One detail that first-time gardeners shouldn’t skimp on is making sure their soil is free of contaminants. Thanks to years of leaded gasoline use, lead-based paint, and coal-fired power plants that spew heavy metals into the atmosphere, many Americans have soil that’s contaminated with lead. “There’s always going to be some level of lead in the soil,” says Paul Hepperly, PhD, Fulbright scholar and senior scientist at the Rodale Institute, because it’s a naturally occurring heavy metal. “But it’s persistent in the environment because it does not decay. And [lead levels] can magnify over time.” In adults, too much lead can lead to high blood pressure and nervous system problems, but in children, lead can cause a wide range of developmental problems, from learning disabilities to brain damage. Some studies even suggest that childhood lead exposure contributes to aggressive and violent behavior later in life. Lead-based paint that flakes off into dust and soil remains the primary source of lead exposure in children.
THE DETAILS: Last May, a study published in the journal Environmental Research revealed that, of 141 backyard gardens in Massachusetts, 81 percent had lead levels above the Environmental Protection Agency’s action limit of 400 parts per million (ppm). Most of the lead came from lead-based paint, which, although banned since 1978, takes a very long time to break down in soil. The second most prevalent source of lead in soil comes from leaded gasoline particulates; leaded gas is also banned, but its leaded particulates settle in soil and linger for years.
WHAT IT MEANS: If it turns out that your soil does have high levels of lead, you don’t have to give up on gardening.
Follow these tips to cut down on soil lead levels:
• Get it tested. Soil tests are relatively inexpensive and can be performed by your local extension service. And a test does a lot more than tell you about contaminants. It will tell you the nutrient components of your soil, and what its pH is. Organic Gardening magazine recommends having a soil test done every 3 to 5 years to maintain optimum soil health. Your local cooperative extension can help; see OrganicGardening.com for tips on getting and reading a soil test.
• Go with containers and raised beds. If your soil’s suspect, don’t give up. You can grow almost any vegetable in containers. And using raised beds with healthier soil is an easy way to establish a larger garden, even in contaminated areas. If you’re going to eat what you grow, he recommends building a bed that’s 8 inches deep and sticking with plants that bear fruit, such as tomatoes, rather than root crops, such as carrots and potatoes, or leafy greens.
• Move your garden away from the house. Numerous studies have found that lead levels tend to be higher in the soil immediately surrounding the foundation of a building. Organic Gardening recommends moving your garden more than 6 feet away, just to err on the side of safety.
• Balance the pH. Maintaining a soil pH of 6 to 7 makes your soil slightly acidic to completely neutral, which immobilizes not just lead, but other heavy metals found in soil, such as aluminum.
• Add organic matter. The second best way to neutralize lead in soil is to add organic matter, such as compost or manure. Most backyard soils in this country are 1 to 2 percent organic matter, Hepperly says, while levels of 3 to 5 percent are optimal. “That will give you a greater assurance that you’ll have healthy growth and reduce the heavy metals that will be absorbed by plants.” Because commercially available compost may contain leaves, grasses, and other organic plant materials collected near roadways, it’s a good idea to get your compost tested for lead as well.