What are they smoking at Southern Co.? Grass.

The Atlanta-based parent of Georgia Power is mixing grass pellets with the coal it burns at Plant Mitchell in Albany. The green stuff -- coastal Bermuda, switchgrass and, on the horizon, fescue -- reduces emissions at power plants.

Southern could use the clippings. The company is Georgia's single biggest air polluter. Federal environmental regulators are suing over aging coal-burning plants. And shareholders recently tried to pass a resolution pushing Southern to clean up its act.

The company has been testing switchgrass at an Alabama plant since 2001. In April it extended testing to Plant Mitchell in South Georgia, this time compressing the grass into little cubes to work through the system better.

"The goal is to find cost-effective means of using renewable energy," says Doug Boylan, a company research engineer.

Grass is more expensive than coal, though the company declines to estimate how much more it costs.

Don't bother volunteering loaded lawn mower bags. The company has lined up grass farmers in Georgia and Alabama.

Grass at the Alabama plant cut coal use up to 10 percent, with a similar reduction in sulfur dioxide and mercury emissions, Southern says. Now the company plans to charge a premium to Alabama customers who volunteer to use environmentally friendly grass-fueled energy.

But grass won't significantly replace coal, says Charles Goodman, Southern's senior vice president of research and environmental affairs.

"It is land-intensive. You have to grow a lot of grass in order to generate a megawatt," he said.

The company's grass consumption deserves praise, says Stephen Smith, executive director of the Southern Alliance for Clean Energy. But he considers it "a minuscule" effort for such a big company. "We think they can be providing significantly more leadership."