The goal of the National Heirloom Expo is to change the way people see and grow fruits and vegetables.

Shiny, uniform, smooth and common are out. Old varieties that at one time would have been considered homely and unworthy of a spot in the supermarket produce section are venerated by the thousands of growers, home gardeners and vendors pouring into the Sonoma County Fairgrounds in Santa Rosa this week for the seventh annual harvest event.

They come from throughout the United States and around the world to admire odd squash, have their pictures taken in front of towers of vegetables, buy organic heirloom seeds and other gardening supplies, and listen to talks from more than 100 speakers, including environmental activist Robert F. Kennedy, Jr.

The Kennedy family scion appeared Tuesday night on a panel discussion about the controversial weed killer glyphosate, commercially sold as Roundup and determined to be carcinogenic.

“This is to preserve our vegetable heritage and pass it on to the next generation. If we don’t do it, no one will,” said David Johansen, one of 300 farmers who grow plants to supply to Baker Creek Seed. The Missouri-based seed company is a leader in the global movement to preserve disappearing heritage varieties and the force behind the expo, now in its seventh year.

Nicole Halloran, her husband and two sons came from Knoxville, Tenn., just to attend the expo, hoping to learn more about organic growing from experts in the field as they start their own small produce farm. She said her oldest son Liam, 12, was particularly excited.

“We are just fascinated by pure food and want to learn more about it,” she said. “We are real fans of those who are into preserving our heritage seeds. My husband is still working but we’re hoping in the next few years to break the golden chains and break out into our own family farm. My oldest son is particularly interested in plant genetics. This has been a dream of his for several years. This is by far better than anything for him. This is his Disney World.”

Expo-goers flocked to check out the giant pumpkins and halls full of squash, gourds, tomatoes, dahlias and other produce. They snacked on handmade Popsicles and organic popcorn and filled the fairgrounds halls to listen to talks on seed saving, culinary herbs, resisting GMOs and no-till growing.

Rosalia Asig came from Guatemala and was selling Epic Seeds, collected and packaged by struggling farmers, She heads an organization called Qachuu Aloom, an association working to help farmers empower themselves by saving their native seeds, many of which all but vanished after Spaniards invaded the New World.

“This is important,” she said. “It’s sacred for our culture,”

The expo continues Wednesday and Thursday, with an appearance today by Australian celebrity chef Peter Gilmore, a big booster of cooking with heirlooms, and on Thursday a seed swap, which typically draws a big crowd of people who trade seeds.

You can reach Staff Writer Meg McConahey at meg.mcconahey@pressdemocrat.com or 707-521-5204. On Twitter @megmcconahey.