"These are the immigrant populations who wanted to improve their lives, just as my grandparents did," said Chris Alonzo, president of Pietro Industries.
While today's growers blend lab science with modern techniques for temperature, humidity, and carbon-dioxide control, harvesting is still by hand, an arduous, on-your-feet-all-day job for successive waves of mostly foreign-born laborers.
Doing work that is dirty and time-sensitive - mushrooms grow in a loamy mixture and double in size every 24 hours - workers begin at minimum wage and earn more through piece work, filling three to five 10-pound boxes an hour.
Alonzo's grandfather, Peter "Pietro" Alonzo Sr., whose family came from Abruzzi, Italy, began mushroom farming in Kennett Square during the Great Depression. Through the 1930s, approximately 500 mushroom houses were built within 10 miles of Kennett Square. The area had good access to major markets. Horse farms provided abundant manure for compost.
Alonzo, 44, has an economics degree from Allegheny College. Pietro Industries had four grow rooms when his father, Peter Alonzo Jr., joined the business in 1967. Today it has 53 rooms and 150 employees, making it the sixth-largest of the county's 60 mushroom farms.
A tour of his farm last week found Mexican workers watering scores of 5-by-60-foot compost- and peat-covered alleys, stacked like bunk beds inside barn-like grow houses and bristling with creamy white mushrooms. Heaps of cut-mushroom stems covered a damp floor.
"I'm not bilingual, but I can get any farm conversation done," Alonzo said in an aside, while chatting in Spanish with the workers.
Driving a few miles in his blue Chevy Tahoe to look in on his new, state-of-the-art grow house, Alonzo recounted more mushroom lore.
After the Quaker farmers and some of Irish descent, he said, Italians - former stonecutters and silk mill workers laid off when the quarries and mills closed - arrived as laborers and later owners.
The workforce of the 1950s included white and African American "local kids," most of whom did not want livelihoods in mushrooms, said Alonzo. When they found better opportunities they moved on. Mushroom jobs were non-union, and with the exception of one company, Kaolin Mushroom Farms, still are.
Puerto Ricans, including former sugar cane cutters who were born on the island as U.S. citizens and came to the mainland speaking Spanish, were recruited during World War II. Their Latino influence still permeates.
At Pietro's new grow house - a huge, $10 million, climate-controlled facility - the laundry hamper for workers' pants is labeled pantalones; shirts go in the camisas bin.
Puerto Ricans made up the majority of the workforce from the 1950s into the '70s.
Then Puerto Rican workers began to organize, demanding "higher wages, overtime compensation, and improvements in their working conditions," according to a 1997 report on the industry by Indiana University of Pennsylvania professor Victor Garcia. "Their organizing efforts were met with strong resistance from the growers, who . . . systematically dismissed them and hired Mexican migrants."
In the 1980s, as some Puerto Rican workers moved into management or left the business, many entry-level jobs were filled by migrants from Mexico's Guanajuato state, often recruited through kinship networks.
Most were single men, with or without guest-worker permits. They left families in Mexico and lived together in often rundown "mushroom camps" provided by the growers. Some of the camps were targeted by Friends of Farmworkers, a public-interest law group.
The federal Immigration Reform and Control Act of 1986, which granted amnesty to undocumented immigrants who had lived in the United States since 1982, enabled migrants to establish legal residence in the U.S. Many sent for their wives and children and began establishing a permanent Mexican community in Chester County.
"The change in housing patterns is significant," said Friends of Farmworkers general counsel Art Read. "Kennett became an anchor community for Mexican migration."
Enrollment of migrant children in borough and surrounding schools jumped - from 253 in 1989 to 602 in 1995.
From 2002 to 2005, the county's Mexican population doubled, to more than 10,000. From 2000 to 2010, the overall Hispanic population rose from 3.7 percent to 6.5 percent.
It seemed inevitable that Mexican laborers would rise to become owners - and about six of them have.
Martin Ortiz, 47, of Kennett Square, is one.
Born in Toluca, Mexico, Ortiz was 16 when he came alone to the U.S. in 1983. He got permanent residency in 1987, and citizenship in 2001. He has two sons. One is a pre-veterinary student at Pennsylvania State University. The other is a Kennett police officer.
For more than two decades, Ortiz worked for others, picking, packing, driving trucks. With his wife, Norma, helping him he added a sideline cultivating shiitakes, which grow in decaying logs. With financing and some savings he began buying buildings to grow white button mushrooms.
Five years ago, he opened Liberty Mushrooms. Its stylized Statue of Liberty logo is his nod to a dream realized.
"I love the United States," he said, "a free country," with opportunities for his family.