Question: My friend has horses and offered that I could have the manure for my garden. Any tips? A.N.
Answer: Many vegetable gardeners, especially those interested in organic production, like to amend their soil with manure. Manure improves the soil quality, drainage, and water-holding capacity, while providing nutrients needed by growing plants. Unfortunately, fresh manure can contain bacteria that could contaminate vegetables and cause illness in humans.
The risk of contamination is so serious that the USDA National Organic Program (NOP) stipulates when non-composted or fresh manure can be applied to soil used for growing vegetables. The NOP rule states manure must be applied at least 120 days before harvest if the vegetables have edible portions that might be contacted by soil either directly or through splashing of rain or irrigation water. In Wisconsin, 120 days covers most of the vegetable growing season, so sticking to this standard is nearly impossible for same-year applications.
Research by a University of Wisconsin Extension Food Safety Specialist found that applying fresh manure less than 120 days before harvest significantly increases the likelihood that E. coli bacteria from manure will contaminate the vegetables. The interval between manure application and planting is even more important than the application-to-harvest interval because newly sprouting vegetables are very susceptible to contamination.
Manure can be safely added to your vegetable garden if you follow one of these three options.
- For same year or current season applications use only properly composted or sterilized manure, which is available from garden stores or your compost pile.
- Non-composted or fresh manure should be added to your garden only in the fall before spring planting the following year.
- If you apply non-composted manure in spring, vegetables must be planted at least 120 days after manure was added to garden. In other words, planting must be delayed until fall. Don’t allow water to run into areas planted with vegetables from locations in which fresh manure was applied.
Never use cat, dog or human waste to fertilize gardens.
Fresh produce can become contaminated by fecal bacteria from birds and other wildlife. Careful washing and peeling of vegetables reduces the risk of contamination. Cooking vegetables will lower or eliminate disease causing bacteria.
Many people like to grow their own food so they know it is safe to eat. By following the manure application guidelines you can assure your homegrown vegetables are safe.
Barb Larson is horticulture educator for Kenosha County University of Wisconsin Extension. If you have a plant or gardening question, email Larson at firstname.lastname@example.org or call her at 262-857-1942.