Manure Safety

Tips on keeping the soil, plants and you healthy.

Manure from many farm animals can be a valuable addition to your soil. Not only does it add such enriching nutrients as nitrogen, phosphorus and potassium, but manure also helps retain moisture and loosen compacted ground.

Gardeners and farmers should use manure with caution, however. When it’s fresh, it often contains weed seeds and has a strong odor. Composting, aging and stockpiling can help kill viable seeds and pathogens, and control the smell. See below for brief definitions for each and links for more information.

The most important thing to remember is that manure has the potential to cause serious illnesses and death in humans. Improperly handled animal waste can transmit disease-causing pathogens and parasites such as Listeria, E. coli, roundworms, tapeworms and other organisms.

The greatest risk is with root crops, like carrots, and leafy vegetables, such as lettuce, because the edible part of these plants physically touches soil that has manure in it. The good news is that you can use animal manure safely, if you follow recommended precautions such as the following.

In the Garden

Never apply fresh manure after planting.

Wait at least 120 days from the time you apply fresh manure to the time you harvest high-risk crops, unless you’re going to thoroughly cook them before eating them. Again, high-risk crops are those that have edible parts that come in direct contact with the soil.

While some sources suggest also waiting 120 days from the time you apply fresh manure to the time you harvest crops that are not considered root or leafy crops, others recommend just 90 days.

Use only composted manure if you’re applying it within 60 days of harvest. “Composted manure” means it’s been in a pile long enough for living organisms in the manure to generate sufficient heat to kill off most pathogens and weed seeds—that’s typically from 1 to 3 months. The time required depends on what animal the manure is from; how long it’s been stored; whether there’s animal bedding mixed in; and whether the manure has been turned, watered and/or covered.

“Aged” manure means it has been stored and exposed to the elements for at least one year. “Stockpiled” manure is often used interchangeably with “aged,” but in some circles it’s defined by its storage of eight months or less, because the soil or field conditions aren’t suitable for spreading it (often because the ground is frozen or covered with snow). In other circles, stockpiled refers to manure that’s been piled for years, if not decades. Still, to be safe, if manure is not to be composted, it’s best to not apply within 90 days of harvest.

Consider the source before you use fresh manure. Use only fresh manure from healthy, disease-free animals or flocks. Also, if you’re getting manure from someone else, ask if they regularly use antibiotics in their feeding routine. Animals fed antibiotics excrete them in their manure, and some researchers believe that produce grown in soil treated with such manure may absorb some of those antibiotics. Humans who then eat the produce may ingest traces of the antibiotics and thereby lessen the ability of those antibiotics used to combat harmful bacteria. The debate over possible health issues is continuing.

Never put cat, dog or pig manure, in your garden or compost pile. That said, it’s best to not allow these animals in the garden. Their manure can transmit diseases that pose serious threats to human health.

Because the term “compost” is not regulated, many products can be offered by that name.  If you buy commercially packaged, composted manure at a garden center or nursery, check the label to see if it is pathogen-free. For safety’s sake, use only manure that’s labeled pathogen-free.

In the Kitchen

Wash your hands thoroughly after you’ve been in the garden or after handling animals. The proper way to wash is to scrub your fingernails, hands and between your fingers with hot, soapy water for at least 20 seconds. Dry your hands with a clean towel or a single-use towel.

While thoroughly cooking produce is the best way to prevent infection by foodborne illnesses, eating raw fruits and vegetables can be made safer by thoroughly washing and/or peeling them. Wash with clean, potable water.

People who are susceptible to foodborne illnesses should avoid eating uncooked vegetables or fruits from gardens where manure has been used.

Pregnant women, very young children, and people with chronic diseases such as cancer, kidney or liver disease, diabetes, or AIDS, should also avoid eating uncooked foods from manured gardens.

Resources

Manure Management

• USDA http://wqic.nal.usda.gov/agricultural-environmental-management/manure-management

• Many university-affiliated extension services also publish information on using animal manure in gardens and on farms. See this article from Colorado State University, or search the web for safety guidelines in your state: http://www.ext.colostate.edu/mg/gardennotes/242.html

Composting

Environmental Protection Agency http://www.epa.gov/osw/conserve/rrr/composting/index.htm

USDA http://afsic.nal.usda.gov/soil-and-water-management/compost-and-composting

Aged Manure

Plant care and growing advice for the small-acreage gardener. http://yardener.com/YardenersPlantHelper/YardCareTechniques/Composting/BuildingCompostBin/CementBlockBins/CaringForTheSoilInTheLandscape/SolutionsForSoilProblems/IncreasingOrganicMaterialInYourSoil/AgedManure

Organic Products

Organic Materials Review Institute http://www.omri.org/

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