chocolate skyline

Cacao “beans” drying on a rooftop in Ghana || photo by Toby Webb

This Valentine’s Day season I’d like to be as close to chocolate as possible, and consumer market trends suggest that I’m not alone.  For those of us living far from the equator, though, the main ingredient in chocolate, cacao, travels an incredible distance to reach our plates.  Cacao are seeds, often referred to as “beans,” found within football-shaped pods that grow from the trunk and branches of the cacao tree (Theobroma cacao).  The tree is native to the South American lowlands and is now propagated within rainforests throughout the equatorial tropics and sub-tropics of Central America and parts of South America, Africa, and Asia.


Agricultural rooftop use in Granada (top) + Mexican farmers drying cacao out of their chickens’ reach (bottom) || photos by The Grenada Chocolate CompanyMadre Chocolate/David Elliott

The process of deriving coco from the cacao bean is labor-intensive and is often performed by growers and plantation owners in remote areas.  Once cacao pods ripen, they’re cut from the tree and the beans are extracted.  The beans are fermented, laid on a flat surface to dry, and then generally exported to another country where they are roasted.  The roasted beans are ground to a fine powder called cocoa, which is then blended with sugar and other ingredients to produce the creamy sweetness that we’ve grown to love.

“Cacao seeds, or ‘beans,’ have to be dried after fermentation as a measure to prevent molds [and] mildews from growing on them during transport,” explains botanical scientist and cacao expert Dr. Cindy Skema.  “It is a bit of an art, though, because the beans must not be over-dried because they can become too brittle and that creates problems in processing.”  As you may imagine, naturally flat areas for drying cacao beans are a rarity for many rainforest inhabitants.  Some growers and plantation owners build structures specifically designed to dry the beans, with protective covers that are either static or slide on tracks, like a convertible roof, to protect the crop from incoming rain storms and shield the beans from insects and birds.  Others lay beans on their village’s concrete, central square, as I’ve seen myself in rural Venezuela.

In isolated instances around the world growers have been seen industriously using their rooftops as drying grounds for cacao beans.  Multiple examples exist in Trinidad, but growers and plantation owners in Brazil, Ghana, the Dominican Republic, Grenada (in the Caribbean), Vanuatu (in the South Pacific), and Mexico have also pursued the practice.  In Oaxaca, Mexico, chocolatier consultant and author Clay Gordon visited a family farm that allocated roof areas to drying cacao because this location was, “out of the reach of chickens,” he says.  Gordon explains, though, that drying cacao on roofs is not a common practice due primarily to, “the labor of getting the beans up there in the first place. Furthermore, not all roofs [in cacao-growing locations] are flat or sturdy – many of them are pitched and made of galvanized corrugated metal, which is not a good surface for drying beans.”


Cacao drying on rooftops in Vanuatu (top) + Trinidad (bottom) || photos by Zaia Kendall + Leonie Milner

Skema agrees that drying cacao on rooftops is not very common, but to her, the practice comes as no surprise.  “It makes sense,” she says, “I mean [the roof] is a typically open, available space that gets very hot and is a bit cleaner than ground level, or at least without people [or] animals walking through.”  Skema notes that around the world roofs are used to dry a variety of things, like edible plant material, meat, and clothes.

Agriculture involves not just food production, but also processing, or the preparation of crops for sale via washing, fermenting, drying, etc.  Rooftop agriculture generally evokes images of crops strictly in production, even for me, and we rarely stop to think about supplementary agricultural practices fit for rooftops.  Using roofs to dry cacao is a beautiful example of the creativity of farmers who, in all reaches of the world, have independently developed the same practice.

This Valentine’s Day, when you’re craving chocolate, pause to think about whether your indulgence spent part of its lifetime on a roof, under the sun, and what other non-production agricultural practices could occupy our rooftops.


Bletter, Nat. Email correspondance. 17 November 2015.

Gordon, Clay. Email correspondence. 18 November 2015.

Gordon, Clay. “Madre Chocolate-From The Road In Xoconusco, Chiapas.” Discover Chocolate, 7 March 2011. Web. 11 October 2015.

Skema, Cynthia. Email correspondance. 10 November 2015.

Skema, Cynthia. “Ka-Pow Cacao.” Morris Arboretum of the University of Pennsylvania. 100 E Northwestern Ave, Philadelphia, PA 19118.  Lecture.

food city scenario


Excerpt from “Fayetteville 2030: Food City Scenario” || Image by the University of Arkansas Community Design Center

What would your city look like if urban agriculture drove development? The University of Arkansas Community Design Center posed this question in 2012 when a team of designers, scientists, lawyers, and students explored what their rapidly densifying city of Fayetteville, AR would look like by 2030, the point at which the population is projected to double to approximately 140,000 residents.  The team, led by Community Design Center director Stephen Loni, used scenario planning – a speculative process that anticipates how specific decisions will shape long-term realities – to develop “Fayetteville 2030: Food City Scenario,” or Food City, as it’s better known.  This visually enticing project depicts a future Fayetteville that prioritizes food security and food localization as organizing elements of urban growth.  Food City has earned national recognition by winning multiple awards, including an ASLA 2015 Professional Honor Award, and appearing as the subject of a feature article in Landscape Architecture Magazine‘s January 2016 issue, written by EAT UP author Lauren Mandel.


Tri Cycle Farms and permaculture farmer Don Bennett || photo by Lauren Mandel

“When you’re trying farm farmers and grow growers, it’s all about accessibility,” says Fayetteville urban farmer Don Bennett, who founded Tri Cycle Farms in 2011.  Don and his flock of volunteers, many of whom are food insecure, cultivate nearly 2-acres of land in the city’s geographic center using permaculture techniques.  Don is part of a growing food localization movement in Fayetteville that focuses in large part on food equity and access.  Other local, budding establishments that help bring fresh, nutritious food to Fayetteville’s residents include Feed Fayetteville (a food security non-profit), Apple Seeds Teaching Farm (a hands-on agricultural education site), The Farmer’s Table Cafe (a popular farm-to-table restaurant) and the Fayetteville Farmers’ Market (which was established in 1973 and is now the largest producer and vendor market in Arkansas).


Excerpt from “Fayetteville 2030: Food City Scenario” || Image by the University of Arkansas Community Design Center


Excerpt from “Fayetteville 2030: Food City Scenario” || image by the University of Arkansas Community Design Center

Do you want to learn what’s on-tap for Fayetteville’s transforming food system and read more about the people behind the movement? Check out “The Next Meal” in Landscape Architecture Magazine‘s digital January 2016 issue or pick up the print edition at your local Barnes & Noble store before mid-February.

major league crops

Fenway Farms, atop Fenway Park’s Front Office || photo by Dr. Richard Mandel

The Kansas City Royals may have won this year’s World Series, but the Boston Red Sox were the real 2015 winners.  While this American League team’s game may not have been up to snuff, it’s historic stadium knocked one out of the park in April when Fenway Park representatives announced their plans to build a rooftop farm, the first in major league baseball.  Later that month Fenway Farms materialized, with its first harvest in May.  Now the weather is halting production for the year, which offers the facility’s designers and farmers time to reflect on the farm’s inaugural growing season.


Farm in October 2015 || photo by Dr. Richard Mandel

“All the stars aligned to make this project go forward, but it was ultimately Linda Henry, married to the owner of the Red Sox, who breathed life into it,” says Mark Winterer, the farm’s designer and co-owner of Recover Green Roofs, LLC in Somerville, MA.  “One-year prior to Linda’s involvement, The Red Sox contacted Recover and was interested in a Sedum green roof.  While we couldn’t find the financing to build the Sedum green roof, we were able to find the right [roof area that could support the load of a farm], so when Linda got involved, we were ready to go,” says Winterer.  Fenway Farms is located atop the stadium’s Front Office, on the third base side at the EMC Club Level.  It’s visible from both the EMC Club and State Street Pavilion Levels, but accessible to the public only during stadium tours.  Stop & Shop, Dole, Sage Fruit and Aramark financed the project.

The approximately 4,000 pounds of vegetables and herbs grown at Fenway Farms annually make their way into dishes prepared in the stadium’s EMC Club kitchen.  The stadium’s chefs, including Fenway Park executive chef Ron Abell, choose which crops will be grown each season from a master list, which are then planted in spring and summer by Green City Growers, an urban farming company that serves eastern Massachusetts.

Cucumbers did really well,” says Green City Growers CEO and founder, Jessie Banhazl, “we harvested 600 pounds of cucumbers [during the 2015] season.  Kale, lettuce, carrots, peppers, and eggplants also did well this year.” Banhazl was surprised by a unexpectedly vigorous strawberry crop, so much so that she’s amending next year’s crop plan to include more berries and fruit for Fenway Park’s pastry kitchen.


R.A.M.M. installation at Fenway Farms || photo by Mark Winterer

The farm system itself, designed and installed by Recover Green Roofs, consists of rows of modular plastic crate growing systems lined with filter fabric sleeves – called “Recover Aerated Media Modules (R.A.M.M.) – filled with 10-inches of Vermont Compost custom blended organic soil, with a Weathermatic Smartlink drip irrigation system.  The planter design closely resembles that at Higher Ground Farm, atop the Boston Design Center, designed and built by Recover Green Roofs in 2013.  “Fenway asked if we could do something similar to Higher Ground Farms,” says Winterer, “they liked the idea that it was a relatively inexpensive option, and that they could remove it if need be.”

What changes did the Fenway design include as a result of what Recover Green Roofs learned from the earlier project?  “We learned to buy prefabricated fabric liners because Higher Ground Farms found it difficult to hand make those liners using filter fabric,” recounts Winterer, “we also used individual drip emitters [within each] milk crate instead of using your typical drip line with emitters spaced 12-inches on center.”


“Beta R.A.M.M.” at Higher Ground Farm || photo by Lauren Mandel

One of the most unique qualities shared by both projects is their use of potting soil instead of the modified, lightweight green roof media that’s typically deployed in rooftop farms.  Winterer explains that, “the big take-away from Higher Ground Farm is that the milk crate allowed them to use potting soil up on a roof without worrying about it blowing away.  Vegetable plants are much happier in potting soil than engineered growing media.”  While the plants may be happy, modified green roof media is generally preferred for rooftop farms because it remains structurally stable (without breaking down or compacting) while maintaining its drainage capacity.  By contrast, potting soil decomposes, compacts, and can easily clog filter fabrics within a single season.  These properties suggest that soil replacement may be a necessary component of the Fenway Farms maintenance plan, which may be worth the hassle given the plants’ high productivity in this optimal soil environment.

What changes would the chefs like to see next year? Fewer radishes! “Radishes also did really well, which the kitchen was not happy about,” says Banhazl, jokingly, “we’ll have to pair back on how many we plant this year, they were rolling their eyes at us by the end of the spring every time we walked in with more radishes.”

financing the farm


Produce psyched about finance + encouraging you to tweet their hashtag || graphic by Lauren Mandel

Loquacious urban agriculture enthusiasts, like myself, revel in spreading the rooftop agriculture gospel.  I’ll happily talk your ear off about the countless benefits of rooftop farming, explain the technical intricacies of skyline farm design, and debate the most robust rooftop crops.  What I don’t often talk about, what most rooftop agriculture experts don’t often mention in depth, is finance, the elephant in the room.

Rooftop farmer Ben Flanner, working a farmers’ market in Brooklyn || photo by Jake Stein Greenberg

Earlier this week at Green Roofs for Healthy Cities‘ annual Grey to Green Conference in Toronto, I tackled this “elephant” head on with collaborators Ben Flanner (head farmer and president of Brooklyn Grange) and Mark Winterer (co-owner and director of operations at Recover Green Roofs, LLC).  Ben’s company owns and maintains two of the largest commercial rooftop row farms in the U.S. (totaling 2.5 acres) within the NYC region, and Mark’s company designs and builds green roofs in the Boston area, with a specialization in food roofs.  Together, we approached the topic of rooftop agriculture finance through the complimentary lenses of designer, farmer/business owner, and contractor.

Here are some of our main talking points, aimed at helping aspiring skyline farmers and entrepreneurs develop strong financing strategies.  One of the underlying messages throughout the talk was that while there are varied agricultural production methods and numerous financing strategies, no single approach is “right;” the approaches are simply different.

1| Designing with intent: The first step in realizing your vision for a rooftop farm is pinning down your primary goals.  Identifying your objectives and priorities early, while thinking about the big picture, will help you to stay focused and design with intent.  Simple questions to ask yourself are: who will grow the food?  Who will eat the food?  What yields are needed?  What scale of financing is possible?  These questions will help you select a production strategy.  Most commercial rooftop farms deploy some combination of raised beds, row farming, and/or greenhouse hydroponics.  You should consider how to best juggle construction costs with material integrity.  For example, untreated white pine is an inexpensive raised bed material, but it will degrade quickly and need to be replaced.  Cedar is much more expensive, but exhibits a much more long-lasting material integrity.  A greenhouse could last a lifetime.

2| Financing the farm: Most North American rooftop farms are financed using a hodgepodge of approaches.  These financing strategies often include some combination of loans, incentives (federal, state, or local), personal capitol, investor equity, parent company partnership, long-term purchasing agreement, and crowd-funding.  Fleshing out your multi-faceted strategy within your business plan is paramount.  During this process, allow your project goals, mission, and vision to drive your strategy.  In addition to making your business run more smoothly, a thoroughly developed financing strategy that acutely targets a goal will be more attractive to investors than a half-cooked plan.  Be specific, yet conservative, about cost and revenue projections.

High-initial investment production at Lufa Farms || photo by Lufa Farms

3| Profits and payback: Each agricultural production method mentioned above – raised beds, row farming, and greenhouse hydroponics – exhibits pros and cons.  The main financial consideration in selecting a method is whether you want a high cost, fast payback or low cost, slow payback approach.  Again, there is no “right” approach; there are simply different strokes for different folks.  When considering payback, research whether your city or state offers the following incentives for your rooftop farm: tax credits, tax abatements, subsidies, construction rebates, stormwater fee reductions, FAR bonuses, expedited permitting.  Also consider that full-coverage rooftop row farms will increase the life of your building’s waterproofing membrane by 2-3 times, which presents additional long-term savings.  A 1-2 storey building could additionally exhibit energy savings.

Low-initial investment method at Higher Ground Farm || photo by Maureen White, courtesy of Higher Ground Farm

4| Personnel dance card: Staffing should be organized to meet your farm’s needs.  Brooklyn Grange’s logistics, operations, and sales, for example, are run predominantly by the farm’s founding members.  Farms built by Recover Green Roofs, by contrast, are typically owned by a parent company (such as Whole Foods Market or Fenway Park) and farmed by a partner company, Green City Growers.  Another approach, deployed by Eagle Street Rooftop Farm, involves one head farmer aided by apprentices, interns (receiving college credit rather than a salary), and volunteers.  Lufa Farms – a leading Canadian greenhouse hydroponic company – has a staff of over 50, organized into sub-teams for management, production, outreach, etc.  Many of Lufa’s employees actually focus on developing technology, rather than on traditional production.

5| Innovative use of technology: One of the biggest differences between the sales approaches of rural and urban rooftop farms is the use of technology.  Most rooftop farms rely on websites, blogs, and social media (Facebook, Twitter, Instagram) to build their brand and their audience/customers.  One particularly innovative use of technology is Lufa Farm’s Online Marketplace, which allows the farm’s members to customize which farm goods they’d like each week. The goods are boxed and sent to local drop-off points around Montreal.

6| Replicating success: Your long-term financing strategy should consider one last key variable that many rooftop farming companies are already addressing: scale.  Many farms choose to gain rooftop acreage through networked rooftops.  If you want your rooftop farming company to be profitable, you’ll need to crunch some numbers to determine how big your raised beds, row farm, or greenhouse needs to be.  Keep in mind that launching multiple farms should be a phased approach, so keep calm and farm on!

EAT UP turns two!

Roof-to-Table Launch Event, 2013 || photo by Jane Winkel

It’s hard to believe, but this week EAT UP | The Inside Scoop on Rooftop Agriculture turns two!  My little bubelah is so grown up.  Since EAT UP’s publication by New Society Publishers in spring 2013, urban farmers and gardeners across the world have been able to get their paws on the first full-length book about rooftop food production.

Rooftop farmer Annie Novak at Eagle Street Rooftop Farm, 2010 || photo by Lauren Mandel

Some historians believe that rooftop agriculture dates back to 600 BCE Iraq, so how much could have possible changed in the past two years?  As it turns out, a groundswell has emerged.  When writing the first draft of EAT UP back in 2010, I posed the question of whether rooftop agriculture is viable.  At that time, little published information existed on the subject, aside from a handful of magazine articles, so I began conducting interviews with the budding industry’s leaders.  Annie Novak, Viraj PuriMohamed Hage, and Ben Flanner – all titans in the rooftop agriculture movement – were some of my first interviewees.  These urban farmers and CEOs revealed that the question of viability was moot; rooftop agriculture is real and it’s happening.

In response to the rapidly blossoming North American rooftop agriculture movement, drafts two through four of the book increasingly shifted focus from viability analysis to how-to.  Draft five (which was ultimately published as EAT UP) functions as a comprehensive resource featuring over 15 inspirational projects and offering readers the tools they need to pursue rooftop food production at three scales: gardening, farming, and industry.

During five short years of manuscript re-writes and post-publication, so many new rooftop farms and gardens have emerged that it’s become wonderfully impossible to keep track of each project.  The rooftop agriculture movement has organically reached it’s twining shoots around balconies and fire escapes, up walls, and across school and spanning warehouse roofs.  It’s everywhere.  In fact, a recent National Gardening Association report found a 17% increase in households with edible gardens during the past five years (from EAT UP’s first draft to now), which includes more than 13 million millennials.  The majority of millennials live in cities, so it’s conceivable that many of these gardens occupy urban settings.  Oh how the tide has changed!

Geographically speaking, where has the greatest increase in rooftop farms and gardens emerged?  As the birthplace of North America’s commercial rooftop agriculture industry and a city where space is at a premium, it’s no surprise that New York City makes the cut.  Chicago and Toronto’s green roof bylaws and favorable urban agriculture regulations similarly lend themselves to industry growth, so there’s no surprise there.

Ledge Kitchen & Drinks, 2012 || photo by Patrick Rogers Photography

And then there’s Boston.  Between you and me, Boston’s leadership in the rooftop agriculture movement comes as an utterly wonderful surprise, given the city’s cold climate and moderate density.  Many of the city’s high profile projects were designed and built by REcover Green Roofs, based in nearby Somerville, MA.  The company’s first food roof was built in 2010 atop a restaurant called Ledge Kitchen & Drinks, with later installations above the Boston Design Center and Whole Foods Market Lynnfield.  Just this week REcover Green Roofs’ newest food roof, Fenway Farm, began production at Boston’s own Major League Baseball stadium, Fenway Park.  Stay tuned for an EAT UP Blog post on this farm soon.

How will the rooftop agriculture movement mature by EAT UP’s next few birthdays?  That’s entirely up to you.  Climb up there and get started!

Philly’s tipping point

Philadelphia Mayor Michael Nutter at the 2015 GSK IMPACT Grant award ceremony || photo by Lauren Mandel

On March 19th ten players in Philadelphia’s urban farming community received a whopping $5 million grant award aimed at kickstarting healthy eating, exercise, and community building opportunities for local teens.  The IMPACT Grant, awarded by GlaxoSmithKline (GSK) and administered by The Philadelphia Foundation, provides local non-profits with financial resources to help disadvantaged youth live healthier lives and contribute to healthy communities.  The grant and GSK’s annual IMPACT Award targets communities surrounding GSK’s three US campuses, in Philadelphia, St. Louis, and Denver.

Top to bottom: Mayor Michael Nutter, Joie Kathos dancers, Philly public school student chef, Greener Partners || photos by Lauren Mandel

This year’s award winner, Get HYPE Philly, is a consortium of ten Philadelphia-based non-profits led by The Food Trust, a national leader in nutritious food access, founded in Philadelphia.  The partnership organizations project that their coordinated efforts will reach over 50,000 teens during the next three years through the following areas of focus:

“Eating healthy food is not a fad or a trend, it’s a lifestyle,” said Abdur Peay, a Thomas Mifflin School 7th grader, when speaking at the podium of the IMPACT Grant award ceremony.  “I’d like to bring HYPE to other cities and states, maybe go global.”  The youth’s words elicited cheering from the crowd of students, activists, executives, and media gathered at the Free Library of Philadelphia for the ceremony.  Philadelphia Mayor Michael Nutter followed Peay and fellow 7th grader Josiah Johnson with his own remarks, praising GSK’s investment in the health of young Philadelphians.  “Our administration has made this effort a priority in promoting healthy living,” said Nutter, before enthusiastically putting on a HYPE baseball cap.

Many of the Get HYPE Philly partnership organizations plan to expand their existing programming to target teens ages 12-18.  Liz Fitzgerald, culinary literacy specialist for the Free Library of Philadelphia, says the grant funding will enhance the library’s teen programming in the Culinary Literacy Center (which teaches literacy through cooking in the library’s new demonstration kitchen) and bring nutrition education to teens at library branches around the city.  Justin Trezza, executive director of Norris Square Neighborhood Project, is equally thrilled about the grant award and explains, “We’ve been waiting for something like this for a long time.”  Trezza’s organization serves mainly youth, 70% of which identify as Latino or biracial. “We don’t see gardening as purely producing food, but also as connecting people back to their cultures and heritage. With this [grant] we’re going to be hiring new staff, building a greenhouse, building a mobile farm stand to interact with out community members and offer them produce at a very, very affordable price.  We sell everything for a dollar.”

The $5 million IMPACT Grant award could be the tipping point in Philadelphia’s ongoing efforts to address food equity.  The award will be issued incrementally from 2015 through 2017, but Get HYPE Philly’s leaders plan to use the award as a springboard for future initiatives.  Yael Lehmann, executive director of The Food Trust, explained that, “We want to sustain this beyond the three-year period and that’s going to be an important part of our work that we’re going to start today, day one.”  Food access activists in Philadelphia and around the country will watch to see if this unique collaboration offers the muscle that’s needed to elicit lasting change and breed a new generation of leaders.

Seventh graders Abdur Peay and Josiah Johnson addressing the crowd || photo by Lauren Mandel

hungry for acreage


Gotham Greens co-founder + CEO Viraj Puri || video frame from Made in Brooklyn

We’ve been keeping an eye on Gotham Greens since the rooftop farming pioneer opened its first commercial greenhouse in 2010.  The Brooklyn-based company’s 15,000 square foot (0.3-acre) flagship farm, in Brooklyn’s Greenpoint neighborhood, yields 100 tons of leafy greens annually atop a warehouse building.  In 2013 Viraj Puri, the company’s savvy co-founder and CEO, struck a deal with Whole Foods Market to open a second rooftop greenhouse – 20,000 square feet (0.5-acre) – atop the supermarket’s Gowanus, Brooklyn store.  This year Gotham Greens plans to open another hydroponic rooftop farm in Jamaica, Queens, which will bring the company’s New York City acreage to 95,000 square feet (2.2-acres)!  Who would have guessed that this scale of urban cultivation was possible?

Rooftop farmers || video frame from Made In Brooklyn

“In cities we don’t have a lot of arable land, we don’t have a lot of fertile soil, but one vastly underutilized resource we do have is unused rooftop space,” said Puri in a November 2014 episode of TechCrunch TV’s Built in Brooklyn.  The CEO and his co-founders Eric Haley and Jennifer Nelkin Frymark have succeeded in meeting the local demand for fresh, responsibly-produced food using sustainable agriculture techniques.  Rainwater harvesting, re-circulating hydroponics, integrated pest management (IPM) and photovoltaics are just a few of the tools the team deploys to bring viable urban agriculture to New York City.

Rooftop basil sold downstairs at Whole Foods Market Gowanus || video frame from Made In Brooklyn

Which other cities contain building stock large and strong enough to support commercial-scale hydroponic greenhouses?  Many older cities like Philadelphia, Pittsburgh, San Francisco and of course Chicago (which is slated to receive a 75,000 square foot Gotham Greens rooftop farm for a new Method Products factory) fit the bill.  These are cities in which retrofit projects are likely to continue appearing.  In terms of new construction, it’s likely that companies beyond Whole Foods Market and Method Products will consider integrating rooftop farms into designs for future buildings.  Row farms may be considered for these new construction projects, but if high, predictable year-round yields are a priority, it’s likely that hydroponic greenhouses will be utilized.

Let’s keep an eye on the sky in our own cities to see what skyline infrastructure blossoms in the seasons to come.  And remember, if you see rooftop produce at a market near you, be sure to support your local skyline farmers by buying their greens!

ruminating on rain barrels

Herb pruning at Eagle Street Rooftop Farm || photo by Lauren Mandel

Winter is the perfect time for gardeners and farmers to rest, plan for spring planting, and investigate big questions that sprouted during the past growing season.  My big question this winter: Is it safe to water edibles with roof runoff?

As a green roof designer I regularly work with architects and building owners to select waterproofing membranes for large green roof projects (generally 5,000 square feet to several acres in size).  We discuss the pros and cons of each waterproofing material, such as cost, ease of install, and compatibility with leak detection technology.  What we do not discuss is whether it’s safe for water flowing over the waterproofing to be collected for crop irrigation.  Why don’t we discuss this?  Because until recently the simple answer was, “not a chance!”  Waterproofing (like PVC, TPO, hot liquid-applied rubberized asphalt, and even asphalt shingles) contains toxic elements and compounds that leach into runoff.  Watering crops with this contaminated water douses your food with toxins like chromium, copper, zinc, cadmium, and lead.  Pathogens like coliform bacteria and Escherichia coli can also enter the water from rooftop bird droppings.

Home rooftop gardening in West Philadelphia || photo by Lauren Mandel

For decades, though, homeowners have directed runoff from roofs into rain barrels to irrigate ornamental and edible plants.  In cities, rain barrels are often located on balconies (for watering rooftop edibles), back patios, or near front stoops.  Rain events fill the barrels, then water is released through a spigot or into a gravity-fed hose or drip irrigation system.  Have these gardeners been poisoning their families?

New information suggests that using roof runoff to irrigate edibles may be A-OK, with a few caveats.  A January 7 article by Lisa Stiffler in Sightline Daily – a digital publication by Seattle sustainability think tank, Sightline Institute – summarizes the findings of three recent scientific studies that investigated this very issue.  The first is a Journal of the NACAA article by Haberland, Bakacs, and Yergeau (2013) that monitored toxins (lead, zinc, coliform bacteria, E. coli, and polycyclic aromatic hydrocarbons) in six urban and six suburban rain barrels, supplied by runoff from asphalt shingle roofs in New Jersey.  The study found that, left untreated, the water contained levels of E. coli exceeding that recommended for crop irrigation by the U.S. Food and Drug Administration.  The second highlighted study is a Washington State Department of Ecology publication by Winters, McCall, and Kingfisher (2014), which studied toxin concentrations in runoff over time as waterproofing materials whether.  Researchers monitored toxin levels (arsenic, cadmium, copper, lead, zinc, and organic compounds) in runoff from 18 constructed roofing panels during an 11 month period.  The study finds that:

Harvesting home rooftop herbs || photo by Lauren Mandel

Across the 20 rain events, [Washington State Department of Ecology] found that asphalt shingle, built-up, modified-built-up, TPO without brominated flame retardant, concrete tile, and untreated wood shingle roofing materials did not release elevated levels of the metals or organic compounds evaluated in runoff.

The study includes several recommendations for assessing the roof condition and its runoff, which are relevant to rain barrel use.  The third study is a PLOS One article by Tom, Fletcher, and McCarthy (2014) tested heavy metal uptake by French bean (Phaseolus vulgaris), kale (Brassica oleracea var. acephala), and beetroot (Beta vulgaris) in Melbourne, Australia.  Researchers watered the crops for 11 weeks with synthetic stormwater then tested for elements (cadmium, chromium, lead, copper, and zinc).  The study found that lead uptake was most significant, but some crop varieties contained higher concentrations than others.  For example, kale and beet roots contained lower metal concentrations than French beans and beat greens.  The study recommends being selective about crop types and turning soil regularly when watering crops with roof runoff.

Suggested Guidelines when Watering Crops with Roof Runoff*

1| Be selective about the roofing material: Do not water crops with runoff from treated wood-shake roofs; roofs treated with chemicals to kill moss, algae, or rot; roofs with zinc strips; copper roofs; or roofs with copper gutters.

2| Don’t collect the “first flush”: Divert runoff from the first few heavy storms after a dry spell away from crops, into the storm drain.

3| Add bleach: Rutgers researchers recommend adding approximately one ounce of household unscented chlorine bleach to 55 gallons of water to kill the bacteria, then waiting 24 hours before watering.

4| Water the soil, not the food: Some soil microorganisms are able to break down certain toxins.  Allowing these microorganisms to come in contact with the water before the plants do may decrease soil contamination.

5| Wash produce: Washing home-grown fruits, veggies, and herbs grown with harvested rainwater can help remove surface contaminants.

6| Clean the rain barrel: Rinsing the rain barrel on occasion can help remove particulate and bacteria.  Some recommendations include mixing 1/8-cup chlorine bleach with five gallons water, then rinsing the barrel clean with municipal water.

* These guidelines are included in the Sightline Daily article referenced above, and are not expressly recommended by EAT UP, LLC.  It is each gardener and farmer’s sole responsibility to decide whether or not to water edible crops with rooftop runoff.  Local and national guidelines should always be adhered to for the protection of human health.