City gardening: Should you be concerned?
No! Just follow these simple rules (and always wash your produce!)
The motivation for fresh, clean, organic food gets me out into the garden as soon as I’m off work, and often beforehand. The rewards of this lifestyle are many; the bounty of fresh, clean, organic produce is worth every drop of sweat.
Keeping things fresh and clean is one reason I enjoy growing as much of my own food as possible, as I’m increasingly aware of how difficult it is for organic farmers to maintain their high standards when surrounded by chemical agriculture. Pesticide drift, water contamination and reckless DNA hidden in airborne pollen are often finding their way onto the land of farmers working hard to provide a higher standard for their customers.
But what about those of us gardening in the city? Like the organic farmer in the countryside being assaulted by agricultural pollutants, are we also under siege from the emissions of traffic and industry, as well as our neighbor who insists on three Chemlawn treatments a year, bees be damned?
In every city, pollution is everywhere. Urban areas are often far more likely than their countryside counterparts to contain contaminated soil.
I’m growing a garden as part of my strategic solution to this mess. We urban farmers and gardeners are among the most potent revolutionaries around, quietly cultivating change and re-engineering society for a more fulfilling way of life coupled with a well-balanced pico de gallo. I need to make sure the food I produce is as healthy as possible, safe for my children, and truly part of the solution. For those of us growing food in the city, it is important we arm ourselves with the information needed to garden safely and successfully.
Detailing every possible source of soil contamination is outside of the scope of this article. Fortunately, unless you are trying to grow on previously industrial land or near a dry cleaning business, chances are a few simple precautions are all you need to take. And remember, the benefits of eating fresh produce generally far outweigh any of the risks.
While some edible plants do take up and accumulate contaminants, research shows there is minimal risk of exposure from eating plants grown in contaminated soils. The real concern is in working with the soil itself.
Organically grown or not, urban or rural— it is always a good idea to thoroughly wash produce with running water to remove any potential contamination from soil or air.
Routine soil testing for nutrients and organic matter is a good habit for every gardener to have, and helps you make informed decisions when it comes to fertilization. Testing for heavy metals is also easy to do at the same time, and the lab will help you interpret the results.
Lead is the most common residential soil contaminant, most notably because most paint in use before 1978 contained lead. Flakes of deteriorated paint often found their way into soil. Lead in gasoline was in common use until 1989. Areas of high traffic saw an increase in the amount of lead pollution from vehicle emissions.
Fortunately, lead does not leach very far from the point of initial contamination. Lead is also not a plant nutrient, so plants do not “take up” or absorb lead. The main point of danger with lead contamination is the ingestion or inhalation of lead dust.
If you have an old home, garage or other structure that you suspect has lead-contaminated soil, the best course of action is to cover the bare soil with plants or a thick layer of wood chips, as the bare soil itself is the most likely to be inhaled or ingested. The EPA recommends incorporating up to 50% compost into the soil, which dramatically reduces the concentration of lead. Top dressing with compost or mulch also helps to contain any lead dust below.
Children are the most likely to be negatively impacted by lead, so if you have a landscape that you share with children, do not leave bare soil exposed. Nature also abhors bare soil, and will go to great lengths to cover it, usually with noxious weeds. Save the children, grow some fun and interesting plants or lay down some mulch—it’s that simple.
Another common contaminant for residential urban soils is chromated copper arsenate (CCA), an inorganic pesticide used to prolong the life of lumber; decks, playground equipment and picnic tables were commonly treated. Containing chromium, arsenic and copper, it was the predominant type of wood preservative until it was banned in 2004. Older “pressure-treated” wood was almost certain to have contained this, and this type of wood was commonly specified in building codes for “ground contact” lumber. It’s often difficult to tell where wooden structures containing this type of lumber may have once existed.
Arsenic was also a common ingredient in many pesticides and other agricultural chemicals, and nearly all urban residential areas were at one point in their history agricultural.
Creosote, the material used to preserve railroad ties, poses similar risks. While old railroad ties are often useful in designing landscapes, they should never be used near areas used to produce food. The long-lasting potential for soil contamination might also be cause to consider an alternative material in your design.
Soils contaminated with CCAs, creosote, arsenic and certain heavy metals are best avoided, and one simple way to do this is to build raised beds. Use untreated lumber or other materials. Line the bottom of the bed with geotextile underlayment or other heavy duty landscape fabric to prevent the roots of plants from reaching down into the contaminated soil. Make sure to build the beds to a depth of at least 12” to allow for proper root growth of annual vegetables. Fill with clean soil and compost.
One final concern to address: air pollution. Again hearkening back to the advice of the EPA, as well as the words of common sense: Thoroughly wash all of your produce, regardless of the origins. Plants are extremely picky about what they will allow into their tissues, but they have little choice about what lands on them. Whether it’s brake dust from traffic on land or bird shit from the traffic in the air, I prefer my produce fresh and clean.
James Loomis is a full-time urban farmer, educator and permaculture hooligan.
For more information on soil science, soil amendments, plants, contaminants and their health effects: