What's in Your Soil?

There's no real substitute for a professional soil test if you are thinking of planting a vegetable garden. But there is a terrific website that allows you to cruise around your neighborhood and get a general idea of what's in the soil and whether it will support the kind of food gardening you have in mind.

Last night I attended a two-hour class on urban soils sponsored by Casey Trees, a non-profit organization here in the District of Columbia that works to grow the city's tree canopy. The class was taught by a soil scientist from the U.S. Department of Agriculture and among the things we learned were these:

* There are thousands of different soil types around the United States, some better for gardening and planting trees than other.

* Much of the country's topsoil is disappearing because of agricultural practices that favor applications of artificial fertilizers rather than organic matter.

* Urban soils suffer from trash and compaction. Plants need oxygen in the soil to grow and a healthy soil typically is composed of 25 percent oxygen. Vibrations from heavy road traffic work to compact nearby soil.

* The "fall line" separating the upland Piedmont and Appalachian regions from the Atlantic coastal plains runs right through the middle of the District of Columbia. (It runs from New York City through Philadelphia, Washington and south all the way to Florida). Piedmont soils are distinctly different from coastal plains soils.

The USDA has spent years collecting data on soils around the country. Its latest internet tool, the "Web Soil Survey," allows you to enter an address and pull up all kinds of information on the soil in your area, including organic content, pH, and whether it rates as suitable for growing food.

When you get to the site, click on the green button to start the survey. Type in your address and you'll see a satellite photo of your neighborhood. You'll have tons of options and things to look at. You might want to set a day aside to get used to cruising around this wealth of valuable data.