FLORENCE, S.C. (AP) — If agave, yucca and asparagus plants slowly waking up from winter atop the facilities building at the Moore Farms Botanical Gardens building in Lake City had faces — you know, like those pansies and roses in "Alice in Wonderland" — they'd doubtless be full of surprise and wonder.

Which would make them a perfect match for looks they receive from the people down below.

Plants on the roof? A gable garden? What the heck is going on?

The 6,000-square foot green roof at the Moore facility, the garden center built by Lake City philanthropist Darla Moore last January. It is one of a handful of new "green roofs" that are springing up in the Pee Dee. They are part of a national experiment in green building design. The roofs can save money and help mitigate environmental impact by cutting down on energy use and mitigating storm water runoff.

The J.L. McMillan Federal Building in Florence and the McNair Science Building at Francis Marion University are also experimenting with green roofs.

Green or living roofs have gained popularity in New York, Chicago, the Pacific Northwest and in Europe. The Pee Dee-area experiments are designed to figure just which plant varieties will work best around here.

"What we're trying to do is find out what varieties work best in South Carolina's climate," said Ethan Kauffman, garden director at Moore Farms, said. "So we've come up with a palette of plants that we think would work for the roof and the hot and humid conditions of summer. Right away something's failed (that is, the plant has died), but failure is success in this situation because it tells us what's working and what's not."

The building was designed to handle the heavier rooftop load: approximately 6 inches of soil contained in cells that prevent the soil from running down the pitched roof in heavy rains. The pitch is important, though, because it allows water to flow through the soil onto a mat that sits above the roof membrane and the concrete and steel roofing material. The water then runs into a gutter, taking it to a 12,000-gallon cistern - essentially a giant rain barrel - that irrigates the garden when rain clouds aren't around.

"This keeps the water and UV light off the surface and doubles the life of the roof compared to traditional roofs," Kauffman said. "And when it rains, it takes three hours for the rain to migrate off the roof from bone dry conditions."

Those advantages, plus the potential savings in energy costs and meeting new sustainability standards led to a 28,500-square foot green roof atop the federal building in Florence a little more than a year ago. Living Roof from Asheville, N.C., won the bid to build the green roof system. The roof system is designed to meet new government principles to incorporate sustainable design and energy efficiency as seamlessly as possible into all building projects. The project involved 329 tons of growing medium and was part of a larger roof replacement project that cost $2 million.

Francis Marion University also joined in the fray, erecting a living roof on a 3,000-square foot section of the McNair Science Building. It is just one of the many public and private institutions across the world evaluating potential savings.

Unlike the custom green roof in Lake City and on the federal building, the array atop the McNair Science Building is made up of modules from Michael Whitfield's Charleston-based Green Roof Outfitters. The modules have a built-in drainage layer, filter fabric and lightweight growing media that helps lighten the load and retain moisture. They also provide significant cooling. Not many things get hotter than a Pee Dee roof in the middle of the summer.

"On an 80-degree day, a black roof can get up to 170 degrees," Whitfield said. "Cool white roofs get to about 125 degrees, but a green roof will stay around 10 degrees of ambient temperature (that is, near 90). While they help with insulation, their real benefit is with heat gain in the summer."

The university obtained a $40,400 grant from the South Carolina State Energy Office in 2011 that covered the project that was completed last October. It includes sensors underneath the modules and in the building to monitor energy levels.

The typical cost of a green roof is about $10 a square foot. Whitfields modules ranging from $11 empty or $44 fully loaded. Once the roof system is set up, there is little maintenance involved. The maintenance may depend upon what's planted.

"Green roofs are low maintenance ... but require some maintenance because they are a living organism," Whitfield said. "If you do have a drought season, you may have to water or set up a system to fill in the dry times or get up with the hose."

In addition to energy savings, the living roofs can establish a new wildlife habitat, produce cleaner air and reduce noise pollution. The water flowing from these living roofs is also cleaner and lessens the load on storm water infrastructure during downpours, according to Terasa Young, natural resources agent for Florence and Darlington Counties and Carolina Clear Coordinator for the Florence/Darlington Stormwater Consortium.

"During large rainfall events, it's not so much capacity of the storm water system as it is to the downstream effects to whatever body the water flows into," Young said. "The extra water and the velocity of that water causes erosion in that water body."

Young says a 1-inch rainstorm on a 1,000 square feet of roof space generates 600 gallons of water. Each of Whitfield's modules captures 1.1 gallons of water per square foot when fully saturated.

While Whitfield's business continues to grow, especially in states and cities that offer tax incentives, he said the trend will not start to really trickle down until more incentives are offered in South Carolina.

"Once they get familiar and comfortable and realize they don't have to mow the roof or that it will take over or cause leaks, it actually prevents leaks, once we get a few more around it will become bigger," Whitfield said. "Once they get a tax incentive that will help. A state or city incentive, that'd really be the driver."