Soil from gardens that were recently flooded may not be safe for growing fruit and vegetables this summer.
Depending on the location, flood waters may contain contaminants such as agricultural or other chemicals, as well as disease-causing organisms from fresh manure, animal carcasses, septic systems, and even lagoons.
Commonly found pathogens include E. coli 157, listeria, clostridium, campylobacter, giardia, and others. All these diseases make people very ill and, in some instances, have long-term complications or may be fatal.
For that reason, FDA rules prohibit the sale of any produce from flooded gardens. (Pooling within a field without entry of water from outside the field is not considered flooding.)
If there is a high likelihood of chemical contamination, the area should not be used for gardens this year. If the contaminants are known, the soil can be tested for those chemicals prior to next year’s planting.
However, these tests can be quite expensive, especially if more than one type of chemical needs to be tested. Fruit from trees that survive early spring flooding should be safe as long as the new growth of the tree looks normal, as roots and even fruit stems exclude most contaminants from being transported into the fruit.
If the likelihood of chemical contamination is low, biological contamination must be considered.
Any produce that contacts flood waters or is grown in ground that was flooded this spring should be thoroughly cooked to destroy pathogens. This includes low-growing fruit such as strawberries.
During heavy rains pathogens can be splashed onto produce from contaminated soil. Replace any organic mulch, such as straw or grass clippings, that was contacted by flood waters.
Studies have shown that human disease pathogens can survive in the soil for six months or longer after a contaminating flood.
Surface washing is not sufficient to remove pathogens, as they can attach themselves to produce and form a film over themselves that is very difficult to remove by washing or scrubbing the produce.
They can also enter any cracks in the produce. Cantaloupes are particularly at risk, since netting on their surface harbors bacteria.
Gardeners sometimes ask whether it is safe to grow produce that will not touch the ground, such as staked or caged tomatoes, peppers and similar plants.
To prevent possible contamination, the plants should be trellised, staked or caged to prevent tissue from touching the ground, and freshly mulched to prevent soil splash.
If in doubt, grow produce that will be thoroughly cooked before use, such as squashes, pumpkins, potatoes, or beets. Any of the root crops should be peeled and cooked thoroughly for the rest of the season (six months).
An option to consider for future seasons may be the use of raised beds, filled with a mixture of compost and fresh soil from an unflooded area.
Always wash fresh fruits and vegetables with running water before eating, and use friction. Some sprays approved for use on fruits and vegetables are available and may be helpful in removing debris, dirt and some surface microorganisms, but not those microorganisms that have infected the produce long enough to form that protective film.
Do not use detergents, which are not tested or labeled for use with fresh produce. Use of chlorine bleach is not recommended. It must be carefully monitored by trained persons to obtain proper dosage and effectiveness and even then will not remove bacterial films from produce.
Always use good personal hygiene practices when working with fresh produce. Wash your hands before and after gardening.
Young children can be at a high risk for some foodborne illnesses. If a garden plot has been flooded, consider not allowing young children in the garden with you.
Information excerpted from Rhoda Burrows, SDSU Extension horticulture specialist