutely sure of the chemical content of your community’s sludge, don’t apply it near or on food crops or anywhere that runoff might contaminate a garden, an orchard, or a well. See Chapter 13 for more information about municipal sludge composting.

Sewage sludge, composted or not, is prohibited for use as a fertilizer by organic farmers. See Chapters 8 and 12 for discussions of the rules governing compost and other permitted fertility inputs for organic farming under the USDA’s National Organic Program.

Soil

While not a necessity, soil is a valuable component in compost making. The thin (⅛-inch) layer called for in Indore heaps contains billions of soil organisms that consume plant, animal, and mineral matter, converting it to humus. Soil also contains minerals and organic matter, so it acts like an activator when added to compostables. You can achieve much the same results using finished compost saved from a previous batch.

Thin layers of dirt in the compost heap work to absorb unstable substances produced by fermentation, thereby slowing their loss to the atmosphere. And when the pile is built, a topping of several inches of topsoil will stop heat and water from leaving the pile. Don’t add too much soil, however, or the finished compost will be quite heavy.

Other than your own property, sources for soil include nearby woods, fields, building excavations, and mud from streams and ponds free of industrial or agricultural pollution. Don’t use pond or stream mud directly in your soil; it will have the same effect as adding raw manure. Mud is also easier to handle if you dry it before composting, by mixing it with layers of absorbent plant wastes.

Straw

Although straw will add few nutrients to the compost heap, it is widely used because it is readily available and adds considerable organic material. It is unsurpassed as an aerating medium, as each straw acts as a conduit for air to circulate throughout the pile.

The fertilizer value of straw is, like that of all organic matter, twofold: It adds carbon material and plant food to the compost. The carbon serves the soil bacteria as energy food, while the plant food becomes released for growing crops. Where straw is used as mulch, incorporate considerable amounts of nitrogen (preferably in the form of manures) so that the bacteria that break down the straw into humus do not deplete the soil of the nitrogen needed by growing plants.

If used in quantity, the straw should be cut up. Long pieces of straw mixed with other materials that hold water or composted with ample amounts of barnyard manure offer no trouble, though heaps cannot be turned easily. Straw compost must therefore be allowed to stand longer. For quicker compost, weigh down the material with a thicker layer of earth. This also preserves the moisture inside the heap.

If a large straw pile is allowed to stay outside in the field, it will eventually decay at the bottom into a crumbly substance. Such material is excellent for compost making and mulching. Some of the fungi it contains are of the types that form mycorrhizal relations with the roots of fruit trees, evergreens, grapes, roses, and so on, and a straw mulch will therefore benefit these plants not only as a moisture preserver but as an inoculant for mycorrhizae.

The nitrogen value of straw is so small that it need not be accounted for in composting. The mineral value of straw depends on the soils where the crops were grown. (See the table “Typical Analyses of Straws” on this page.)

Sugar Wastes

The most plentiful sugar-processing residue is burned bone, or bone charcoal, which is used as a filtration medium. Called “bone black” when saturated with sugar residues, this substance contains 2 percent nitrogen, more than 30 percent phosphorus, and a variable potassium content. Raw sugar residues, also known as bagasse, have over 1 percent nitrogen and over 8 percent phosphoric acid.

Tanbark

Tanbark is plant waste that remains following the tanning of leather. Its residues are shredded, heaped, and inoculated with decay-promoting bacteria. Thus composted, tanbark is sold in bulk as mulching material. Analysis shows nitrogen at 1.7 percent, phosphorus at 0.9 percent, and potassium at 0.2 percent; minor amounts of aluminum, calcium, cobalt, copper, iron, lead, magnesium, molybdenum, zinc, and boron are also present. Like peat, tanbark makes an excellent mulch but is generally too expensive to use extensively in compost.

TYPICAL ANALYSES OF STRAWS (%)

Tankage

Tankage is the refuse from slaughterhouses and butcher shops, except blood freed from the fats by processing. Depending on the amount of bone present, the phosphorus content varies greatly. The nitrogen content varies usually between 5 and 12.5 percent; the phosphoric acid content is usually around 2 percent, but may be much higher.

Tankage, because it is usually rich in nutrient value, is especially valuable to the compost pile. However, it is also in demand as a feed additive and so is available only sporadically. Because it is an animal waste, tankage does require special care in composting. Your compost must be kept in a secure, enclosed container, safe from four-legged scavengers. Use a good supply of high-carbon materials such as leaves, hay, or sawdust to absorb odors, with a layer of soil over each layer of tankage.

Tea Grounds

Useful as a mulch or for adding to the compost heap, one analysis of tea leaves showed the relatively high content of 4.15 percent nitrogen, which seems exceptional. Both phosphorus and potash were present in amounts below 1 percent.

Tobacco Wastes

Tobacco stems, leaf waste, and dust are good organic fertilizer, especially high in potash. The nutrients contained in 100 pounds of tobacco wastes are 2.5 to 3.7 pounds of nitrogen, almost 1 pound of phosphoric acid, and from 4.5 to 7 pounds of potassium.

Tobacco leaves are “stripped” for market in late fall, leaving thousands of stalks. Some farmers use their stalks to fertilize their own fields, chopping up the stalks and disking them into the soil. Some stalks are available for gardeners, however, and tobacco processing plants bale further wastes for home use.

These wastes can be used anywhere barnyard manure is recommended, except on tobacco, tomatoes, potatoes, and peppers because they may carry some of the virus diseases of these crops, especially tobacco mosaic virus.

Compost tobacco wastes, or use them in moderation in mulching or sheet composting mixed with other organic materials. They should not be applied alone in concentrated amounts as a mulch—the nicotine will eliminate beneficial insects, earthworms, and other soil organisms as well as harmful ones.

Water Hyacinth

Southerners who lack sufficient green matter for compost can often find quantities of the water hyacinth (Eichhornia crassipes) growing in profusion in Southern streams. This plant is considered a serious menace to agriculture, fisheries, sanitation, and health in the South and other parts of the world where it grows with remarkable rankness. For best results, shred and mix it with partially decomposed “starter material” such as soil or manure.

Weeds

Weeds can be put to use in the compost pile. Their nitrogen, phosphorus, and potash content is similar to other plant residues, and large quantities can provide much humus for the soil. Weed seeds will be killed by the high temperatures in the compost pile, and any weeds that sprout from the top of the heap can be turned under. Be careful not to allow weeds to grow and set seed on your finished compost. Weeds can even be used for green manure, as long as they will not be stealing needed plant food and moisture. Some produce creditable amounts of humus, make minerals available, and conserve nitrogen.

There are certain weeds that you are better off burning or piling separately from your garden compost, since they are extremely vigorous and hard to kill. This applies primarily to weeds that reproduce through underground stems or rhizomes, such as quack grass, johnsongrass, bittersweet, and bishop’s-weed.

Wood Ash

Wood ash is a valuable source of potash for the compost heap. Hardwood ashes generally contain from 1 to 10 percent potash, in addition to 35 percent calcium and 1.5 percent phosphorus. Wood ashes should never be allowed to stand in the rain, as the potash would leach away. Use wood ashes cautiously—it is not uncommon for home gardeners to create difficult nutrient imbalance problems by applying too much wood ash. It is a strong alkalinizing agent and also increases soil salinity. You should use it in the garden only if a soil test indicates acidic soil and a lack of potassium.

Wood ashes can be mixed with other fertilizing materials or side-dressed around growing plants. Apply no more than 2 pounds per 100 square feet. Avoid contact between freshly spread ashes and germinating seeds or new plant roots by spreading ashes a few inches from plants. Be similarly sparing with wood ashes in your compost—use no more than a dusting on each layer, if you must. Manure and hay are also rich in potassium, and they do not pose the dangers of wood ashes.

Wood Chips

Like sawdust and other wood wastes, wood chips are useful in the garden. In some ways, wood chips are superior to sawdust. They contain a much greater percentage of bark and have a higher nutrient content. Since they break down very slowly, their high carbon content is less likely to create depressed nitrogen levels. They do a fine job of aerating the soil and increasing its moisture-holding capacity, and they make a fine mulch for ornamentals. Wood chips promote fungal growth, including mycorrhizae, which improves stable humus, aggregation, and the water-holding capacity of your soil.

Generally, the incorporation of fresh chips has no detrimental effect on the crop if sufficient nitrogen is present or provided. Better yet, apply the chips ahead of a green manure crop, preferably a legume; allow about a year’s interval between application and seeding or planting of the main crop. Other good ways to use wood fragments are as bedding in the barn, followed by field application of the manure; as a mulch on row crops, with the partially decomposed material eventually worked into the soil; and adequately composted with other organic materials. Well-rotted chips or sawdust are safe materials to use under almost any condition.

Wool Wastes

Wool wastes, also known as shoddy, have been used by British farmers living in the vicinity of wool textile mills since the industrial revolution in the early 19th century. The wool fiber decomposes when in contact with moisture in the soil and, in the process, produces available nitrogen for plant growth. Generally, the moisture content of the wool wastes is between 15 and 20 percent. It contains from 3.5 to 6 percent nitrogen, 2 to 4 percent phosphoric acid, and 1 to 3.5 percent potash.

C/N RATIOS AND NUTRIENT ANALYSES

The following tables and lists provide information about the carbon/nitrogen ratios and relative nutrient contents of a variety of organic materials. The presence of a material in this section does not necessarily mean it is ideal for composting; neither does exclusion of a material mean that it cannot be composted. As mentioned at the beginning of this chapter, the best materials for composting may be those that are in close proximity to the compost pile.

Many items are listed as ash; however, it is not recommended to reduce organic matter to ash. These materials are most valuable as compost pile additions in their natural conditions. Burning organic matter also eliminates moisture, and the carbon it contains is sent into the atmosphere instead of feeding soil life. The only organic matter you should consider burning would be diseased plant materials or noxious weeds. Be aware that most municipalities place restrictions on burning, especially at certain times of the year.

Since nearly all organic material contains some amount of nitrogen, phosphorus, potassium, and micronutrients, you don’t need to obsess over including all the plant nutrients in your compost pile. If you incorporate a good variety of materials into your compost, the necessary nutrients will be there. As mentioned in Chapter 4, compost not only provides nutrients, it also makes soil nutrients more available to plants. Only in instances where soil analysis indicates a significant nutrient deficiency should much effort be given to boosting levels of a certain nutrient in your compost.

CARBON/NITROGEN RATIOS OF BULKY ORGANIC MATERIALS

For discussion of carbon/nitrogen ratios in composting, see Chapter 8.

Natural Sources of Nitrogen

The materials listed below are grouped into representative classifications of organic matter; each group is ordered from highest nitrogen concentration to lowest. For specific nitrogen analyses, see the table “Percentage Composition of Various Materials” starting on this page.

Manure

Rabbit manure	Swine manure
Sewage sludge	Sheep manure
Chicken manure	Horse manure
Human urine	Cattle manure

Animal Wastes (other than manures)

Feathers	Fish (dried, ground)
Felt wastes	Wool wastes
Dried blood	Jellyfish (dried)
Crabs (dried, ground)	Lobster refuse
Silkworm cocoons	Shrimp wastes
Fish scraps (fresh)	Mussels
Tankage	Eggshells
Silk wastes	Milk
Shrimp heads (dried)	Oyster shells
Crabs (fresh)

Meal

Cottonseed meal	Bonemeal (steamed)
Gluten meal	Bone black
Bonemeal (raw)	Oats (green fodder)
Wheat bran	Corn silage

Plant Wastes

Tung oil pomace	Tobacco stems
Castor pomace	Coffee grounds
Tea grounds	Sugar wastes
Peanut shells	Seaweed (dried)

Plant Wastes

Olive pomace	Potato skins (raw)
Brewery wastes	Pine needles
Cocoa shell dust	Beet wastes
Grape pomace	Seaweed (fresh)

Leaves

Raspberry leaves	Pear leaves
Apple leaves	Cherry leaves
Peach leaves	Grape leaves
Oak leaves	Pea (garden) vines

Grasses

Cowpea hay	Soybean hay
Vetch hay	Pea forage
Alfalfa	Timothy hay
Red clover	Salt marsh hay
Clover	Kentucky bluegrass hay
Millet hay	Immature grass

Natural Sources of Phosphate (other than phosphate rock or bonemeal)

The following phosphate sources are listed in order from highest phosphorus content to lowest. For specific phosphorus analyses, see the table “Percentage Composition of Various Materials” starting on this page.

Shrimp wastes	Tankage
Sugar wastes (raw)	Castor pomace
Fish (dried, ground)	Rapeseed meal
Sludge (activated)	Wood ashes
Lobster and crab refuse	Cocoa shell dust
Wool wastes	Chicken manure
Dried blood	Rabbit manure
Banana residues (ash)	Silk mill wastes
Apple skins (ash)	Sheep and goat manure
Orange skins (ash)	Swine manure
Peapods (ash)	Horse manure
Cottonseed meal	Cattle manure
Hoof and horn meal

Natural Sources of Potash

The materials in each group below are listed in order from highest potassium content to lowest. For specific potash analyses, see the table “Percentage Composition of Various Materials” starting on this page.

Natural Minerals

Greensand	Basalt rock
Granite dust

Hay Materials

Millet hay	Pea forage
Cowpea hay	Timothy hay
Vetch hay	Winter rye
Soybean hay	Immature grass
Alfalfa hay	Salt marsh hay
Red clover hay	Pea (garden) vines
Kentucky bluegrass hay

Straw

Buckwheat straw	Sorghum straw
Oat straw	Cornstalks
Barley straw	Wheat straw
Rye straw

Leaves

Cherry leaves	Grape leaves
Peach leaves	Pear leaves
Raspberry leaves	Oak leaves
Apple leaves

Manure

Pigeon manure	Duck manure
Chicken manure	Rabbit manure
Swine manure	Sheep or goat manure
Horse manure	Cattle manure

Miscellaneous

Banana residues (ash)	Wool wastes
Peapods (ash)	Rapeseed meal
Cantaloupe rinds (ash)	Beet wastes
Wood ash	Castor pomace
Tobacco stems	Cottonseed meal
Cattail reeds or water lily stems	Potato vines (dried)
Molasses wastes	Vegetable wastes
Cocoa shell dust	Olive pomace
Potato tubers	Silk mill wastes

PERCENTAGE COMPOSITION OF VARIOUS MATERIALS

The presence of a C, N, or O in the C/N column indicates whether a material’s effect on compost would be carbonaceous (C), nitrogenous (N), or other (O). Rock powders, for example, do not affect the C/N ratio and are designated O. C/N ratios of ashed materials represent their effects when fresh; when ashed, they are similar to rock powders.