A lofty garden in Libertyville

The soil mixture is much more workable than the clay that permeates many back yard gardens, but this rooftop experiment is a special breed.

A crew of four was back Tuesday morning at the new Lake County permit facility in Libertyville, finishing the task of filling 8,000 square feet with flowers, grasses and ground cover.

One by one, more than 1,500 drought and wind-resistant plants were plopped into 8 inches of special soil atop the roof on the northern portion of the building.

"It's pretty cool, I think," said Patty Werner, planning supervisor for the Lake County Stormwater Management Commission, one of three county departments that moved into the $19 million facility last month.

The mixture includes 15 or 20 varieties of plants but many are of the sedum family, succulent flowering plants that hold moisture in their leaves.

Once the plants are established, the intention is not to water them, Werner said. While employees can view the garden from an adjoining cafeteria or walk onto the roof, the garden is meant to be more functional than aesthetic.

Along with rain gardens and bioswales, the green roof is part of a system of measures to filter pollutants and curb runoff into streams and rivers. Runoff can erode the banks of streams and rivers, and also contribute to pollution by carrying substances such as road salt, Werner added.

"Green roofs can reduce the runoff from the roof surface from 50 (percent) to 60 percent," she said.

Building modifications and other elements associated with the roof garden were funded with a $150,000 grant from the U.S. Environmental Protection Agency. The county also contributed a $67,500 match as a condition of the grant.

According to the Chicago Botanic Garden, roof gardens also can: cool a building in summer and keep it warmer in winter; increase the roof's life span by shielding it from weather extremes; remove carbon dioxide from the air; absorb sound; and, create a habitat for insects and birds.

The Botanic Garden last summer planted 16,000 square feet of roof top gardens as a living laboratory to determine which plants are best suited to grow in that extreme environment - what is described as the most comprehensive rooftop plant evaluation program in the country.

The roof garden is open to the public on weekdays and includes interpretive materials explaining how to create one at home.

Chicago has become noted for rooftop gardens, but they are not common in Lake County. Abbott Laboratories and the College of Lake County are other rooftop garden locations, according to Werner.

"They're just starting to become more popular up here," she said.