Edible urban weeds found to be safe, healthful, abundant — and they’re free

“Wild greens” is the researchers’ term for what many among us might reflexively call “weeds,” ranging from the familiar dandelion, chickweed and sweet fennel to the more obscure cat’s ear and bristly ox tongue.

If you’ve ever considered picking backyard dandelion greens for your salad, or even if you haven’t, you may be intrigued by a recent research paper from the nexus of nutrition, food security and the urban foraging trend:

  • Wild edible greens harvested in industrial, mixed-use, and high-traffic urban areas in the San Francisco East Bay area are abundant and highly nutritious.
  • Even grown in soils with elevated levels of heavy metals, tested species were safe to eat after rinsing in cold water.
  • Wild greens could contribute to nutrition, food security, and sustainability in urban ecosystems.

“Wild greens,” of course, is the researchers’ term for what many among us might reflexively call “weeds,” ranging from the familiar dandelion, chickweed and sweet fennel to the more obscure cat’s ear and bristly ox tongue.


(Why people so often name edible wild plants after animals or their parts — think lambs’ quarters, cattail, pigweed — is a subject not addressed in “Open Source Food: Nutrition, Toxicology, and the Availability of Wild Edible Greens in the East Bay.”)

The paper grew out of the Berkeley Open Source Food project, which for several years has been both investigating and promoting the virtues of wild greens from urban forage grounds; so far, it has “accumulated 631 observations of 52 species” in Berkeley, Oakland and Richmond.

Though the new paper has not yet been peer-reviewed or published officially in a journal — it’s on the Cold Spring Harbor Laboratory’s preprint server biorXiv — the work strikes me as a modestly scaled, transparent and highly plausible effort in statistical analysis.  Also, a cool idea.

The principal author is Philip Stark, an associate dean of math and physical sciences at the University of California-Berkeley and a former director of the statistics department there. On his own time, Stark is also an enthusiastic urban forager and a founder of Berkeley Open Source Food.

This project, whose board of directors includes the legendary restaurateur and sustainability advocate Alice Waters, favors the promotion of inner-city food-gathering as it works:

[T]o create a supply chain and a market for wild and feral edible plants, reduce food waste, increase farm biodiversity, increase resilience, reduce erosion, improve farm yields and profits, reduce environmental toxins, improve nutrition, and provide interesting, delicious ingredients for consumers and chefs. We map the availability and seasonal abundance of wild and feral edible plants.

We advocate public policy that increases the amount of free, fresh nutritious foods in cities, by stopping the use of herbicides on public lands and allowing foraging of invasive species on public lands; and by promoting the design of parks and public spaces that provide food and habitat for wildlife.

A newer side of foraging

Foraging hasn’t been a primary source of food for Americans since pioneer times, but as a recreational and culinary pursuit it seems to have maintained a small, robust following with occasional surges in popularity, often associated with publication of a new handbook — Euell Gibbons’ “Stalking the Wild Asparagus” (1962) being perhaps the standout.

I received Sam Thayer’s fine 2006 guide, “The Forager’s Harvest,” as a  gift shortly after moving to Skunk Hollow, and it moved me to poke around my new rural neighborhood for ramps, rose hips, watercress and grape leaves.  Still, I didn’t think much about foraging in cityscapes until I ran across Ava Chin and her book “Eating Wildly,” which capitalized on her popular “Urban Forager” column for the New York Times (and sent me off in search of sumac to make a tart, claret-colored autumn beverage you couldn’t buy if you wanted to).

To judge from magazine articles and new book titles (plus the occasional research paper), interest in specifically urban foraging seems to be growing among city-dwelling culinary adventurers and also among activists who promote the activity for reasons ranging from strengthening constituencies for ecological stewardship to enhancing food security for the inner-city poor. (The freegan and prepper movements appear to expanding participation, too.)

See, for instance, last year’s fairly famous study from the Johns Hopkins Center for a Livable Future that examined the habits and viewpoints of more than 100 Baltimore foragers who gather significant portions of their food from parks, residential neighborhoods and corporate campuses. An account in Civil Eats last February noted that the trend has bumped up against legal barriers in places like Chicago, where an elderly and low-income forager was fined for picking dandelions, and Seattle, which relaxed its rules on fruit- and nut-gathering in public forests.

A persistent question about plucking food from city soils, however, would seem to be: Is it really safe to eat plants that grew in a toxic stew of industrial pollution?

This is the issue that Stark and his team confronted squarely in the “food deserts” of Berkeley, Oakland and Richmond, so called because high-quality fresh greens are hard to find at affordable prices.

Picking other people’s weeds

Their geographic focus is manageably narrow — three sites of about nine square blocks apiece — and so is the nutritional analysis of just six species:  chickweed (Stellaria media), dandelion (Taraxacum officinale), dock (Rumex crispus), mallow (Malva sylvestris), nasturtium (Tropaeolum majus) and oxalis (Oxalis pescaprae).

Researchers used the smartphone app iNaturalist to mark the locations and estimate the available food volumes of the plants, measured in half-cup servings, before taking samples, which is where the whole idea of picking weeds that might belong to somebody else gets a little tricky:

Observers (faculty and students at the University of California, Berkeley) estimated the number of “visible” and the number of “available” servings. “Visible” servings are those available to a person with legal access to the property. “Available” servings are those within an arm’s reach of a public right-of-way, such as a sidewalk or road.

Nutritionally speaking, the sampled greens were standouts; they outdid supermarket kale on a number of conventional measures (higher in fiber, protein and carbohydrate content, lower in fat; higher in vitamin A, calcium, iron and phosphorus). Kale held a slight edge on vitamin C.

Considering that the plants grew in heavily polluted soils — some were plucked from cracked asphalt — the researchers wanted to measure their uptake of lead, arsenic, chromium and other substances known to pose health risks.

Emphasizing sites where the soil tested highest for contamination, they gathered and rinsed greens from nine species before sending them out for lab analysis. In virtually all cases, the samples tested well below the U.S. Environmental Protection Agency’s threshold for concern if consumed in plausible quantities. A narrow exception was the cadmium content in the wild lettuce Lactuca serriola.

“While it is hard to imagine someone eating 100 grams per day of L. serriola (because it is intensely bitter),” the paper says, doing so would reach the recommended daily maximum intake for a 150-pound person, and exceed it for smaller folks.

Even more surprising, perhaps, was that a similar sampling/testing routine found no detectable residues of pesticides or PCBs in the foraged greens. Which I suppose might make them preferable to store-bought kale, if it was conventionally grown.

All the food that’s not for sale

It’s hard to say whether these findings will prove important or merely interesting.

The paper makes no lofty claims for its own significance, although it notes that official federal estimates of “waste-adjusted availability of vegetables in the U.S.” — that is, harvested volume less losses in processing — work out to about 1.72 cups per capita per day, significantly short of the recommended dietary share of two to three cups. Theoretically, at least, foraged greens could contribute to closing that gap.

Nor does it make claims for the culinary wonders of wild food, although for me it inevitably recalled Euell Gibbons as indelibly rendered by John McPhee in a 1968 profile, still available online. McPhee explains that “Stalking the Wild Asparagus” began as a novel drawing on Gibbons’ foraging triumphs,

… a whimsical romance about a poor schoolteacher who gives up his profession, buys rural land, builds with his own hands a home made from native materials, and creates the impression that he is a millionaire by purchasing a dinner jacket from the Salvation Army and inviting professors and potentates to black-tie banquets at tables laden with sunfish caviar, cattail wafers, pickled top bulbs of wild garlic, wild-cherry olives, wild-grape juice, blueberry juice, dandelion wine, sautéed blue-eyed scallops, crappies cooked in tempura batter and served with mint and sassafras jellies, daylily buds with pasture mushrooms, sautéed oyster mushrooms, buttered dandelion hearts, buttered cattail bloom spikes, wild asparagus, scalded milkweed buds, wild salads (made from Jerusalem artichokes, ground-cherries, wild mustard, watercress, wood sorrel, purslane, and greenbriar under wild-leek dressing), hot biscuits of cattail-root flour, Mayapple marmalade, chokecherry jelly, dandelion-chicory coffee, candied mint leaves, candied wild ginger, wild cranberries glacés, candied calamus roots, hickory-maple chiffon pie, and sweet blackberry wine. …

Gibbons’ interest in wild food suggests but does not actually approach madness. He eats acorns because he likes them. He is neither an ascetic nor an obsessed nutritionist. He is not trying to prove that wild food is better than tame food, or that he can survive without the assistance of a grocer. He is apparently not trying to prove anything at all except that there is a marvellous variety of good food in the world and that only a modest part of the whole can be found in even the most super of supermarkets.

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The Stark paper can be read and downloaded here without charge.

Comments (1)

  1. Submitted by David Markle on 09/06/2018 - 11:17 am.

    Nevertheless I’d suggest washing urban greens–including garden greens–with warm vinegar water or warm water with a little detergent. Adjacent or nearby soil lead levels can be very high.

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