If you are planning to start a vegetable garden or if you have one already, you may be wondering what’s in your soil and is it healthy enough to grow food in it? The University of Minnesota (UMN) Soil Testing Laboratory offers tests for lead as well as organic matter, pH, phosphorus, potassium, and more.
Testing your soil requires taking a soil sample. This entails digging soil from several areas to a depth of six inches for garden areas and mixing them to produce a pint of soil. Further information is available at their website (soiltest.cfans.umn.edu); a lead test costs $15, and a regular test, which includes pH, organic matter, and more, costs $15 and requires a separate sample. Lead content in soil is reported in parts per million (ppm); it is recommended that foods not be grown in soil that measure above 300 ppm, or 100 ppm if children may be exposed to the soil.
The highest lead exposure results from direct intake of soilâ€”therefore, children and adults should wash hands after playing or working outside, and all fruits and vegetables should be washed before eating. Leafy vegetables such as spinach and root vegetables such as potatoes absorb more lead from the soil than fruiting plants such as tomatoes.
Arsenic may also diffuse into soils from some pesticides, chromated copper arsenic pressure-treated wood, and other means. The Minnesota Department of Health provides suggestions for avoiding arsenic exposure from CCA-treated wood. Minneapolis residents in the vicinity of Hiawatha and 28th may be concerned about arsenic from a former pesticide plant. The EPA maintains a complete web site about this area, which includes instructions for soil testing: epa.gov/Region5/sites/cmcheartland.
The UMN extension offers some tips for reducing lead intake from foods grown in contaminated soil: wash all produce thoroughly in a vinegar or soap solution; remove outer leaves of vegetables; and peel root vegetables. To reduce lead uptake by plants, use lime to maintain a soil pH above 6.5, which makes the lead in the soil less available to the plants; high soil phosphorus has a similar effect. Organic soil amendments such as compost, in combination with a pH above 6.5, also make lead less available. In older areas where lead paint or gasoline may have left residues, gardens should be located away from houses and streets.