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When Helena Hackman and Baptist John Ott immigrated to the United States from Bavaria 140 years ago, they brought with them seeds from the morning glory and the German pink tomato. The Otts’ great-grandchildren have kept the family tradition—with a modern twist. They founded , a nonprofit dedicated to preserving heirloom and open-pollinated seeds, and making them available worldwide.

Some 13,000 members pay a $40 fee to trade heirloom seeds through a catalogue or online. “You can look up things that have been growing in your area or you can look for that really exotic seed,” says public programs manager Shannon Carmody.

It’s just one of several such groups popping up online. Tens of thousands of gardeners exchange heirloom varieties, or seeds passed down through the generations and pollinated in the open air, via the Web, helping to promote crop diversity. Today the top 10 seed companies control 67 percent of the branded seed market. At the same time, by some calculations, humans have gone from relying on 7,000 plant types to consuming a mere 150.

On , a free swap founded by John McKissack two years ago, gardeners buy, sell, or barter for what they want. “There are peppers that taste like candy caramel sugar, and you can’t buy those [at the store],” he says. “You start getting into food that your grandparents had—that you’ve never had in your life—and you have your choice of delicious food. That opens up a whole world that I just think is cool.”

This story originally ran as “Planting the Past” in the March-April 2012 issue.