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GO GREEN WITH SAFE COMPOSTING
by: Nicole Swaggerty
CSU Public Health Graduate Student
People decide to compost for a variety of reasons. An avid gardener composts to produce nutrient-dense organic matter to enrich their garden soil. Others want to reduce the amount of food and yard waste that goes to the landfill. Whatever the reason, it is important to understand how to properly and safely compost to prevent contamination of fruits and vegetables from the garden. It is particularly important with garden produce that grows in direct contact with the soil and is eaten raw, such as carrots, radishes, leafy greens, strawberries, and melons. Selecting the right materials to compost and handling them correctly can safer for you and beneficial for your garden.
Farmers have used animal manure and bedding as soil amendments for centuries. High in nitrogen, manure is perfect for getting a compost pile cooking. Cow, goat, sheep, chicken, rabbit, and horse manure can be used in a compost pile. However, manure from pigs, cats, and dogs should be avoided. Meat eating animals are more likely to harbor bacteria in their intestinal tract that are pathogenic to humans, and pig manure may harbor parasites. The pathogens Salmonella, Listeria and E. coli O157:H7, as well as parasites such as roundworms and tapeworms have been linked to applications of manure to gardens. These bacteria may not be destroyed by the heat in the compost pile and may survive up to a year or longer. Therefore, it is advisable to ensure that animal feed does not contain any animal by-products, a good reason to know your farmer. Also, the compost bin should be inaccessible to pets, especially if using open-air piles.
Getting a compost pile ‘cooking’ is very important. The Environmental Protection Agency (EPA) states that “certain temperatures promote rapid composting and destroy pathogens and weed seeds.” Compost heat is produced as a by-product of the microbial breakdown of organic material. Regulations by the EPA specify that to achieve a significant reduction of pathogens during composting, the compost should be maintained at minimum operating conditions of 40°C (104°F) for five days, with temperatures exceeding 55°C (131°F) for at least four hours of this period. Most species of microorganisms (i.e., the good guys) cannot survive at temperatures above 60-65°C (140 - 149°F), making it important for compost managers to turn or aerate their systems to maintain the temperature in the correct range.
In composting plant materials, caution is advised when adding weeds (due to possible re-sprouting in the garden) and plants infected by an insect attack because insect eggs could survive the heat of the compost pile. Use caution when composting plants that produce compounds toxic to other plants and the soil, such as eucalyptus, bay laurel, walnut, juniper, acacia and cypress. Pine needles are also acidic and can interfere with the decomposition process; therefore, a general rule of thumb is to use no more than 10% pine needles in one’s compost pile.
Before adding plant and fiber materials, keep in mind they may have been treated with chemicals. Grass clippings from the lawn may have been treated with pesticides, which can take several months to break down; paper products, such as newspapers, contain a variety of inks (soy based inks are recommended); coffee filters and paper towels may have been treated with synthetic chemicals and bleach. Those attempting to maintain an organic garden will need to consider these possibilities before tossing items into the pile. Lastly, thoroughly clean and wash any tools, equipment, and gloves that contact manure before using in the garden area.
Approaches to composting vary. A composting connoisseur views composting as a science, whereby recipes are followed, temperatures are taken, and intricate systems are designed to optimize the decomposition process. Others take the more simplified stance that “compost happens” and not much needs to be done to make the process work. However a person approaches composting, it is still important to be cautious of risks associated with potentially harmful pathogens that can survive and thrive in the compost environment. Below is a quick reference guide to compost materials from EPA. Happy composting!
What to Compost
|The IN list||The OUT list||Why|
|Animal manure||Pet wastes and used cat litter||Might contain parasites, bacteria, and viruses harmful to humans|
|Clean paper||Diseased or insect-ridden plants||Diseases or insects might survive and be transferred back to other plants|
|Cardboard rolls||Yard trimmings treated with chemical pesticides||Might kill beneficial composting organisms|
|Coffee grounds/filters||Dairy products (milk, butter, yogurt)||Odor problems and attraction of pests|
|Eggshells||Meat or fish bones and scraps||Odor problems and attraction of pests|
|Fireplace ashes||Fats, grease, lard, or oils||Odor problems and attraction of pests|
|Fruits and vegetables||Black walnut tree leaves or twigs||May releases substances harmful to plants|
|Grass/yard clippings||Coal or charcoal ash||May releases substances harmful to plants|
|Hair and fur|
|Hay and straw|
- Good Agricultural Practices Network for Education and Training. Cornell University. Available online at: http://www.gaps.cornell.edu/indexhighspeed.html.
- Bobbitt, V. and V. Hillers, Composting Livestock Manure. WSU Cooperative Extension. Available online at: http://gardening.wsu.edu/stewardship/compost/manure/manure2.htm.
- E.P.A. United States Environmental Protection Agency. Composting. Available online at: http://www.epa.gov/epawaste/conserve/rrr/composting/index.htm.
- Islam, M., M. Doyle, S. Phatak, P. Millner, and X. Jiang. 2005. Survival of Escherichia coli O157:H7 in soil and on carrots and onions grown in fields treated with contaminated manure composts or irrigation water. Food Micro. 22:63-70.
- Wilson, C. and J. Feucht. CSU Extension Fact Sheet # 7.212, Composting Yard Waste. Available at: http://www.ext.colostate.edu/pubs/garden/07212.html.
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