The patient arrived at the lab looking seriously ill, with lumpy green tumors. A family member had decided to get professional help to answer a serious question: Does the patient have cancer? Hours later, the opinion came down. The tumors were benign. The patient would survive.

This was no day at the oncologist's office. The lab was the Fairfax County Master Gardeners Association's diagnostic center. The family member was Patricia Fausser of Springfield, whose sick patient was a branch from the star magnolia tree in her front yard. And the doctor? Expert horticulturist Adria Bordas.

Bordas supervises the county's 220 master gardeners, who spend the warm-weather months helping Fairfax residents with questions about their lawns, gardens, trees and shrubs. In a county acutely conscious of property values, yard upkeep is important to many homeowners, so the master gardeners stay busy.

People bring dozens of plant samples each week to clinics at farmers markets, libraries and fairs, where the expert horticulturists greet residents and answer their what's-wrong-with-my-garden questions. Unusual cases are referred to a laboratory inside the Merrifield Garden Center on Lee Highway in Fairfax, where members of an elite group of master gardeners peer into microscopes and diagnose diseases and insect and animal damage. Fausser initially brought the star magnolia to the Burke Farmers Market, and from there the sample was transferred to the diagnostic lab.

The service, which often involves painstaking investigative work, is free. The master gardeners do not draw a salary for their calling. They do it out of a fascination for all things green, said Bill Anderson, acting president of the Master Gardeners Association.

"It's the camaraderie between the master gardeners and the fact that we are able to help the citizenry of Fairfax County with their problems that makes it so special," Anderson said. "You can spend a lifetime learning this stuff. We really get excited when something comes in that's unusual."

The program was launched 29 years ago by Virginia Cooperative Extension, a partnership between the federal, state and county governments. Back then, one of the main goals of the extension service was helping farmers with agricultural problems. But as the county grew, so did the demands of Fairfax homeowners. These days, the program is not about helping farmers grow crops. Instead, the focus is on maintaining the health and appearance of yards and gardens in the county's suburban neighborhoods.

Being a master gardener is a badge of honor, Anderson said. It takes a candidate 75 hours of community service and 90 hours of training over three years to earn the title.

"It's so enjoyable to pass on what you learn," said Becky Barker, 52, a master gardener for nine years. "When they find out [what I am], people at work and my neighbors are always coming up to me with seasonal questions."

Occasionally, a resident will bring the master gardeners something exotic.

In 2002, a woman discovered a fuzzy, wide-winged insect that looked like a bee but was snacking on her Japanese euonymus shrub. None of the master gardeners could identify it. Even experts from the Smithsonian Institution were scratching their heads.

Then a professor at Virginia Tech identified it as a Pryeria sinica, a moth native to Siberia, as well as China and other East Asian countries. Somehow at least one of the moths had hopped aboard a plane or a boat and ended up in Fairfax County. Now, the pest is making a home in the Washington area.

"The first time it was spotted in North America, it was found in Fairfax County, so that was pretty cool," said Bordas, who coordinates the Virginia extension service's horticulture activities in Fairfax, including the master gardener program.

Patricia Fausser's star magnolia is the jewel of her front yard, she said. The slow-growing tree, a native of Japan, has large white or pink flowers in spring before the leaves appear. But this year Fausser said she noticed green tumors hanging off the branches.

"I'm hoping it's not anything that kills the tree. It's a very beautiful specimen," said Fausser, 45. "It's got white flower petals and a beautiful fragrance. I get a lot of compliments."

After the initial examination at the Burke Farmers Market, a branch of the tree was transported to the lab at the Merrifield Garden Center. Bordas and several other women were there, working quietly around a large table cluttered with plant samples, notebooks, pencils, reference books -- and a plate of low-fat brownies. Two microscopes lay near a window sill.

The women labored at their passion from morning until late in the afternoon. They are among the county's best master gardeners. Barker, one of the youngest, said she was required to finish years of community service and pass several interviews before she was allowed to work in the lab.

The most experienced was Edith Probus, 79, a master gardener for 26 years. Probus's colleagues say she has an encyclopedic memory and a knack for recognizing odd insects and plants.

"We learn something new every time we go to the plant clinic," Probus said. "I also enjoy the ladies' company. I'm always looking forward to coming and finding something new and to be with all my friends here."

Jane Meyer, 83, examined the star magnolia. Cutting it with a scalpel, she slid small samples underneath a microscope. The tree's inner parts looked healthy and intact. The cause of the tumors remained a mystery. Perhaps a bug had tried to lay eggs in the tree's branches and caused the deformity, she speculated.

But she was confident the tumors were benign. Fausser was relieved.

The women at the lab said some people become master gardeners and use the title to promote their own nursery businesses and flower shops. But that's not what the program is about.

"We are looking for someone to be in the program for a long time. We don't want people who are in the program who just leave," said Bordas. "We are looking for someone who has the time to volunteer and the spirit of volunteerism."

Master gardener Jane Meyer identifies a sample of ragweed. She and other volunteers do their work above the Merrifield Garden Center on Lee Highway in Fairfax. Adria Bordas, who coordinates the master gardener program in Fairfax, inspects a branch from a red maple brought to the Burke Farmers Market by local resident Susan Stahler. During the growing season, master gardeners hold weekly plant clinics throughout the county.Lynn James, left, talks with Aaron Fausser of Springfield about a star magnolia branch with tumors from a tree in the Faussers' front yard.James inspects a star magnolia tumor before transferring the sample to the diagnostic lab. At the diagnostic lab at the Merrifield Garden Center in Fairfax, master gardeners Jane Meyer, left, Marie Olson and Becky Barker consult reference materials.