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The Rapid Composting MethodThe author is Robert D. Raabe, Professor of Plant Pathology, Berkeley.

Composting is a process in which organicsubstances are reduced from large volumes ofrapidly decomposable materials to small volumesof materials which continue to decompose slowly.in this process, the ratio of carbon to otherelements is brought into balance, thus avoidingtemporary immobilization of nutrients. One of themany benefits of adding compost to the soil is thatthe nutrients in it are slowly released to the soiland are then available for use by plants.Decomposition will take place in soil ifundecomposed organic materials are added to it,but in the breakdown process nutrients will be tiedup and unavailable for plants to use. This mayresult in nutrient deficiencies and poor growth,especially if large amounts of material are added.

The old method of composting was to pile organicmaterials and let them stand for a year, at whichtime the materials would be ready for use. Themain advantage of this method is that little workingtime or effort is required from the composter.Disadvantages are that space is utilized for a

whole year, some nutrients might be leached dueto exposure to rainfall, and disease producingorganisms, some weeds, weed seeds and insectsare not controlled.

Recently, a new method has been developedwhich corrects some of the problems associatedwith the old type of composting. With this process,compost can be made in 2 to 3 weeks.

Extra effort on the part of the composter isrequired in exchange for this time saving, but for

those who want large amounts of compost, or forthose who wish to convert materials which areusually wasted into useable compost, the effort isworthwhile.

There are several important factors essential to therapid composting method. Because all areimportant, there is no significance to the order inwhich they are listed here.

1. Material will compost best if it is between 1/2 to1-1/2 inches in size. Soft, succulent tissuesneed not be chopped in very small piecesbecause they decompose rapidly. The harder orthe more woody the tissues, the smaller theyneed to be divided to decompose rapidlyWoody material should be put through agrinder, but most grinders chop herbaceousmaterials too finely for good compostingChopping material with a sharp shovel iseffective. When pruning plants, cut material intosmall pieces with the pruning shears-it takes alittle effort but the results (and the exercise!) aregood.

2. For the composting process to work moseffectively, material to be composted shouldhave a carbon to nitrogen ratio of 30 to 1. Thiscannot be measured easily, but experience hasshown that mixing equal volumes of greenplant material with equal volumes of naturallydryplant material will give approximately a 30/1carbon to nitrogen (C/N) ratio. Green materia

can be grass clippings, old flowers, greenprunings, weeds, fresh garbage and fruit andvegetable wastes. Dried material can be deadfallen leaves, dried grass, straw and somewhawoody materials from prunings. Such materialsare easy to find in fall and early spring but aremore difficult to find in the growing seasonDuring this time, paper bags, cardboard boxescereal and milk cartons, and paper can beused for dried materials but they must be finelychopped or shredded. Newspapers can beused if shredded and separated by plant

tissues so they do not mat - matting is badbecause oxygen is necessary for rapiddecomposition and matting excludes oxygen

Any material which is cut green and is allowedto dry is considered green. Some greenmaterials, such as grass clippings also maymat if care is not taken to separate them usingdry materials.

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3. Composting works best if the moisturecontent of materials in the pile is about 50 percent.This is not easy to measure, but with experiencethe correct amount of moisture can be estimated.Too much moisture will make a soggy mass, anddecomposition will be slow and will smell. if theorganic material is too dry, decomposition will be

very slow or will not occur at all

4. Heat, which is very important in rapidcomposting, is supplied by the respiration of themicroorganisms as they break down the organicmaterials. To prevent heat loss and to build upthe amount of heat necessary, a minimumvolume of material is essential: a pile at least36" x 36" x 36" is recommended. If less than32", the rapid process will not occur. Heatretention is better in bins than in open piles, sorapid composting is more effective if bins areused. In addition, the use of bins is muchneater. High temperatures favor themicroorganisms which are the most rapiddecomposers; these microorganisms function atabout 160

oF (71

oC) and a good pile will

maintain itself at about that temperature. Athermometer to measure temperatures insidethe pile is helpful although not necessary.

5. The compost pile needs to be turned to preventthe pile from getting too hot. if it gets much

above 160

o

F, the microorganisms will be killed,the pile will cool, and the whole process willhave to start from the beginning. By turning thepile it will not overheat, and it will be aeratedalso, both of which are necessary to keep themost active decomposers functioning.

The pile should be turned so that material whichis on the outside is moved to the center. In thisway, all the material will reach optimumtemperatures at various times. Due to heat lossaround the margins, only the central portion of

the pile is at the optimum temperature. Becauseof the necessity for turning, it is desirable tohave two bins so the material can be turnedfrom one into another. Bins made withremovable slats in the front make the turningprocess easier.

Bins with covers retain the heat better than dothose having no covers. Once thedecomposition process starts, the pile becomes

smaller and because the bin is no longer full,some heat will be lost at the top. This can beprevented by using a piece of polyethyleneplastic slightly larger than the top area of thebins. After the compost is turned, the plastic isplaced directly on the top of the compost and istucked in around the edges.

If the material in the pile is turned every day, itwill take 2 weeks or a Iittle longer to compost. Ifturned every other day, it will take about 3weeks. The longer the interval between turningthe longer it will take for the composting tofinish.

6. Once a pile is started, do not add anything (withperhaps one exception, which will bementioned in 9). The reason is that it takes acertain length of time for the material to breakdown and anything added has to start at thebeginning, thus lengthening the decompositiontime for the whole pile.

Excess material should be as dry as possibleduring storage until a new pile is started. Moisstored materials will start to decompose and ifthis occurs, they will not do a good job in thecompost pile.

7. Nothing needs to be added to the organic

materials to make them decompose. Themicroorganisms active in the decompositionprocess are ubiquitous where plant materialsare found and will develop rapidly in anycompost piles.

8. If done correctly, a pile will heat to hightemperatures within 24 to 48 hours. If it doesn'tthe pile is too wet or too dry or there is notenough green material (or nitrogen) present. Itoo wet, the material should be spread out todry. If too dry, add moisture. If neither of these

then the nitrogen is low (a high C/N ratio) andthis can be corrected by adding materials highin nitrogen (such as ammonium sulfate, grassclippings, fresh chicken manure or urine dilutedI to 5).

9. If the C/N ratio is less than 30/1, the organicmatter will decompose very rapidly but there wilbe a loss of nitrogen. This will be given off as

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ammonia and if this odor is present in or arounda composting pile, it means that valuablenitrogen is being lost in the air. This can becounteracted by the addition of some sawdustto that part of the pile where there is anammonia odor - sawdust is very high in carbonand low in nitrogen (a high C/N ratio) and

therefore will counteract the excess nitrogen.Other than adding water should the pilebecome dry, this is the only thing which shouldbe added to a pile once it's started. Becausecomposting can be done anytime, during therainy season some covering of the pile may benecessary to keep the composting materialsfrom becoming too wet.

10. Materials which should not be added to acomposting pile include soil, ashes from astove or fireplace, and manure fromcarnivorous (meat-eating) animals. Soil addsnothing but weight to a compost pile and willdiscourage the turning of the pile which isnecessary for the rapid composting process.Wood ashes will not decompose. Most soils inCalifornia have a basic pH and as wood ashesare basic, they should not be added to acompost pile or to the soil. Manure fromcarnivorous animals such as dogs, cats, lions,tigers, etc., could contain disease-producingorganisms that might infect humans. It is not

known whether or not the rapid compostingprocess will kill these organisms and thereforesuch manures should not be used - manuresfrom herbivorous animals such as rabbits,goats, cattle, horses, elephants or fowl can beused.

11. The rapid decomposition can be detected by apleasant odor, by the heat produced (this iseven visible in the form of water vapor givenoff during the turning of the pile), by thegrowth of white fungi on the decomposing

organic material, by a reduction of volume,

and by the change in color of the materials todark brown.

As composting nears completion thetemperature drops and, finally, little or no heais produced. The compost is then ready touse. If in the preparation of the compost, the

material was not chopped in small piecesscreening the material through 1-inch-meshchicken wire will hold back such pieces. Thesecan be added to the next pile and eventuallythey will decompose.

Advantages of the rapid composting systeminclude:

The production of a valuable soil amendmenfrom many organic materials which normallymight be wasted.

Compost can be made ready for use in asshort a time as 14 to 21 days.

Rapid composting kills all plant diseaseproducing organisms if done as described. Itdoes not inactivate heat resistant viruses suchas tobacco mosaic virus.

Insects do not survive the composting processThough some may be attracted to the pile, if

they lay their eggs in the compost the wildestroy them.

Most weeds and weed seeds are killed. Someweeds such as oxalis bulbs, seeds of burrclover, some amaranthus seeds and seeds ofcheese weed are not killed by the hightemperatures in the pile.

In addition to the above, outdoor exercise is anadded benefit.

This composting project was supported in part by a grant from the Elvina J. Slosson Fund.

Cooperative Extension University of CaliforniaDivision of Agriculture and Natural Resources

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