Pop culture's interpretation of "green" urban landscapes have a tendency to draw a literal representation of a more sustainable city. These "Garden City" visions can include plants growing from virtually every spatial nook and cranny possible. With flowing strands of climbing plants scaling facades and trees not only lining the streets, but poking out of sky gardens stories off of the ground, the idea of a more environmentally responsible cityscape is often presented to the public as being the result of the integration of flora and fauna.

While incorporating foliage and creating micro-climates carry a number of benefits, a truly green city has to revolve around the integration of systems to help it emulate a natural ecology. Plants should be treated as one component of a network of sustainable efforts in order to be properly utilized. This vision is not really "wrong" as much as incomplete and runs the risk of misleading people into thinking that making cities sustainable is as simple as adding plant life. There is no real solution that involves only planting our way to stewardship.

The Source of the Garden City

The notion of a garden city is not new. With icons as old as the Hanging Gardens of Babylon, the introduction of heavily planted cities has tried to capture the impressive nature of constructed urban density and scale but soften it into a picture of the natural landscape. We associate planted landscapes with clean water, clean air and less noise. The attractiveness of the imagery is an attempt at trying to get the best of both worlds. The concept is certainly an emulation of the possibilities of cities as they were imagined by legendary landscape architect Frederick Law Olmsted that designed numerous parks across the U.S. and Canada including New York's Central Park. Most of Olmsted's career revolved around weaving parks and echoes of natural spaces into the urban fabric.

A number of architects have tried to hazard an attempt at integrating the polar opposites of rural and urban environments. Frank Lloyd Wright's scenic Broadacre City plan was built around the notion of an agrarian community integrated with its natural surroundings where every resident was given an acre of land to live. Depictions of life there had pastoral backdrops with more farmland than buildings and personal hovering vehicles dotting the horizon. Ironically, the design was markedly unsustainable in its vision. The city was not really a city at all. On the contrary, the plan was essentially a more rural incarnation of suburbia with its mobility built on the backs of the automobile and devoid of all the inherent sustainable opportunities that come with density.

Decades later, architect Emilio Ambasz has crafted a large portion of his design practice around the infiltration of planted space into the city. The title page to his firm's website proudly displays "green over the gray" as a banner of the mission in building design that culminated to the iconic Prefectural Hall in Fukuoka, Japan. Containing 1 million square feet, the building sits beneath a series of tiered, planted roofs to allow for the surface of an existing park to peel upwards from the street and create a cascading green waterfall over the structure.

Behnisch's design for the Daimler Headquarters pulls a planted gardens into the image of the building

As we get closer to the present, these examples grow in frequency. Behnisch Architects has consistently integrated plant life into their designs like a rendering of their new German headquaters for Daimler AG. The modern expression of clean glass is filled with skygardens inserted into the volume. A notion of sustainability becomes unmistakable—unsurprising for a car company in need of re-branding itself in the image of sustainability. The School of Art, Design and Media at Nanyang University goes a step further with its pair of undulating forms reminiscent of natural hills. Designed by CPG, the building's continuous green roofs rise from the ground and return just as gently.

These buildings unquestionably succeed in convincing the public they are green projects, but giving a buildings a biological hairdo does not a green city make. If it looks like you can scrape the greenery off without changing the building then you most likely actually can. A former employer referred to these tactics as "green eyebrows", "growies" or a "growhawk."

A Place for Trees in the Concrete Jungle

Without question, greenery can play an important role in curbing the negative effects of urban life. I do not think many designers or planners exist that would lobby against the presence of street trees. They keep the city cooler in the summer. Their roots help mitigate storm water and their canopy supports microclimates for urban wildlife. Green roof systems go one step further. In addition to the benefits above, these layers of growing medium can drastically reduce urban heat islands in the summer while providing year-round insulating value to the buildings beneath them–even in as little as 5 inches of depth.

At the same time, it is much more realistic to think of these accomplishments as compliments to other systems rather than replacements. Sure, trees do help clean the air but our new filtering capabilities in building mechanical systems can do it to larger volumes in less time. With 95% particulate filtration, buildings like One Bryant Park actually exhaust air that is cleaner than the air they are taking in. Plants do help with storm water surges by absorbing rain water and releasing it slowly over the following days, but rainwater collection tanks can gather every drop of rain on a site and use it to flush toilets or run cooling towers.

The Green City

A city is a complex network of interconnected functions, so making a sustainable city requires us to interface with as many of them as we can and search for ways to achieve a degree of stasis. Solutions that are skin deep will end up doing little to address the full breath of energy and resources that are needed to keep cities in motion. Like an ecosystem, a successful sustainable model hinges on identifying the opportunities to link both waste streams and resource streams to new methods of utilization.

Early futurist designers took the advances we had made with industrialization in the first half of the twentieth century and used them to hypothesize visions of a metropolis that grew from maximizing the efficiencies of mechanized production. Antonio Sant'Elia was well known for his images of the "Citta Nuovo", a future city that depicted a dense urban fabric linked by systems of mature infrastructure. Though created in an era where conservation or sustainability were not goals to temper unbridled expansion, these concepts can still be overlaid to Sant'Elia's imagery due to its inherent respect for highly integrated networks that utilize density to deliver reflexive benefit.

In a side-by-side comparison with the work of Ambasz, these images seem barren, almost cold as they exist without any indication of life, but rather document the system of the city itself. One would not look at such a depiction and think of sustainability, but designing a city around its inherent strengths could ultimately yield a more environmentally responsible outcome than focusing first on gardened thoroughfares. Furthermore, there is no reason why Ambasz's plants could not be sketched into such a model. A planted city with weak connections will underperform an efficiently coordinated cityscape that is lacking planted surfaces.

A sustainable urban model will address not only procuring resources for use, but how the resource is used and then how to dispose of what has been used. In many cases, some of the best practices and technologies to accomplish this do not involve plants. Perhaps one of the best modern, built examples of this mantra is the city of Kalunborg, Denmark that has tapped a number of local industries to redirect waste streams into opportunities to serve as feedstocks in different uses. Despite the fact that some of these industries are not the epitome of sustainability (such as oil) the city and its businesses have worked to utilize every bit of energy they can—energy that most of us are simply casting aside.

There are countless examples for areas to target in redefining how we outfit American cities. When I see a proposal for a green urban space I immediately look for the answers to a few questions:

• What density is the city trying to achieve and how is it making inviting, interactive spaces within a dense environment?
• How does the city produce and transmit its power, both on the urban scale or the building scale?
• How is the city using a transportation network to grant people mobility without relying on solely on car traffic? Are its bus, subway/streetcar and bike networks developed, up to date and useful?
• How is the city disposing of (reducing) its solid waste? How does it deal with trash? How much does it reclaim?
• How is the city handling (reducing) stormwater and sewage?

If the answers are repeatedly, "similar to how we do it now," then how much greener can the city really be?

How to Refine the Imagery

The reason why so many have resorted to using plant-based imagery for sustainable urban plans could be the difficulty in representing the truth. Like solar panels and wind turbines, plants have developed a level of recognition in the populace as icons of environmental stewardship. The resulting downside is that many systems (sometimes those that can make the largest impact) are not things that are hung on the outside of a structure but integrated into the building. Examples of this are numerous. Things like Low-V.O.C. paint, formaldehyde-free adhesives, cogeneration facilities, rainwater capture, greywater filtration and cotton insulation are all items that are extremely green but never make an appearance to passing gazes.

Buildings like One Bryant Park or the Cambridge Public Library are both prime examples of progressive projects with hallmark efforts to cast a greener shadow, but neither tip their hat to popular ideas of a green image. While the enthusiast may note that the fading frit pattern on the windows of OBP was designed to regulate heat gain and natural light, the truly impressive systems like ice-storage cooling, greywater filtration and the onsite 4.6 MW natural-gas fired cogeneration plant are all hidden deep within the building's innards. There are only a few that would probably recognize the horizontal louvers in the library's double-skin wall as an extremely efficient construction system.

The answer could include more diagram-based info-graphics that help peel back the skin of projects to identify important components. After enough time, more people could begin to know what to look for when they walk down the street. At a minimum, images of new urban spaces dripping with green should be accompanied by caveats that convey the true breadth of where such goals sit in the continuum of sustainable efforts.