Go to the nearest container-grown plant, stick your finger in the dirt and ask, "What's in there?"

Nobody knows. At least, not exactly.

Most likely it's some mixture of soilless growing media -- dirtless dirt. A combination of organic matter and something inorganic like sand or perlite, it's what most container plants are grown in now.

Growers like soilless mixes because they're lightweight and drain well.

"Soil can be highly variable in content and pH, and can contain undesirable pathogens or nematodes," said UGA professor Franklin Pokorny. "Generally, soilless mixes don't have these problems."

For years the standard mixes were largely peat moss and sand. In 1960, though, Pokorny began investigating using pine bark, a waste product at the time, to replace peat.

Pine bark has since become a standard and Pokorny the top authority in a field that, after decades of study, he can still say is in its infancy.

That doesn't mean the research hasn't come a long way.

And the work is gaining a new tool to speed the process: UGA researcher Silvia Bures's work is taking the guesswork out of potting mixes.

Combining physics and horticulture, Bures used computers to simulate what happens when soilless media particles are mixed. She and colleagues Alan Ferrenberg and David Landau designed a program that ultimately will allow manufacturers to create the ideal mix for any need.

The possibilities are endless.

"Every day some industry has waste they want to convert into profitable material," Pokorny said.

The problem is: Endless materials and particle sizes make the exact nature of soilless mixtures a mystery even to the people who make them.

"When this technology is far enough along," Pokorny said. "it should help manufacturers and nurseries that make their own mixes know what's in them. It will provide consumers a known, uniform product, presumably at lower prices."

The research, though, seems as endless as the possibilities.

"We're the only ones working along these lines, trying to model container media," Pokorny said. "It opens a tremendous area for study."

It's a risk scientists run in any new area. The work is slow because you can't leapfrog ahead on other people's research. How fast your work develops depends on the support it gains.

So designer dirt may yet be a long way off.

"I'd hate to try to predict when it will have practical usage, but if I had to hazard a guess," Pokorny said, "I'd say we're a decade away. But you never know. Things happen."

Things happen, indeed.

In 1992, Georgia growers thought an epidemic of black thumb was going around when large-greenhouse owners and homeowners alike had plants turning yellow and dying.

"Nurserymen had trees die within weeks of transplanting," said UGA extension horticulturist Paul Thomas. "Poinsettia and pansy growers' plants looked terrible."

Thomas and Larry Windham, president of the Georgia Commercial Flower Growers Association, studied the mysterious malady and found the dirty culprit: soilless mixes with too much fertilizer and a high pH.

Without an ingredients list to check, "the growers inadvertently made matters worse by adding more fertilizer," Thomas said.

When people realized the problem had cost them more than half a million dollars, support grew quickly for some landmark legislation.

As a result of Thomas's studies and the groundswell of support for change, the Georgia General Assembly passed the Georgia Horticultural Growing Media Act of 1993.

The law, which took effect July 1, 1994, requires soilless media manufacturers to register their products with the state Department of Agriculture.

Now, consumers can know pH and type of fertilizer in a media mix and what plants will grow in it. "For the first time, we have soil information to manage plant growth," Thomas said.

Both Thomas and Pokorny said they expect the law to be quickly duplicated in other states.

Suddenly, manufacturers everywhere may be pondering pots and wondering what, precisely, to put in there to provide the most reliable soilless mixes for whatever growers grow.

Momentum may be gathering.