Vegetable gardeners tend to react to food scares by retreating to the garden. After all, there's nothing safer, healthier or more rewarding than growing food for your family's table. The recent recalls of spinach and leaf lettuce due to concerns over contamination with E. coli are enough to convince anybody to seed in a few extra rows of greens. But even home gardeners should take some basic precautions to keep their kitchen garden safe.
First, a look at the science: The contaminant in question, E. coli 0157:H7, is just one strain of the bacteria Escherichia coli that is especially harmful to human health. In fact, according to the Centers for Disease Control, there are hundreds of strains, many of them harmless. This particular strain is well-suited to growing in the guts of ruminants, or hoofed animals, that digest their meals in two stages. Cattle, goats, sheep, deer, llamas and buffalo are all ruminants, and all can carry and spread the bacteria directly through their manure or indirectly when that manure gets into irrigation or runoff water.
That's not the only way E. coli can be introduced to a farm or garden. "A bird or a squirrel can come into contact with manure and spread the bacteria," says Dr. Patricia Kendall, a professor at Colorado State University's Department of Food Science and Human Nutrition. "And from all of these different sources, it can show up in irrigation water, ponds or lakes. Unfortunately, it takes only a few microorganisms to cause an infection." Leafy greens are especially vulnerable to contamination because the leaves grow close to the ground and are porous, making it easy for microbes to grab hold.
But there's no need to give up on fresh greens. Dr. Luke LaBorde, associate professor of food science at Penn State, encourages gardeners to get reacquainted with the kind of common-sense precautions that should apply year-round, whether or not there's a food scare.
Here's common-sense advice from the experts:
Avoid home-composted manure. Manure must be heated to a temperature of at least 140 degrees to kill such pathogens as E. coli, and there's no guarantee that backyard compost piles will reach that temperature through the natural decomposition process, which does give off heat. "Even if they do," says Dr. LaBorde, "they might just get hot enough at the center and not around the edges." Instead, he recommends composting leaves, grass clippings and other greens.
Wear protective gear in the garden. Gloves do more than keep your hands clean. It's common practice for manufacturers to heat-sterilize bagged compost, manure and organic fertilizers carrying animal-based ingredients like bone meal and blood meal, making E. coli contamination unlikely. However, these products are subject to a patchwork of state-by-state regulations that don't necessarily guarantee a pathogen-free product. Wearing gloves when applying compost and fertilizers and wearing a dust mask when you apply powdered fertilizers are simple, inexpensive precautions that should be routine for gardeners.
But there is no hard evidence pointing to risks from using these products. "I have more questions than answers," LaBorde says. "But we should all get in the habit of using general sanitary practices." To be on the safe side, he suggests saving store-bought manure for the flower garden and using compost made from leaves and grass clippings in the vegetable patch.
Pay attention to water sources on your property. A small pond, stream or reservoir can provide much-needed irrigation and a water source for birds and other backyard wildlife, but make sure you and your children never drink from them and use them for irrigation only if the water has been determined to be safe. Contact your county extension office about having the water tested, and keep young children away. "If you have cattle or deer drinking out of those water sources," says Dr. Kendall, "the water could become contaminated. Children under 5 in particular should not swim in it."
Consider a deer fence. If you didn't already have enough reasons to want to keep deer out of the garden, here's another one: Deer can be carriers of E. coli. A deer walking through the garden can leave droppings that contain the harmful bacteria.
Educate your children about safe practices. Kids love to help with the harvest, but as LaBorde points out, "There's no telling what's on their hands." Children and those with compromised immune systems are particularly vulnerable to E. coli infection, making it all the more important that they wash their hands and use gloves in the garden.
Handle the harvest safely. "The much larger hazard is cross-contamination in the kitchen," says Dr. LaBorde. Use separate cutting boards for raw meat and fresh vegetables. To keep your harvest safe, wash your hands with soap and water when you come in from the garden, and then rinse produce thoroughly.
Remember that not all bugs are bad. After all, a handful of healthy soil is teeming with billions of bacteria, fungi and other microorganisms. Most of them are harmless to humans and help support plant life at the root zone and fight off disease. In fact, many organic fertilizers are inoculated with microbes that are particularly helpful to plants. There's no such thing as a sterile garden—nor should there be. A little knowledge and basic cleanliness are all you need to keep enjoying your harvest.
—Amy Stewart is the author of Flower Confidential: The Good, the Bad and the Beautiful in the Business of Flowers (Algonquin Books, February 2007). She lives and gardens in Eureka, Calif.