The overgrown lots and sidewalks of California cities might not seem like a great place to seek out nutritious greens, but in a recent study published in PLOS ONE, Professor Philip Stark and his team have found evidence of a potentially untapped bounty of drought-resistant, edible weeds growing in the dense urban environments of three cities in the San Francisco East Bay region of California. Furthermore, the University of California, Berkeley research team’s findings suggest that even while soil in these environments may have higher levels of lead, cadmium, and other heavy metals, certain varieties of wild-growing greens are still safe to eat (after a thorough rinsing, that is!).
Over several months between 2014 and 2015, Stark (who is the Principal Investigator of the Berkeley Open Source Food project) and his team set out to conduct field observations, soil tests, and nutritional and toxicology tests on plant tissues pulled from three separate sites in the East Bay cities of Berkeley, Richmond, and Oakland. Over several months between 2014 and 2015 Stark and his team set out to visit various sites throughout the East Bay; each site was approximately nine-square blocks and focused on areas where residential buildings bordered busy roadways and active industrial zones. At each location the team conducted field observations and collected plant specimens and soil samples for additional tests back in the lab. In essence, the researchers were interested in testing the soil and plants from what could be considered “food deserts,” usually impoverished urban areas where it is difficult to buy affordable or good-quality fresh food due to a lack of grocery stores or markets where healthy food is offered. “According to the USDA, the areas in Richmond and Oakland are more than a mile from any shop that sells fresh produce; and the area in Berkeley is more than half a mile from such a shop,” says Stark and his team. “All have below average income, according to the U.S. Census.”
Yet all around them, Stark and his colleagues saw an overlooked food source: wild, edible weeds. Using iNaturalist (an open-source citizen science database of observations of plants and animals), Stark utilized teams of observers to help record estimates of the number of servings of edible weeds that were either “accessible” (defined as within an arm’s reach of a public space, such as a sidewalk or road) or “visible” (defined as visible and available to those with access to the property where the weeds have grown) within the chosen sites. What they found was that wild edible plants such as mallow, bristly ox tongue, cat’s ear, English plantain, wild lettuce, nasturtium, dandelion, sweet fennel, sourgrass, and chickweed, were available and visible in abundance, growing without human aid and persisting even during record droughts in California.
But how is one to know whether or not it is safe to eat the edible plants growing in these environments? To answer this question, Stark and his team collected soil samples from various sites in the cities of Richmond and Oakland (specifically, the West Oakland neighborhood), and sent the samples to a lab in order to test for the concentration of metals such as zinc, copper, arsenic, lead, cadmium, and other toxic metals present in the soil. Then, plant tissue samples were collected from locations where the soil testing had shown the highest concentration of metals, including a few samples from plants growing between patches of asphalt. The plant tissue samples were rinsed in tap water and then dried before being sent to a lab to be tested for metal contaminants. In addition, the team also had fresh samples tested for the nutritional value as well as for potential chemical contaminants (such as man-made chemicals, glyphosate, multi-residue pesticides, and oxalic acid).
When the results were in, the study found that while a few soil samples showed levels of Lead and Cadmium near or exceeding EPA limits, toxic metals detected in most soil samples were far below the US EPA maximum acceptable daily dose for children and adults. In addition, approximately 330 pesticides, herbicides, and other toxins did not turn up in soil sample tests.
Beyond safety concerns, Stark’s team also sought to investigate the potential nutritional value of wild greens sprouting up along busy roads and working factories. Pulled straight from slabs of concrete and asphalt, these wild, foraged weeds contained considerable nutritional value per serving, and in some cases even substantially exceeded the nutritional power of the mighty superfood kale. Stark and his team also compared the nutritional value of their found food to other common grocery items: “The nutrient density of the wild greens is high, and compares very favorably to commercially farmed produce. For instance, a cup of dock or a half cup of Nasturtium contains more than the adult RDA [Recommended Dietary Allowance] of Vitamin A (5000 IU). The amount of calcium per cup of mallow is almost 27% higher than the same volume of whole milk and contains 72% of the protein.”
The takeaway? While these plants weren’t cultivated on an organic farm tucked away in the bucolic pastures of California’s central valley, they appear not only safe to eat but also surprisingly nutritious compared to some of their store-bought counterparts. While this research is promising, you shouldn’t just start eating every leafy green you see growing between your front door and your office. Stark and his co-authors emphasize that they’ve only tested samples for a limited number of locations and warn that their study does not mean that all wild edible greens foraged in an urban environments are safe to eat. Still, the research plants enough seeds to make one rethink just what those pesky, resilient weeds that seem to grow in every nook, cranny, and crack of the modern landscape might have to offer.
Stark PB, Miller D, Carlson TJ, de Vasquez KR (2019) Open-source food: Nutrition, toxicology, and availability of wild edible greens in the East Bay. PLoS ONE 14(1): e0202450.
Featured Image: Ribwort Plantain (Plantago lanceolata): Philip B. Stark / iNaturalist, CC BY-NC 4.0