A L A B A M A A & M A N D A U B U R N U N I V E R S I T I E S Backyard ANR-638 Composting wenty percent of the 2.6 million tonsT of solid waste produced annually in Alabama is composed of lawn and gar-den wastes such as grass clippings, shrub- THE COMPOST ENVIRONMENTbery trimmings, leaves, tree prunings, homegarden refuse, and kitchen wastes. The quan- For efﬁcient and rapid composting, thetity of these wastes is exceeded only by microorganisms that do the work need topaper and paperboard waste products. have the right balance of air, water, carbon, nitrogen, and temperature. The magnitude of solid waste productionis presenting disposal problems insanitary landﬁlls. Many landﬁlls Compost pile.have been forced to close as aresult of being full or en-vironmentally un-sound. The scope ofthe disposal prob-lem could besigniﬁcantlyreducedthrough com-posting. The key to ef-fective compost-ing in the homelandscape is toregulate theconditionsunder whichmicrobial de- Composting cagecomposition made of concrete 3-Bin composting unit. reinforcing wire.takes place. As thesuccessful gardener controls the factors thatpromote plant growth and development, the Airsuccessful composter controls the conditions Composting is an aerobic process, whichthat encourage microorganisms to decom- means it occurs in the presence of oxygen.pose plants and other organic wastes efﬁ- The compost pile gets oxygen two ways: (1)ciently. Keep in mind that composting is the by the turning of compost; and (2) by build-compressing of a process that could take ing the pile so surface air can diffuse into theyears to occur in nature into a period of center. When a pile gets too little oxygen, itmonths or even weeks in the home yard or will become anaerobic, and offensive odorsgarden. can result. Visit our Web site at: www.aces.edu
he word compost is derived from T two Latin words meaning, “together” and “to bring.” In one sense, it involves bringing together waste materials to ultimately form a single uniform humus. In the technical sense, composting results in the microbial decomposition of organic wastes under controlled conditions.Backyard W ater is needed for the microor- ganisms that T he 130°F to 150°F temperatures gen- erated in the core decompose waste to grow of a compost pile is ade- and multiply. A handful quate to kill most weed of compost should feel seeds and many patho- like a wrung-out sponge. genic organisms. Squeeze it and no more than a drop or two should come out. C ompost is “ﬁnished” or “stable”—ready toI n Alabama, a family of four generates an average use—when most of the of 2.5 tons of garbage per original plant materials areyear. Nearly a half ton of that not recognizable. Finishedgarbage is yard waste that can compost is dark colored,be composted. crumbly, and looks and feels like soil. Y ard wastes—grass clippings, leaves, weeds, and prunings less than 6 inches in diameter from residences or businesses.
F inished compost contains nitrogen, phosphorus, and potassium, although the amount of each element varies. Most of the nitrogen and phos- phorus are present in an organ- ic form, and they are releasedA eration— contact gradually. That makes compost with air a good slow-release fertilizer forby turning so trees and shrubs. Generally, ad-microbial aero-bic metabolism ditional fertilizer will have totakes place. be added for vegetables and bedding plants.CompostinCompostiC omposting L eachate— liquid that drains from DON’T A tools are the mix of fresh 1,000-square-foot designed to organic matter. area of lawn can compost fats: butter,penetrate the pile generate up to 500 bones, cheese, chicken,and open up a passage pounds of grass clippings ﬁsh, lard, mayonnaise,for air and moisture in a single growing season. meat, milk, peanutwhen withdrawn. butter, salad dressing,Tools are available sour cream, vegetablefrom seed and garden oil, yogurt . . . .product suppliers. P athogen— any disease- producing microorganism.
B iodegradability—the potential for being converted into simpler structures.S awdust will C ompost tilled decompose very into a sandy soil improves slowly unless the soil’s capacitynitrogen is added. to hold water andAdd 3.5 pounds of nutrients. Addedactual nitrogen to to a heavy clay soil,each cubic yard of compost increases the air spaces be-sawdust, or add 11 tween clay particles,pounds of ammonium which improvesnitrate. drainage and in-ng creases soil aera- tion. In either soil extreme plants are beneﬁted. C ompost kitchen scraps, includ- ing apples, cabbage, carrots, cel- ery, coffee grounds, egg shells, grapefruit, lettuce, onions, oranges, pears, pineapple, potatoes, pumpkins, squash, tomatoes, turnips—just about any vegetable waste. 4
grass clippings, or manure should be addedWater at the same time. Microorganisms need water to survive Surface area is important in this relation-and function. Ideally, the moisture content of ship because carbon in leaves is much morethe compost pile should be between 40 and available than the carbon in a large wood60 percent. The compost should be moist chip. Small chips give the microorganismswhen squeezed but not dripping wet. If too more surface area on which to feed. A leafwet, the decomposition process will slow shredder or chipper is useful equipment fordown. preparing an efﬁcient compost pile.Carbon And Nitrogen Temperature The microorganisms that do the compost- As the microorganisms grow and multi-ing need food. They get energy from materi- ply, they generate heat from metabolism.als high in carbon (carbohydrates such as cel- Heat is beneﬁcial in that it destroys manylulose, lignin, and complex sugars in plant kinds of weed seed and diseaseresidues.) organisms; how-They also ever, when tem-need protein, peratures risewhich they above 140°F, themanufacture beneﬁcial mi-from materials croorganismshigh in nitro- start to die.gen (manures, Turning the pilekitchen scraps, when tempera-and fertilizer tures reach thisnitrogen). point will pre- The ratio vent overheatingof carbon (C) and will speedto nitrogen (N) up the entireis important. process.If there is toolittle N, themicrobial pop-ulation willnot grow to anoptimum size,and decompositionwill slow down. On the otherhand, while too much N compared to C al-lows rapid microbial growth and speeds updecomposition, it can result in depleted oxy-gen and odors as the excess N is given off asammonia gas. The optimum C:N ratio isabout 30:1. If materials added to the pile havea high C:N ratio, then some Nshould be added to more closelyapproximate an optimumC:N ratio. For example, ifsawdust is placed in the pile,then some N fertilizer, Grass Clippings 5
MANAGING THE Turn to mix the compost periodically, ideally after the temperature in the middle of the pileCOMPOSTING has reached 140°F, to encourage uniform aera- tion of the pile. Add water if the pile dries out.PROCESS Compost can be ready to use in as soon as a month or as long as a year, depending on the Any number of systems may be used to kinds of materials added and how the compostcontain and manage compost. But any com- pile is managed. Finished compost should lookpost system that you choose should be deter- like a uniform potting soil with little distinguish-mined by how well you will be able to man- able evidence remaining of what materials wereage the compost process. Whether using a originally added to the pile.cage, a pile, or a turning unit, the followingsequence should be followed to properlybuild and manage the compost. Construct a compost pile in layers, alter-nating yard wastes, a nitrogen source, ifneeded, and soil or ﬁnished compost (to pro- USINGvide an inoculation of beneﬁcial microorgan-isms). Begin with a 6-inch layer of coarse ma-terials such as small twigs or branches. Then FINISHEDplace ﬁner materials such as leaves or grassclippings in a layer about 6 to 8 inches deep. COMPOST ompost can be used to improveIf wood chips or other higher-carbon materi-als are placed in this layer instead of leavesor grass clippings, add about 1 cup of 10-10- C soil aeration and structure, add nutrients to garden soil, and hold10, 10-6-4, 13-13-13, or similar analysis fertil- water and nutrients in sandy soils.izer, or manure. The ﬁnal layer consists of Compost can also be used as a mulchsoil or ﬁnished compost 1 to 2 inches deep. to conserve soil moisture, suppress This sequence of layers is repeated with weeds, prevent crusting of the soilthe exception that the coarser material is surface, and buffer soil temperatures.omitted with subsequent layers. Just about Composting is an inexpensive andany plant waste can be added to the compost ecologically sound way to recyclepile. Kitchen scraps such as vegetable and yard and garden wastes, improve yourfruit scraps, egg shells, and coffee grounds soil, cut down on waste disposalcan be added to the pile, but make sure they costs, and save considerable space inare buried in the pile to avoid odor. Do not our bulging landﬁlls.add meat scraps, bones, or fats to the com-post pile because they will attract unwantedanimal and insect pests. This publication was prepared by Dave Williams, Extension Horticulturist, Associate Professor; Jim Donald, Extension Agricultural Engineer, Professor; Bill Goff, Extension Horticulturist, Professor; and Tony Glover, Extension Area Agent; all in Horticulture at Auburn University. For more information, call your county Extension ofﬁce. Look in your telephone directory under your county’s name to ﬁnd the number. Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, ANR-638 sex, age, veteran status, or disability. UPS, 15M31, Revised Oct 1997, ANR-638