Manure is the oldest fertilizer known to civilization. Many gardeners feel manure is superior to synthetic products. The use of manure however, does present a small risk of food-borne illness from manure contamination. Possible contaminants include salmonella, listeria, E. coli 0157:H7, roundworms, and tapeworms. Fortunately the risk of illness can be minimized in several ways.
Root crops, such as radishes and carrots, as well as leafy vegetables like lettuce where the edible part touches the soil present the greatest risk for potential problems. Washing and/or peeling will remove most potential pathogens. Thorough cooking is even more effective because most pathogens cannot survive high temperatures.
To further reduce the risk of diseases, manure should be applied at least 60 days before harvesting any vegetables that will be eaten without cooking. The best procedure is to apply manure in the fall so time and cold temperatures can destroy potential pathogens. Do not apply manure after the garden is planted. Use well-composted manure rather than fresh. Fresh manure has the potential to burn plants. For perennial crops such as asparagus and rhubarb, fertilize after the harvest season is completed. Avoid the use of cat, dog, or pig manures in gardens or compost piles. Some of the parasites found in these manures may survive and remain infectious for people.
Some people are especially susceptible to food-borne illnesses. These people should use good food handling practices or avoid eating uncooked vegetables from manured gardens. People at risk include pregnant women, very young children, and individuals with chronic diseases such as cancer, kidney failure, liver disease, diabetes, or AIDS.
Manure has and will continue to be an excellent garden fertilizer. As with many things we use, certain precautions should be taken to prevent potential problems.
This article originally appeared in the June 17, 1994 issue, p. 93.