COMPOSTING Barbara J. Bromley, Mercer County Horticulturist 04

"..Equal weights of green and brown, help the microbes break it down.."

For decades we were putting our household, industrial, and municipal wastes into landfills. Common sense told us that this had to stop, especially in the highly populated Northeast. Most municipalities have programs that recycle glass, newspaper, office paper, cans, some plastics and woody brush, but this isn’t enough.

Up to 75% of household garbage is organic, or carbon-based, material. It winds up in those landfills or is destined for incineration. Environmental consciousness dictates that these materials be recycled by composting.

Composting is nothing new. Nature has been composting in field and forest for millennia. Leaves, needles, bark, insects, dead animals, and branches have dropped to the ground and slowly decomposed. This resulting decomposed organic matter, or humus, enriches the soil and releases nutrients that feed forest plant life.

COMPOSTING: the process by which organic matter (any material that was once living) is converted into humus. Compost, the material produced, consists largely of decomposed organic matter and can be used to condition and provide nutrients to soil.

COMPOSTING OBJECTIVES

•To make productive use of organic materials that would otherwise go to landfills or incinerators.

•To correct the disruption of the natural cycle of decay that occurs in gardening, land development, and farming by mimicking the process of death and rebuilding that occurs in nature

•To reduce the mass, volume, and carbon to nitrogen ratio (C:N) of organic wastes.

•To produce a usable product.

COMPOSTING PROCESS

Producing compost is easy. Organic materials (see list of compostable materials) are piled together and allowed to decompose over time. This decomposition is accomplished by the digestion of plant and animal material by soil microorganisms. The heat in a compost pile is the result of oxidation or "biological burning." The compost is ready to use when everything in the pile is brown and crumbly and individual components are no longer identifiable. The original organic materials have decomposed into a relatively stable material called humus.

If organic materials such as leaves are just dumped in a pile and left to decay, decomposition generally takes place slowly over a couple of years. Home gardeners who practice composting are usually looking for a usable product more quickly. The rate at which organic matter will break down can be accelerated by:

•chopping or shredding materials into small pieces

•mixing equal weights of green (high nitrogen) and brown (high carbon) materials

•turning the pile regularly

•keeping the pile moist, but not wet

It is not necessary to create layers of different materials in the pile or bin. Very high nitrogen, or green materials such as fresh grass clippings, should be blended with high carbon, or brown, materials to prevent overheating and anaerobic smells.

FACTORS AFFECTING DECOMPOSITION

TEMPERATURE: The best internal working temperature is between 70 and 140°F. Decomposition will still occur whenever the pile is above freezing, but will occur more slowly the lower the temperature. Appropriate temperatures encourage the activity of thermophyllic, or heat-loving, microorganisms.

OXYGEN: Aerobic decomposition occurs when oxygen levels are at or above 5%. When there is no oxygen, anaerobic decomposition (which produces bad smells and "pickling") starts. Turning the pile increases the oxygen level.

MOISTURE: Water is added to a pile until it is as moist as a wrung-out sponge. For rapid composting a moisture content of 50-60% is best. A cover or tarpaulin over the pile will prevent it from getting too wet during heavy rain or drying too fast during drought or hot weather. Decomposition stops when a pile is too dry and becomes anaerobic if too wet.

NUTRIENTS: Nitrogen is necessary for decomposition to occur. If there is not enough "green" or high nitrogen material in the pile, adding a nitrogen fertilizer or manure will help.

pH: The acidity of the finished compost is nearly neutral (pH of 7), so adding lime is not necessary. Rotted oak leaves and pine needles are only slightly more acidic.

TIME: The time needed for decomposition to occur ranges from 2 weeks to 2+ years and is dependent on other necessary factors. (Organic materials buried deep in a landfill may never decompose because of the absence of oxygen).

MICROBES: "Compost accelerators" are usually not needed. There are enough microorganisms on leaf surfaces, in the soil on roots of weeds, etc. for decomposition to occur.

CARBON TO NITROGEN RATIO: The ideal C:N ratio for rapid decomposition is about 25 or 30:1. A reasonable range is 20:1 to 40:1. By comparison, wood chips are about 400:1, fresh grass clippings about 12:1.

PARTICLE SIZE: Small pieces break down more rapidly and give a more even result.

 

COMPOSTING STRUCTURES

Fancy or expensive bins are not necessary for successful composting. Small amounts of organic matter can be spread over a garden or other soil area and turned into the soil in a process called "sheet composting." Small quantities of kitchen or yard waste can also be buried 12 inches deep at intervals throughout the garden. With care, apartment and condominium dwellers with no yard space can compost in plastic garbage bags, trash cans or with worm boxes It is also possible to just build a pile of materials without any framing at all, the traditional compost "pile."

For neatness and efficiency, a bin or container may be desired. Good working sizes for bins range from 3ft x 3ft x 3ft to 5ft.x 5ft x5ft. When a bin is filled, the contents will heat up to 140°F or higher accelerating the decomposition process and possibly destroying disease organisms and weed seeds. A smaller pile, or just a few materials added to a bin at a time, called "cold composting," will not heat up as efficiently. A pile taller than 5 feet may weigh itself down and drive out oxygen.

Composting units can be above or below ground, permanent or temporary, framed or unframed, rectangular or cylindrical, beautiful or "functional." They can be individual bins, called holding bins, where materials are added and held until they decompose, a relatively slow process. They can be multiple bins, called turning bins, where materials that have partially decomposed are shoveled or turned into an adjacent bin. Fresh material is now placed in the vacated bin. Because turning tends to accelerate decomposition, this is a faster method. Some possibilities for bins and methods include:

Holding Bins:		Turning Bins:
•Portable wood and wire (cage-type) bin		•Wood and wire 2 or 3-bin unit
•Concrete block or brick bin		•Concrete block 2 or 3-bin unit
•Board-construction bin (New Zealand box)		•Wooden 2 or 3-bin turning unit
•Stationary barrel or drum composter		•Rotating barrel composter
•Pallet bin		•Various manufactured bins
•Log or rail bin
•Picket or snow fence enclosure
•Wire fence bin
•Concrete or masonry lined pit
•various manufactured bins

Also:

•Worm box (vermicomposting - indoors or out)
•Open pile
•Something you create

Considerations when deciding which container/method to use are:
•personal taste
•labor involved
•expense of materials
•availability of materials
•space available

 

MATERIALS TO COMPOST

Any of the following organic materials will eventually decompose in the presence of oxygen and moisture, but the smaller the particle size, the faster the decomposition. For example, chopped up flower stems decompose more quickly than whole stems.

Vegetable waste, grass clippings, manures, and coffee grounds are relatively high nitrogen. Dried leaves, corn cobs, paper, wood chips, sawdust, and straw are relatively high carbon.

banana skins	leather	wood ash	watermelon rind
feathers	dried blood	tea bags	yard waste
grass clippings	newsprint (b&w)	crop waste	potato peels
manures	eggshells	cornmeal	leaves
oatmeal	sawdust (not treated)	paper/cardboard	wood chips
old seed packets	flour	flowers	shredded hardwood
seaweed	fish scraps (buried)	seashells (crushed)	corncobs
straw and hay	powdered milk	bone meal	ground bones
tobacco	pine needles	peanut shells	bird cage "stuff"
vacuum bag wastes	stale cereal	cottonseed meal	old potting soil/mix
wood shavings	dead insects	kitchen scraps	hair (human, animal)
rock powder (green-sand, granite dust)	coffee grounds (with paper filter)	weeds (most, but not all)	natural fibers (cotton, linen, wool)

DO NOT COMPOST:

The following may release unpleasant smells as they rot, spread weeds or diseases, contaminate the compost, or attract rodents or other animals.

meat	grease, fat, oil	most dairy products	human waste
unground bones	used kitty litter	weed seedheads	poultry
non-organics	colored newsprint	large woody brush	dog or cat feces
diseased plants (esp. tomato)	treated wood (or sawdust)	roots or stems of hard-to-kill or noxious weeds	fish waste (unless buried deeply)

TROUBLESHOOTING

•Pile temperature too hot (over 150°F.): turn the pile.

•Pile too cold: add larger amounts of green and brown materials so their weights are approximately equal, check moisture level, wait for spring.

•Pile gives off an ammonia smell: add more high carbon material and turn the pile.

•Decomposition stopped: add a high nitrogen material, turn the pile, check moisture level, cut materials in smaller pieces.

•Pile too wet: mix in an absorbent organic, such as shredded newspaper, and turn the pile. Cover.

•Infested with flies or other insects: turn the pile, maintain adequate but not excessive moisture, turn in kitchen scraps immediately after adding.

•Infested with rodents: turn in kitchen scraps immediately after adding or stop adding for a while, use a rodent-proof bin, place hardware cloth or other medium (1/4-1 inch) mesh screening under the bin to prevent tunneling.

REASONS FOR USING COMPOST

Applying a one half to three inch layer of compost (humus) to the garden each year in spring or fall will:

1. Save money over the cost of peat moss and other organic soil amendments.
2. Increase tilth (soil structure, aeration and fertility).
3. Add varying amounts of essential nutrients (major and trace) to the soil.
4. Act as a buffer and increase the cation exchange capacity (CEC).
5. Tie up iron and aluminum.
6. Provide an energy source for microorganisms and earthworms and stimulate biological activity in the soil.
7. Act as a useful mulch to keep down weeds, help moderate soil temperature, help decrease evaporation, reduce soil erosion, and look attractive.
8. Make the soil darker, enabling it to absorb more heat from the sun. This extends the gardening season in both spring and fall.
9. Increase the water-holding capacity of the soil and act as a drought protection. (100 lbs. of humus holds 195 lb. of water.)

 

See information and photos of the compost bins at the Mercer County Home Compost Demonstration Site and Gardens.

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