How green is my grass!

Mary E Myers, a landscape architect and associate professor at Temple University, had more than absorbing stormwater in mind when she created a 200-sq-ft rain garden beside her sloping lawn in a suburb north of downtown Philadelphia.

“I wanted to increase biodiversity, but I wanted it to be aesthetically appealing, so that people would accept it and want to do it,” said Mary, 62, standing by the sweep of blue mistflowers rolling down to the sidewalk.

She often gives people some seeds or self-seeded native plants. And when someone from down the street longs for those blue mistflowers, she says, “Don’t worry, the wind will bring them to you.”

With the shapes, colours and textures of more than 50 native species here, the elegant branching of the young black gum tree, the dogwood and shadbush turning deep red, the handsome seed heads of hibiscus, the fig-like fruits of the bottlebrush buckeye - this dynamic landscape is nothing like the scruffy patches of weeds too often referred to as rain gardens.

When Mary and her husband, Daryl Carrington, an architect who teaches
sustainable design at Temple, moved here in 2005 with their two college-age sons, they had mixed feelings about the neighbourhood. They liked the diversity of architectural styles, dating from the 1930s, and the walkable streets shaded by native beech, oak, hickory and tulip trees.

“I really appreciate the feeling of being lost in these trees,” Mary said one afternoon a couple of weeks ago, gesturing toward the beech trees that tower over their two-story stone house. “They’re part of a shared grove, which is very nice.” But their oddly shaped lot was only a third of an acre, with no backyard and a north-facing front lawn with a 12-foot drop to the sidewalk. And they were right on the corner. “I lamented for a long time how exposed we were to the public,” she said. “But there’s a really interesting social
aspect to all this.”

Learning from education

Mary, who earned her master’s degree at the Harvard University Graduate School of Design, is the former chair of Temple University’s department of landscape
architecture and horticulture, where she helped create a master’s programme in
landscape architecture focusing on ecological restoration.

As an undergraduate at the University of Wisconsin, she studied with Darrel Morrison, who took his students into the prairie to study the principles of
restorative landscapes. And her mother was an ecologist, who led her five children through the forests and swamps of Pennsylvania, Maryland and the lake country of Wisconsin.

But here she was, living in a neighbourhood of manicured lawns. It slowly dawned on her that this corner lot was a teaching opportunity.The first few years, she contented herself with pulling out the exotic plants: the European privet and false cypress against the side of the house, the clipped yews and Chinese forsythia, the Japanese azaleas.

She counted 23 species when they moved in, 16 of them non-native. Now the count is up to 127, most of them native. It wasn’t until the late spring of 2012 that she began work on the rain garden, which stretches 60 feet along the base of a retaining wall at the foot of the yard. “We dug it out with a backhoe, but you could use shovels,” said Mary, who laid out the biomorphic shapes with her garden hoses. “We did it in a day.”

She added two dry wells, basically holes three feet deep filled with gravel. The dry wells hold water during heavy storms and slowly disperse it into the ground. The soil itself has not been amended, except for a little compost mixed in the clay. She based her choice of native species on a plant community approach, meaning she used the same combination of plants that grow in a nearby wetland.

To attract native insects and animals, as well as her neighbours, Mary chose herbaceous native species with showy summer blooms, like goldenrod, verbena, milkweed, cardinal flower, mistflower and hibiscus. And she added woody plants like flowering dogwood, witch hazel, spicebush, winter berry, swamp rose and buttonbush, along with trees like redbud and black gum, to create a diverse, dynamic habitat that could absorb and
filter water and put on an ever-changing show for the neighbourhood.

“This is where the pipe from that side of the roof comes out,” Mary said, pointing to the mouth of a white plastic pipe nestled between a few heavy rocks. “The stones are deflecting the force of the water, but look at that verbena right by the pipe. It’s as happy as can be.” The 5-foot flower stalk had been loaded with bluish-purple
flowers a month ago. Now this Verbena hastata, or blue vervain, leaned against my shoulder, dangling long tassels of seeds that the juncos love to eat. Its leaves had a few bites here and there, where the caterpillars of the verbena moth must have been feeding; buckeye butterflies lay their eggs here, too, and bees and wasps sip nectar from the flowers.

CamouflageShe didn’t paint the pipes to blend in with the foliage, she said, because she wants people to see them and ask, “What are those for?” Then she can explain how the system works: The pipes are angled underground from the corners of the house, 25 feet away, where they connect to the downspout. So stormwater drains into the garden, rather than the street and the storm drains that would have directed it to Tookany Creek, a quarter-mile down the hill.

“We’re holding the roof runoff from the Tookany,” Mary said, “which is a highly eroded, very polluted stream that feeds to the Delaware River.” Like many old cities, Philadelphia has a combined sewer system, which means stormwater flows into sewer pipes and out to the nearest creek or river.

“Because of this enormous volume and velocity of water that we’re sending downstream to Philadelphia,” she added, “in a way we’re responsible for the sewer outfall.” So the more suburban homes that hold back their stormwater with rain gardens, the less polluted water will reach rivers and bays. Philadelphia is one of the first cities in the country to use this kind of green infrastructure, which harnesses biological systems to buffer storms, clean water and prevent erosion, rather than the more expensive proposition of replacing decaying pipes and culverts.

Recently, a few of Mary’s neighbours have begun asking for help designing their own rain gardens. “But I don’t think it’s a good idea to work for your neighbours,” she said. “I’m always happy to give them seeds and information. But when they want to hire me, I refer them to my students.”