I could see it so clearly. Our uninspired little 10' x 20' patch of mostly-dead crabgrass in front of the house transforming into a lush garden overflowing with herbs and vegetables.
Let me back up. After too many seasons of casually planting tomatoes and peppers only to watch them wither under my neglect, I signed up for the nearby Grow LA Victory Garden class. The class is great - a four-session crash course to help get your vegetable garden up-and-running. And as any gardener knows, everything starts - and ends - with the soil.
Since we rent an old house on a moderately busy street, I thought it wise to send a soil sample in for lab analysis. $80 and one week later, the results came back.
"The soil contains high levels of lead... Use of the soil for vegetable production is not recommended."
%!$!#.
But after a minor freak-out, I had a conversation with a Master Gardener and spent a whole lot of time researching on the internet. Here are some of things I learned:
- Soil contaminated with lead and other heavy metals is fairly common in urban areas. Soils in the Bay Area, for example, have average lead concentrations of 300-600ppm - ours measured 600ppm.
- Old house paint is the biggest culprit. If your home was built before 1978 when leaded paint was banned, there's a good chance it was used. The paint gets old, dries, flakes, and collects in the soil.
- Car emissions, before leaded gasoline was banned in 1986, is another major source. Plots close to busy streets are more susceptible to contamination.
- Lead is most prevalent in the top few inches of soil, especially if it hasn't been disturbed in a long time.
So what can be done?
Cover up exposed areas
Use mulch, sod, landscape fabric, fresh soil. The idea is that you want to keep any bare soil covered and prevented from getting blown around, munched on by youngsters*, or tracked into the house.
Replace contaminated soil
Dig up the old stuff and replace it with uncontaminated soil. Sounds great in theory, but not only is this costly - one site quoted costs around $30k for 1000 sq. ft. - it's not guaranteed to work. My Master Gardener teacher told us a story of a women who paid a ton of money to have her whole yard replaced, only to find that the "new" soil tested just as high in lead.
Natural remediation
Adding organic matter raises the soil pH and binds lead, making it less available for plants to take up through their roots. Regularly till compost, manure, organic fertilizers, organic mulches into your soil. Be careful not to breathe in dust and dirt particles as you do, though. The lead will never go away, but over time it will get more or less neutralized.
Practice safe planting
Depending on the lead concentration, you can actually still plant vegetables in contaminated soils. Certain varieties like herbs, leafy greens, and root crops you'll probably want to avoid. But the biggest risk isn't ingesting lead through the plant itself, it's more the contaminated soil that adheres to the surface of the vegetables. Wash well before eating. Here's a good little handout from UC Agriculture and Natural Resources on the topic.
Build raised beds for herbs and vegetables
If you want to play it safe, build some raised beds on top of the bad stuff, fill it with fresh soil, and plant all of your herbs and vegetables inside.
After all that, what did we decide to do?
For our herbs and vegetables, I built us a 4' x 8' raised bed. I covered all the exposed soil with mulch, and sometime over the summer I'll start the slow process of organic remediation.
Sure the leaded soil forced us to adjust, but the dream lives on!
Stay tuned...
* As a precaution, we had the kids blood tested for lead. Thankfully, the results were negative.