How clean is the dirt?

All dirts are not created equal. Urban dirt in particular has suffered the fallout from human activity, often with higher-than-healthy concentrations of lead, arsenic and other toxic metals that accumulate in the soil and are sucked up by plants. It’s an issue of grave importance for the millions of Americans who are food gardening. Soil testing, whether for pH, salinity, texture or heavy metals -- all of which affect how well, or if, a plant will grow -- is a good idea for anyone who intends to eat the bounty of their gardens. Several laboratories offer soil testing for home gardeners, including:

Wallace Laboratories, El Segundo. (310) 615-0116 or www.bettersoils.com. $65 per test.

EarthCo, St. Louis. (314) 994-2167 or www.drgoodearth.com. $20 to $100 per test.

-- Susan Carpenter