Risks of using manure as a garden fertilizer

May 23, 2005 (Updated December, 2007)
Carol Ann Burtness
University of Minnesota Extension Regional Extension Educator, Food Science
E-Mail: burtn002@umn.edu

Vegetable gardeners add fertilizers to gardens to improve the soil and add nutrients for an extra growing boost. There are potential food safety risks if you plan to use manure as a fertilizer on your vegetable garden.

Some bacteria that are associated with foodborne illnesses can be found in fresh manure because these bacteria are a natural part of animal intestinal tracts. Vegetables can be contaminated if they are grown in soil where manure has been applied or where soil splashes onto vegetables due to rain or irrigation.

The USDA National Organic Program is concerned about vegetable-growers using manure as a fertilizer and recommends that manure be applied at least 120 days before harvesting vegetables. For most gardeners in Minnesota, this recommendation does not work because the time between fertilizing and harvesting is shorter than 120 days!

To reduce risks of contaminating vegetables when using manure, consider these options:

• Move your vegetable garden to a location that is not affected by surface runoff from manure storage or from crop land spread with manure.
• Avoid contaminating your vegetable garden from wind-borne drift during manure-spreading.
• Use sterilized manure that is available from gardening stores.
• If you plan to apply manure to your garden this year, use properly composted manure.
• Apply non-composted or fresh manure only in the fall of the preceding harvest year. Minnesota's winter weather will destroy pathogens that may be present in fresh manure.
• If you apply non-composted or fresh manure in the spring, make sure there are 4-6 months of time between fertilizing and harvesting or on soil used in growing late-season vegetables.

All produce grown in a manure-fertilized garden should be thoroughly washed in clean cold water and peeled (if possible) to reduce the risk of contamination. Cooking vegetables also reduces or eliminates the contamination risk. Other tips for washing fresh produce include:

Other tips for washing fresh produce include:

• Wash produce just before serving not before storing because washing will cause produce to spoil faster.
• Scrub produce with a firm skin or hard rind like carrots, potatoes, melons or squash with a vegetable brush and cool running water.
• Always wash squash and melons, even if you never eat the rind or skin because when cut, dirt or bacteria that are on the outer surface can be transferred to the inner flesh.
• Throw away outer leaves of leafy vegetables such as lettuce and cabbage before washing.
• Do not wash fresh produce with detergent or bleach solutions. Fruits and vegetables are porous and can absorb the detergent or bleach, which is not intended for use on food and consuming them, has the potential to make you sick.

To enjoy your home-grown produce and reduce contamination risks from using manure as a fertilizer, use a common sense approach and wash the produce before eating.