Produce grower Jim Knill spent a recent morning picking lettuce in the greenhouse at his family's Carroll County farm. The job could have been backbreaking labor for the nearly 6-foot-tall farmer.

But this is no ordinary greenhouse.

Instead of stooping over low-lying tables filled with flats of plants, Knill stood tall and reached straight out to pluck the leaves from plants growing in high tiers of aluminum rain gutters.

Like most greenhouses, this one allows Knill and his family to extend the typical growing season of a number of fruits and vegetables, making them available 10 months out of the year. But it also allows them to test, in cooperation with the University of Maryland, an innovative design that maximizes indoor growing space and reduces the strain of greenhouse labor.

Only two greenhouses with this "high-density" design are in use in the region, and the one operated at the Knills' 182-acre farm in Mount Airy is apparently the only one producing fruits and vegetables for market.

The greenhouse, owned by the state but built on a hill overlooking the Knills' farmhouse, contains four areas of plantings that run its 100-foot length. Each area holds eight rows of aluminum rain gutters, staggered like a staircase on tall wooden platforms, four gutters to a side.

The high-density system provides an ergonomically correct "comfort zone" between a person's waist and chest. The zone's height can be adjusted, even set to meet the needs of someone in a wheelchair, said Bryan Butler, an educator in the University of Maryland Cooperative Extension Service's Carroll County office.

Because the Knills run a well-established farmers' market, Butler asked them to participate in the experimental project.

Under a university grant, Butler is evaluating every aspect of the system, from how cost-effective it is to the quality of the crops produced.

Butler said he was intrigued by the economic potential the high-density greenhouse appears to offer for some produce sellers. "People on small acreages or with direct marketing opportunities [can] take advantage of the high prices at the beginning and the end of the season," he said.

Local strawberries ripening early in the season or long after the typical strawberry season has passed tend to command a higher price, Butler said.

Because the Knills sell produce to a local restaurateur, they have a ready outlet for the greenhouse crops - which is key to the greenhouse's success, Butler said.

The University of Maryland gave Butler an $8,900 grant to help build the greenhouse. David Lankford, an Eastern Shore nurseryman who designed the high-density system, erected the tiers of gutters for free - an "in-kind" contribution worth about $9,000, Butler said. The Knills paid additional construction costs and have contributed countless hours managing the greenhouse - under Butler's supervision - since it was built in February.

The rows in the Knills' greenhouse are filled with radishes, squash, strawberries, mesclun and other varieties of lettuce. Plants such as cucumbers grow in the bottom rows so that their runners have room to spread, Knill said. He also has raspberry bushes growing in large pots around the unused space at the outer edges of the greenhouse.

Managing such a variety of plants in a relatively small environment has been challenging, Knill and Butler said.

So far, though, the cost of the aluminum gutters - about $9,000 - appears to be the biggest problem with the design. That cost can double the price of a typical greenhouse, Butler said.

Lankford pointed out that the gutters are expected to last about 20 years. He said he expects it will take only two years to recover their cost, though Butler's research has not confirmed this estimate.

Hardware aside, the real bottom line in a greenhouse is the quality of the produce.

The Knills were selling their fruits and vegetables to Todd Bricken, who owns the Brick Ridge restaurant a few miles down Route 27, when they added the high-density greenhouse to their operation. It has allowed them to offer Bricken a variety of produce outside the local growing season.

Bricken said he usually stops by the greenhouse once a week to check the crops and chat. He said buying from the Knills affords him a relationship he could never get at one of the large wholesale markets.

Wandering past rows of mesclun seedlings, Bricken said that when he complained the plants had gotten "too stemmy" for salad, Knill planted seeds farther apart to fix the problem. And when he said he might be able to use more strawberries, Knill planted more.

Eating a freshly picked radish, Bricken said, "I just can't beat the quality."