Zach Williams, left, a worker at the Zweck family farm in Longmont, hands a freshly picked bunch of basil to Tom Zweck, who will bind it with a rubber band. In addition to the basil, top center, the Zwecks grow bell peppers and cherry tomatoes. (Photos by Andy Cross, The Denver Post )

LONGMONT — Four generations of the Zweck family have farmed on the west edge of town, but when the fifth opted out, the 230-acre operation seemed doomed to development.

"The city limits are right on our fence," said John Zweck, whose great-grandfather George Zweck purchased the property in 1863 from a Civil War veteran.

Instead of selling their riverfront property to developers, the Zwecks offered their land to Boulder County's Open Space Agricultural Resources Division.

The county bought an option, and in 20 years, the land — hemmed in by subdivisions, strip malls and the Vance Brand Municipal Airport — may be rolled into the agricultural preservation program.

Started 30 years ago, the

"I know a lot of local farmers," said Connie Zweck, who runs the organic-vegetable operation with her husband, Tom, John's brother. "Most are farming on open space. They don't own their land."

Open-space tenant farmers — some first-generation farmers and some whose families have tilled land in Boulder County for six generations — raise crops such as sunflowers, barley, sugar beets, millet, oats and pinto beans.

They produce enough vegetables to feed 110,000 people, enough wheat to feed 78,000, and enough hay and corn to produce beef for 50,000 — selling to farmer's markets, grocery stores, breweries and the livestock industry, said Boulder County Parks and Open Space director Ron Stewart.