When you write a book you get questions. In our case, due to the sinking economy in California, they are delivered by Kevin Costner on horseback rather than by email or regular federal postal trucks. No problem, we like questions. A caveat here: like Nancy Klehm, the Green Roof Growers and Black Swan author Nassim Taleb, we prefer the term “practitioner” to describe what we do as opposed to “expert”. We favor experience over speculatifyin’ and make no claims to accuracy. But, we’re happy to take the letters from Kevin, the horse poop for compost and try our best. Here’s one question we get a lot:
Q: Y’all know where I can get my soil tested? I’ve started HUGE garden in my side yard and it just occurred to me that it is where people used to park their cars. I’m concerned about Oil or other pollutants from the cars that might still be in the soil. Any experience with this? Can I test without it costing an arm and leg?
J.R., Los Angeles
A: See my updated response here.
[Note update at bottom of this post!] There’s basically two groups of things to test for: contaminants and soil nutrient levels. There are cheap home test kits, but sending samples to a lab is much more accurate. To find a lab in the US, the best place to start is with your local Cooperative Extension Service. Find yours via this link. Some offer free or low cost soil testing.
Here in Los Angeles the Extension Service does not offer testing, but they were nice enough to provide a list of local labs. The lab I talked to, Wallace Laboratories, offered tests at $75 a sample–see their price list for specifics. Before you send a sample talk to the lab to find out what they test for and how much they charge for phone consultation in interpreting the results. If you’re worried about contaminants make sure to describe your situation.
Sampling is a DIY project. You put the soil in a bag and send it off to the lab (they’ll tell you how to dig for the sample and how much to send). You’ll probably need to do several samples since different parts of the yard might have different problems.
In the end I cheaped out and went with Peaceful Valley’s soil testing service for $29.99. No contaminant testing, but the results did tell me that I’m very low in nitrogen, with a soil ph that’s slightly alkaline. They charge for phone consultation, but I was able to interpret the results myself with their slightly overpriced booklet that you can order along with the test.
Another approach, especially if you live in an old house like ours, is to assume that your soil is contaminated, skip the test, and grow things in raised beds, containers or stick to ornamentals. You could also try bioremediation: each season plant a cover crop, let it grow, and then pull it up and dispose of it. Test the soil until it comes out clean. This works well, but it can take many years to get all the contaminants out.
For those of you in Los Angeles, our local Extension Service agent Yvonne Savio kindly sent me the following list of labs with comments.
Biological Urban Gardening Service
PO Box 76
Citrus Heights, CA 95611
Email: [email protected]
Organic recommendations, very user-friendly
Owner Steve Zien and I co-author “Organic Matters” organic gardening column in Sacramento Bee for 20 years.
365 Coral Circle
El Segundo, CA 90245
Test results very scientific
Soil and Plant Laboratory, Inc.
1594 N. Main Street
853 Corporation Street
Santa Paula, CA
USDA Natural Resources Conservation Service
44811 N. Date Avenue
Lancaster, CA 93534-3136
Here’s a dirt cheap (pun intended) test for soil ph that you can do yourself.
UPDATE: 7/7/09: Visiting journalist Michael Tortorello tipped us off to the University of Minnesota’s soil testing lab will test out of state samples for their regular (low) fee. It’s much cheaper than the services listed above. Their submission forms are located here.