However, these plants aren't grown for the absent-minded gardener. They're for the burgeoning market for green roofs, where plants help keep out the summer heat and winter cold while also managing storm water runoff and absorbing carbon dioxide.
Plants selected for that job have to be what some might call bachelor tolerant.
Roofs are brutal environments for plants as anyone who has tried to grow tomatoes on their deck can attest. Plants that can thrive in such conditions must be able to withstand high and low temperatures, lack of water and poor soil.
The market for green roof plants is like the plants themselves, small and growing.
Chicago put a green roof on its City Hall in 2000 and since then about 150 public and private buildings have followed, including a downtown McDonald's restaurant and an Apple computer store. The construction of green roofs has been spurred in part by the city's green building and green roof policies, which apply to new public buildings, and private developments and structures that are subsidized by the city.
In addition to requirements that a certain percentage of roof space be constructed as green roofs, the city is also awarding 20 $5,000 grants to help the owners of small commercial properties and residential buildings install green roofs.
"For a city, it really helps to solve a number of our problems," said Sadhu Johnston, commissioner of Chicago's Department of Environment.
"We're finding its brings temperatures down on a roof from 160 to about 80 degrees in the summer."
That can help fight sweltering downtown temperatures that claim the lives of the elderly and sick each summer, he said.
Chicago installed its City Hall roof after Mayor Richard Daley visited Europe, where a mature green roof industry already exists. Now, the City Hall roof also has two beehives from which honey is collected for sale at auction each year, said Larry Merritt, a spokesman for the Chicago department of the environment, whose office looks down on the building.
"From my window here were on the 25th floor you look out during the summer or fall and you see this beautiful garden as opposed to your run-of-the-mill black tar roof," Merritt said.
Chicago is not alone in its zeal for living and working under a living, breathing roof.
In San Francisco, dozens of plants were tested for a 2.5-acre green roof planned for the new California Academy of Sciences building, which is to be completed in late 2008. And at Ford's Rouge Dearborn Truck Plant in Dearborn, Michigan, 10-acres of green roof have been installed.
While many tout the environmental benefits, such as helping reduce the so-called urban heat island effect that can make downtown areas hotter than the surrounding suburbs, proponents say they also have practical advantages. Green roofs extend the life of roofs because they protect the roof from weather extremes.
While each installation is different, studies have found green roofs can cut summer cooling needs and winter heat losses by about 25 percent, according to Green Roofs for Healthy Cities North America, a not-for-profit industry association.