Amy Giaquinta's tomato fest has become one of Napa's most popular harvest parties. Her friends come to sample amazing dishes and place orders for seedlings.

When the tomatoes on Amy Giaquinta's 65 plants begin to ripen every summer, she faces a dilemma familiar to gardeners: too much of a good thing. But Amy and her husband, Jerry, have figured out the perfect solution. They invite their friends and Napa Valley neighbors over for an unconventional garden party.

The tomato bash that the Giaquintas host every August allows them to make a minor dent in their multicolored crop of organic heirloom tomatoes with names like Moonglow and Aunt Ruby's German Green. Many of the people they invite are customers who plan to buy seedlings (called "tomato starts") in the spring for their gardens. The party gives them a chance to check out the goods.

"I would never have guessed that Amy would gravitate to gardening," says Jerry, a former Hollywood film executive and now a marketing consultant. A lifelong urbanite, Amy had been involved in media too, working in television production about 10 years ago. When the couple bought their two-acre Napa estate in 2002, it desperately needed tending. "The weeds were bigger than I was," recalls Amy, who worked with an artist friend to turn the former horse pasture into a landscape of vegetables, fruit trees and flowers.

Amy learned how to garden mainly through trial and error, but her talents quickly became evident. Her friends loved the tomatoes she was growing and urged her to plant more. Today she has an informal business, supplying seedlings and tomatoes to friends and local chefs with kitchen gardens—including the chefs at Press and at Gordon's Cafe and Wine Bar—as well as the Dean & DeLuca store. Her neighbor Peter Jacobsen now plants some of her seedlings, and sells some of the tomatoes he grows to the nearby French Laundry.

On an outdoor table shaded by mulberry trees, Amy, wearing a silk dress the color of tomato stems, sets out slices of the 33 tomato varieties she has grown this year. Wineglasses in hand, guests sniff and sample each tomato, then rate it on an evaluation sheet.

For Christy Palmisano, the party is a preview of her own impending deluge. "I have 16 plants," says Palmisano, a muralist. "I thought I'd buy six or eight, but Amy said, 'Oh, no, you need at least 15.'"

The guests, many of them vintners or winery owners, sound like Midwestern corn farmers as they swap tips on ways to irrigate their tomato plants. "Are yours on drip?" one elegantly dressed woman asks another.

Amy and her sons—Jeremy, 11, and Jason, seven—harvest all the tomatoes for the party and make the golden tomato juice for the family's signature Blondie Marys. But to free herself up for her guests, Amy turns the menu over to Joe Vitale, executive chef of Napa-based Melissa Teaff Catering. Vitale's hors d'oeuvres make brilliant use of Amy's tomatoes. He turns hefty Yellow Brandywines into sun-colored gazpacho shooters spiked with jalapeño, garlic and apple cider vinegar. With Amy's prized red-orange tomatoes—the petite, juicy Flammés—and the meaty, jumbo Iowa heirloom Amana Oranges, he creates a gingery, peppery jam to serve with grilled wild-salmon skewers. He places slices of tart Green Zebras over crusty corn-bread rounds slathered with creamy ricotta.

Amy admits to her winemaker friends that her growing methods are less scientific than theirs. If a tomato performs well, she replants it. If it doesn't, it gets the boot. Each winter, she starts between 500 and 1,000 heirloom seeds in Jacobsen's greenhouse, recruiting Jeremy and Jason to help. Once the seedlings are up, they patrol the greenhouse every night with a flashlight, looking for slugs and snails. By May, the seedlings are ready for clients to pick up. "I don't make much money," Amy says. "By the time I figure in my labor, I'm in the hole."

But the pleasure she gets from gardening can't be quantified. Sometimes chefs from the French Laundry come over to graze among her fruit trees after picking up produce from her neighbor. Occasionally French Laundry chef-owner Thomas Keller drops by to view her progress or offer advice on how to improve her plum jam. Chances are good he'll leave with a complimentary basket of peaches or Amy's fraises des bois strawberries.

The tomato harvest doesn't end with the party. For weeks afterward, Amy will put up quart jars of red, green and yellow tomato sauces to line the shelves in her pantry. And using her homegrown basil, she'll freeze endless batches of pesto, trading some of it to Paradigm Winery owner Ren Harris in exchange for his sought-after bottles. It's no wonder that the Giaquintas often have this sign on their front door to reveal their whereabouts: OUT IN THE GARDEN.

Janet Fletcher is a staff food writer for the San Francisco Chronicle and the author or co-author of 18 cookbooks, including The Cheese Course and Fresh from the Farmers' Market.