April 21, 2014
Just got back from a short trip to my old stomping grounds, Washington DC to help my daughter and son in law plant their first garden in their new home. I dug up and bought some hebs from my garden and then we went on a shopping spree at their local nursery for some good soil, more plants and all the other stuff new gardeners need. But, a few days before, I got a disappointed e-mail from my daughter saying she had done a soil test and found LEAD!! She did some quick investigation, but it confirmed what I knew--all soil has some lead...urban gardens, however, border on toxic levels of 500ppm or more. Should city folks grow their own foods? Is it worth the risk? Should they belong to CSAs?
The answers are: yes, yes, yes!!
While lead levels are high in most city soil due to old paint, construction, car exhaust, etc., most of it does not make it into the food you grow....depending upon the type of plant and the parts you eat.
Many weeds and "invasive" plants make it their job to remove toxins, including lead, from the soil. This is called "Phytoremediation". There is new science surrounding this aspect of plant culture and their ability to clean contaminated soils and water (which is why we heard the recent caution concerning eating too much rice, since much of the water where it is grown is no longer pristine).
Great!! But then, does that mean the plants are unsafe to eat? The general consensus currently, is that most of the lead gets bound in the roots of perennials--leaving no or extremely low levels of lead in the plant. So, if you are eating herbs, rhubarb, asparagus type plants, you are probably safe. Lead does not survive into the FRUITS of plants--so cukes, squash, berries, fruit trees, peppers, tomatoes, corn are safe enough. But, if you want to grow carrots, radishes, beets or any other root crops and tender leafy, annual veggies and herbs like basil, lettuces, spinach, then use planter boxes appropriate to the depth needed to grow specific crops. It may be a good idea to replace the planter soil every year depending upon lead levels when you test each spring. To be absolutely safe, removing 2-3 inches of topsoil and replacing it would be helpful, but depending upon the source of the lead, some will return and not many people will repeat that chore every few years.
Plus--where are you going to dispose of contaminated soil? Growing plants in bad soil cleans it--so don't be too tidy in your weeding and maybe plant more ground covers. If you are exremely worried, you can do your entire garden in raised beds--but again, testing every year to make sure new lead is not building in that soil
Depending upon your urban garden space, grow what you can-- in the safest place and then use a local CSA to complete the variety and amounts you need for daily eating and canning. Keep in mind, most of us have no idea about the soil our food is grown in, or the amounts of pesticides/herbicides used and remaining in what we buy. This is not to say we should be lax and not be diligent in sourcing your food, but you may also be amazed at what is in all--even organic soils --that doesnt sound so good. We live with toxins all the time--it is the levels we need to concern ourselves with. However, we also need to do a bit of research to see how nature sometimes provides for problems--in this case, by sending in "nuisance" weeds to clean our dirty soils and still clean our air as well? Pretty nifty. Respect your weeds! They heal us.....and our environment!!