The Back Garden Project: On Soil

Posted by Gordon Douglas


This is the seventh post in The Back Garden Project, one GOOD community member's effort to turn a neglected corner of the city into a thriving garden.

Exciting news to report: As I mentioned in my first post, I had sent a sample of my back garden soil up to Williamstown, Massachusetts, to be tested by my partner's uncle, Dr. Henry Art, a professor of biology and environmental studies at Williams College, and his colleagues. The results are in and they're amazingly bad.

Both New York State and the United States EPA set the upper limit for safe lead contamination at 400 parts per million, and at least some scientists suggest (pdf) that even that number could be dangerous in a gardening context.

My soil? To quote a lab technician who helped test it, "it calculated out as 1,811 ppm Pb+2 (that's one thousand eight hundred NOT one point eight) in dry soil." Or, as Hank put it: "The soil sample turns out to be nearly ore-grade in terms of lead."

Awesome. Now of course this is just one little sample from one random corner of the garden (in fact, as I clear and replant more areas I am finding significantly less trash-filled patches), but I'm not taking any chances with any of it. The doctor prescribes raised beds over landscape fabric to reduce the lead's "upward movement." Thanks, Hank!

Fortunately the planter I built last week has a half-assed wood-chip barrier, and anything I might eat will be growing in separate containers. (If you're curious, it's also worth remembering that some plants—particularly lettuces and other green veggies like broccoli—are more susceptible to bad soil. In the case of tomatoes, for example, lead affects the plant's health, but does not appear to compromise (pdf) the safety of the fruit, even at levels higher than those in my soil.)

In other dirt-testing news, I also checked the pH level of my soil using the handy and affordable "rapitest" soil tester. This time I took my sample from the area where I'm planting my native shade garden, where I haven't already mixed packaged garden soil in, and results are a little more promising.
That looks like very neutral soil to me, which is good for most plants and certainly fine for my ferns, mayapple, and other native ground cover. I'll want to drop the pH some for the berries I'm planning on planting, though.

The soil kit has the option of testing for nitrogen, phosphorous, and potash too. It's a slightly messier-sounding process, but I hope to get around to that soon. Next time: a visit to the Brooklyn Botanic Garden's very own Native Plant Garden, and lots of pictures of plants.