Growing for rooftop gardens

1.01.06

By CARYL VELISEK

There’s a quiet, green revolution going on high above city streets that few people are aware of. It’s called greenroof. Ed and Lucie Snodgrass are a fifth generation farming operation and have been growing greenroof plants at their Emory Knoll Farms perennial nursery for five years for wholesale distribution. They have been specializing in greenroof plants and are currently stocking more than 100 varieties. Greenroof is basically the planting of vegetative rooftops, the planting of certain plants on rooftops to capture runoff that would otherwise go into streams and rivers and eventually into water systems such as the Chesapeake Bay.
Greenroof is not a new concept, according to Ed Snodgrass. Europeans have been using it for 30 to 40 years.
Greenroof is actually another way to protect the Chesapeake Bay and its tributaries, he said.
“It’s designed to perform the function to reduce imprints of impervious matter off the tops of buildings.
“In this area, you would have to have been living in a cave not to have heard about the issues involving the Chesapeake Bay. Scientists have been attacking the problem of storm water loading of the bay for years.”
Geographically, almost all cities in the area of the bay are port cities, Snodgrass explained. The suburbs tend to go upward in elevation and water is funneled downward into sewer systems and water treatment plants and into the bay.
“When there is excess rainfall, treatment plants can’t handle all the runoff. Quantity as well as quality of storm water has gotten to be an important issue,” Snodgrass said.
Many cities’ systems are at capacity to begin with, he said. When the sewage system gets overwhelmed by a storm for instance, the system can’t treat all the water flowing in and pipes have to be opened to avoid flooding.
“Greenroof sequesters 60 percent of annual (normal) rainfall and captures it, letting it out slowly. In addition, air pollution can be consumed and cleaned by plants. Pollution works into the plant media and roots can make use of much of it.
“Five years ago, we were looking for a market that was a little more untapped and a little more environmentally friendly when we heard about greenroof. We were a fairly small company so the transition was not difficult,” Snodgrass said.
“We don’t know yet how big it will be or how fast it will grow.
“We couldn’t do this without consulting with roofers, landscape contractors and engineers,” Snodgrass said. “We also have a different clientele like architects and building planners.
“There are two types of greenroofs: Intensive, where you have 6 inches or more of media, sometimes up to 2 to 3 feet thick, designed to hold a great deal of weight; and Extensive, which is more of the world we operate in, with 3 to 4, sometimes up to 6 inches of media.”
Media is 80 to 90 percent inorganic material composed of expanded slates, clays and shales, with the rest in organic matter, and sometimes some perlite. It resembles gravel, Snodgrass said.
“We provide a wide selection of plant material, roof garden experience, and deep plugs for higher survivability and we are happy to custom propagate plants to buyer specifications.”
Greenroof plants are limited at this time, to a wide variety of hardy succulents, which can change from region to region. It would be difficult to expand the plant list, Snodgrass said, without expanding the media and adding irrigation, but there is constant experimentation.
Emory Knoll has plots on site to test plants, soil mixtures and water retention qualities and several sustainable design features have been integrated into the operation.
“We are dedicated to sustainability and to preserving the environment,” Snodgrass said. “And we are a leader in horticultural consulting for greenroof projects.”
Solar power is used to pump all water used in the greenhouse and photovoltaic cells (solar panels) supply most of its electrical needs. They also use diesel fuel made from used French fry oil.
“We’ve shipped plant material all over to places like Singapore and Japan,” Snodgrass said. To date, Emory Knoll Farms has provided a little more than a million square feet, or 23.75 acres, of planted roofs in 163 projects, and, Snodgrass said, that will have reached 200 projects by spring.
“Washington, D.C. has 2,500 greenroofs and Beijing, China, is going to have a lot of them for the next Olympics to show off that they are friendly to the environment. Unless you know the greenroofs are there, you probably wouldn’t see them,” he concluded.
There is one greenroof that may be visited by the public at the Mikulski Center at Caroline and Lancaster streets in Fells Point in Baltimore, Md.
The Web site for Emory Knoll Farms is www.greenroofplants.com and they may be reached at (410) 452-5880.