Parking Gardens

Parking lots make great settings for film noirs—I’ll give them that. But they’re bad for the environment. Their extensive paved and impervious surfaces bake in the sun, exacerbating the urban heat island effect. Virtually all the rain that falls on them is funneled into storm sewers, polluting local waterways. And they’re some of the ugliest places on the planet.

Public gardens are leading the way to greener parking lots—parking gardens—with plantings that absorb rain and prevent runoff and solar arrays that produce energy while providing shade.

Here’s my “Growing Greener” column on three of these state-of-the-art parking gardens, which appears in the latest issue of Public Garden,  the flagship publication of the American Public Gardens Association. In my “Growing Greener” columns I answer sustainability-related questions from public garden staff.

Q: What are some things to consider when planning a green parking lot?

A: America’s car culture has given rise to several soul-killing types of architecture, perhaps none as notorious as the parking lot. Typically barren expanses of asphalt, parking lots have become symbols of social disorder, often portrayed in contemporary art and film as settings for crime and violence. The extensive paved and impervious surfaces exacerbate the urban heat island effect, and since virtually all of the rain that falls on them becomes runoff, they are one of the most significant sources of urban water pollution. In short, a conventional parking lot is not the kind of place that makes a good first impression on garden visitors.

Not surprisingly, a growing number of public gardens have been taking a hard look at their parking lots. Just last year, for example, Missouri Botanical Garden announced the completion of sustainable renovations to its east visitor parking lot, while Queens Botanical Garden opened a new, four-acre, green parking garden. In January, the Cincinnati Zoo & Botanical Garden made headlines when it announced visitors would soon be greeted by the largest publicly accessible, urban solar photovoltaic array in the country—a 1.56 megawatt system installed on a canopy structure over its Vine Street parking lot that not only will provide shade for nearly 800 of the 1,000 spots but also generate some 20 percent of the institution’s energy needs.

“From the beginning,” says Susan Lacerte, Executive Director of Queens Botanical Garden, “our main concept was that we wanted our visitors to arrive in a garden.” QBG’s “parking garden,” like Missouri’s “eco-lot,” features bioswales planted with native trees, shrubs, and wildflowers along with various types of porous paving to absorb stormwater runoff. “Stormwater and shading strategies that use plants are a natural fit for public gardens,” says Kara Roggenkamp of MTR Landscape Architects, which designed Missouri Botanical Garden’s renovated parking lot. With beautiful plantings and pavers instead of solid asphalt, a parking lot can offer improved environmental performance while meeting a garden’s high aesthetic standards.

Strategies for absorbing and cleansing stormwater and providing shade for visitor comfort and to help reduce the heat island effect are major considerations, but they aren’t the only ones. Other things gardens looking to green their parking lots should consider are size, materials, and interpretation.

More than one observer has called “green parking lot” a contradiction in terms.  Way up on the list of a parking lot’s environmental impacts is the fact that it invites people to drive. It also takes up valuable space. For these and other reasons, it makes sense for gardens to offer incentives for biking or taking public transit, and to make sure their parking lots are as small as possible. Forward-thinking planners offer not only ample space for parking bikes but also plug-ins for electric vehicles. Among the U.S. EPA’s best management practices for green parking are providing spaces specifically for compact vehicles and minimizing the dimensions of the remaining parking spaces; while large sport utility vehicles are often cited as barriers to downsizing stalls, the agency maintains that most local parking codes require stall widths wider than the widest SUVs. And instead of building for peak parking needs, gardens can look for opportunities to share parking with an office or other organization that doesn’t take full advantage of its parking facilities on evenings or weekends.

Materials, as Roggenkamp points out, are a sustainability issue with any new construction.  She suggests that gardens recycle demolition materials and use recycled and/or locally sourced materials as much as possible. In Missouri Botanical Garden’s renovated parking lot, the asphalt paving includes 15 percent recycled content and sits on a base of crushed recycled concrete.

Light fixtures in Queens’ parking garden are designed to so-called dark sky standards to reduce light pollution that can harm plants and wildlife, and they are powered by photovoltaic panels. Using parking lots to generate substantial amounts of energy, as is being done in Cincinnati, is another way to make the most of formerly unproductive space. Some parking lot experts predict that entire “forests” of “solar trees”—photovoltaic arrays that maximize energy production by tracking the sun like plants—will soon be sprouting in parking lots.

How much does green parking cost? That depends on the circumstances and technologies utilized. QBG estimates its parking garden cost about $11 per square foot.

Public gardens are educational institutions, and green parking lots are great teaching opportunities as well as transportation amenities. The new facilities at Missouri and Queens include interpretive signs that explain the environmental strategies employed, and how visitors can use them at home. Cincinnati Zoo & Botanical Garden’s solar canopy will include an educational kiosk that allows visitors to learn about the array’s performance and the benefits of solar energy in general. Roggenkamp notes that gardens even have an opportunity to help advance best practices by, for example, testing tree-planting techniques such as increased soil volume under pavement.

“Our parking garden is already a teaching garden,” says QBG’s Susan Lacerte. “The public loves it.” “It’s beautiful when it rains,” she says, “and the stormwater management works great.” Her advice to other gardens: “Do it!”

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