Tuesday, November 22, 2011

Fertilizing Green Roofs? Stop Now!

Did you know your industrial fertilizers you are spreading across your rooftop garden contain Persistent Organic Pollutants (POPs)?  Or are we denying the many silent environmental and health impacts of POPs.

Having read the article posted by @psustentavel on Twitter - click here for the article about Persistent Organic Pollutants - the imagery of 'inorganic chemical 'fertilizers across countless green roofs,  the use of drinking water for irrigation - even backup irrigation - and the reckless abandon with which we use non-native species for landscapes, including those on rooftops, made me think - in our rush to install green roofs atop buildings, are we too creating a chronic issue someone else will have to pay for?

The value of green roofs is unquestionable.  There is solid scientific data to back up claimed benefits of habitat creation, carbon sequestration, oxygen production. greenhouse gas reduction, heat island effect tempering, cleaning of stormwater, integrated pest management and so much more.

Florida Extensive Green Roof Nature Irrigated

There is no doubt about the value properly designed and maintained green roofs can bring to the Urban Core.

Green roofs can be used to support Urban Permaculture - small scale, individualized rooftop farming operations providing food, fiber and medicine to city residents.

And many urban areas around the world are moving ahead with plans to increase urban agriculture.  Singapore, for example, produces 25% of the entire city's vegetable crop within the city limits. For a fascinating look at the importance of urban permaculture  read foodsecurity.org's white paper entitled Urban Agriculture and Community Food Security in the United States; Farming From the City Center to the Urban Fringe.

Rooftops are the new frontier of real estate in many urban areas.  Cities with limited available ground level real estate have acres of open rooftops.

Vegetated and green roofs are increasing in popularity, showing an impressive growth rate trend over the past decade.  According to Greenroofs.com, public awareness of and interest in green roofs is steadily growing.

Yet in our noble rush to restore volumetric green to the urban core we hopefully will recognize the potential environmental costs associated with mass production of green roofs.  The 'One Size Fits All' approach to green rooftops will not work for the worlds vastly different ecosystems.  Sadly and reminiscent of mega-agriculture's damaging past practices, we as an industry turn to potent chemicals to fertilize, control pests and then use much needed drinking water to either irrigate or serve as backup irrigation.

Independent and craftsman-like green roof design and construction could disappear.

As with the POPs causing health issues in Pakistan and other places, our indiscriminate use of hardy invasive species, potentially toxic chemical fertilizers, pesticides and herbicides on green roofs is a Ponzi Scheme our children too will pay for.

Importantly, we as an industry have already moved far in the direction of ecologically inappropriate and environmentally dangerous green roof design.  Florida's FDEP green roof in Pensacola, Florida possesses a large drip irrigation system, backed up with potable drinking water and planted with slow-release fertilizer compounds and soil amendments.

As in hidden environmental consequences associated with corporate profitability, denial of reality is the basis of success.  Though the 'green' benefits of the FDEP green roof are often touted in the media - the fact that chemical fertilizers are applied and potentially damaging to Escambia Bay's ecosystem are hidden.

Yet FDEP is fully aware of the environmental problems resulting from POPs, fertilization and pesticide use on green roofs.  In the proposed, new State of Florida Stormwater Applicant's Handbook,   FDEP allows green roof credit for volume retention of stormwater only (no water quality credit),  and recognizes fertilizers and pesticides will be used on green roofs (why no water quality credit is given), an approach we must reject.  Moreover, FDEP is requiring the purchase and use of a 'pollution control media' made from ground up automobile tires under the green roof soil media to keep the fertilizer's nutrients on the roof.

Over time and as water evaporates, added pesticides, herbicides and fertilizers will concentrate back into the surface waters and become an issue for our children.

In the rush to add volumetric green to the Urban Core, the POP issue could easily go unnoticed.

Temper the hurry to install a green roof with the knowledge of a local native species botanist and a soils expert.  Rather than ordering large amounts of hothouse pampered plant material, find a local nursery with individual plants acclimated to the climate.

Green roofs can be crafted to add artistic, educational, ecological and ethnobotanical value.

But we must first reject the incorrect notion that green roofs must be fertilized, irrigated with drinking water and doused in pesticides.

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