OELWEIN -- A spendy experiment is paying off for a greenhouse, sprouting revenue for a 36-year-old business.

Oelwein Landscaping started growing lettuce last winter in one of its greenhouses using a method called hydroponic gardening.

The process uses no soil whatsoever. Instead, the indoor technique involves an elaborate system of pipes and tubing that circulates water and nutrients to plants.

The method is centuries old but has gained popularity in the past decade for some of the same reasons the organic market has grown: Consumers see hydroponics as a healthier, environmentally friendly alternative and are willing to pay a premium.

Owner Dieter Erdelt, 66, decided to branch into the budding hydroponic business last fall. When he started his gardening shop in 1968, there was little competition in the area, he said. But now every neighboring town has its own nursery.

The closest hydroponic lettuce grower he knows of, however, is across the state near Sioux City. So in December Erdelt invested $60,000 installing a hydroponic system.

Today that section is twice as productive as any other part of the greenhouse, accounting for about a quarter of all revenue.

"It really worked out better than I expected," Erdelt said.

Since he harvested his first batch, he's sold every head of lettuce. Hy-Vee was among the first to jump on board, buying up hundreds for its Waterloo and Cedar Falls grocery stores.

"People want it," said Jeff Thill, produce manager at the Crossroads Hy-Vee store. "It's really crisp and tender. There's a lot more water in it compared to the stuff we get from California."

The lettuce is packaged in a plastic tray with instructions to rinse the head after purchasing. Because a nub of roots is still attached, the plant will continue drawing water for several days.

Even though the hydroponic lettuce costs about twice what a typical head of iceberg lettuce goes for, the Crossroads Hy-Vee sold its first batch of 100 within three days.

Besides price, supply is another drawback, Thill said. The product was out-of-stock last week at Hy-Vee. Thill expects more this week.

At the greenhouse, Erdelt plants 800 heads per week. The first step is pushing each seed into a small block of rockwool, a soft, porous material derived from limestone.

Once the roots take hold, the tiny cubes are transplanted into square openings on a set of long, white plastic beams that run up and down both sides of the room. Each holds about 15 sprouts spaced 8 inches apart.

The white platforms are connected by a circulatory system of PVC piping and tiny black tubes that feeds water and fertilizer blended by a machine at one end of the room.

From seed to harvest, the process takes about two months. Because it's done indoors, Erdelt can control more variables than field farmers can. There is no need for pesticides. He doesn't have to worry about soil-borne diseases, and when he harvests, his lettuce heads are free of dust and debris.

Robert LaGasse, executive director of the Hydroponic Merchants Association in Manassas, Va., said the hydroponic industry has benefited in the last decade from growing public concern over environmental and food safety issues.

"In the 1950s, no one worried about pesticides and overfertilzation Today they do," he said.

The method is ideal in locations where conditions are hostile for outdoor farming, he said. It allows local producers to grow things that otherwise would have to be trucked in from far distances.

Erdelt is not the only grower in the Cedar Valley having success with hydroponic growing. Mark Hommez has successfully grown hydroponic tomatoes in St. Ansgar for close to a decade.

Cost is still a barrier for some consumers, but as technology improves and operations get larger and more efficient, the price gap is gradually shrinking, LaGasse said.

For now, though, Erdelt's customers don't mind paying extra. The Oelwein greenhouse is operating at maximum capacity and couldn't take on any new customers without expanding.

"It's just so fresh," Luigi's Restaurant manager Marty Staci said. "It keeps much better. It doesn't turn brown the way a lot of your lettuce from wholesalers does."

The 45-year-old family-owned restaurant uses the lettuce in its salad bar and sandwiches.

Erdelt plans to experiment with other vegetables and varieties this year to find the best crops for his customers. He also hasn't ruled out expanding the hydroponic system to other parts of the greenhouse.

"I didn't expect it to move that fast," he said.