Sweetgreen’s co-founders, from left, Nicolas Jammet, Nathaniel Ru and Jonathan Neman. (Jeffrey MacMillan/JEFFREY MACMILLAN)

Back in 2009, when the founders of Sweetgreen opened their second store in Dupont Circle, they found themselves in over their heads.

Unlike their first salad-and-frozen-yogurt restaurant in Georgetown, which had achieved instantaneous success, Dupont Circle was proving a harder sell. For one, the three founders — all recent graduates of Georgetown University — didn’t have any real ties to the neighborhood.

So they thought they’d try some music. The trio went to Guitar Center, bought a huge sidewalk speaker and began blasting music: Al Green, Daft Punk and everything in between.

“We wanted people to know that this wasn’t just about healthy food,” said Jonathan Neman, one of the company’s co-founders. “There are real people behind this.”

In the six years since its founding, the company has become a home-grown success story. The business, started by three 20-somethings with recipes they’d perfected in their dorm rooms, hit the scene in the midst of the economic downturn.

Since then, District-based Sweetgreen has started its own music festival and established a charitable organization. There are 17 shops now, with plans to open locations in Boston and New York in coming weeks.

“We started this company because we wanted to solve a problem: We wanted better food,” co-founder Nicolas Jammet said.

Those early jam sessions in Dupont Circle led to regular parking lot parties and, eventually, to the annual Sweetlife Festival at the Merriweather Post Pavilion in Columbia.

“It literally went from 1,000 people in a parking lot to 20,000 people at one of the most iconic venues in the region,” Neman said.

The music festival, now in its third year, most recently featured three stages with bands such as Passion Pit, Phoenix and the Yeah Yeah Yeahs.

“They have successfully created a hip identity that people can relate to,” said Seth Hurwitz, co-owner of the 9:30 Club and booker for the festival.

Set up during the recession

Neman, Jammet and fellow co-founder Nathaniel Ru came up with the idea for Sweetgreen while they were students at Georgetown.

“All of us had an entre­pre­neur­ship bug,” Neman said. “Senior year, we decided to start something that we really wanted. So as everyone else was doing senior week activities, we had our hard hats on.”

The trio opened their first Sweetgreen store in August 2007, three months after graduating from college. The hardest part, they say, was securing funding for the 560-square-foot restaurant.

In the end, the co-founders cobbled together $300,000 from investors and received a $50,000 loan from the Latino Economic Development Center.

In some ways, analysts say the timing of the restaurant’s opening couldn’t have been better. The country was about to enter a deep recession, and consumers were looking for affordable, healthy dining options. Even as higher-end establishments floundered, quick-service eateries seemed to be doing okay.

“Ever since the recession started in 2007, the restaurant industry has not been doing very well,” said Bonnie Riggs, a restaurant analyst for the research firm NPD Group. “We’ve never seen weakness of this magnitude, but the real bright spot in the industry has been fast-casual.”

For a few months, Sweetgreen was the only salad-centric fast-casual restaurant in town. That is, until November 2007, when New York City-based Chop’t opened up shop in Penn Quarter.

“We’d always tried to distinguish ourselves from [Chop’t],” Neman said. “But with them coming to the market so early on, we really had to focus on what made us different.”

The company began offering more locally grown ingredients, such as kale, and began Sweetgreen in Schools, a volunteer program that focuses on nutrition and sustainability education at nearby schools.

Today, Sweetgreen has annual revenue of more than $25 million, with sales rising about 50 percent every year.

Little surprises

“Random acts of sweetness,” as the company calls them, come in all shapes and sizes.

On rainy days, employees have been known to cover nearby bicycle seats with shower caps, and attach cheeky notes (“We’ve got your butt covered.”) with gift cards. They also dole out freebies to loyal customers, Twitter followers and increasingly, to hybrid vehicles that have received parking tickets.

In February, Sweetgreen introduced a rewards app that allows customers to pay for their orders using a smartphone. More than 20,000 people have downloaded the app, which now accounts for about one-fifth of all transactions.

Eventually, the founders say they hope the program will allow them to offer digital perks such as recipes, giftcards and play lists to frequent customers.

“We can look at our data and say, ‘We noticed you really love avocados, so we’re sending you a case of avocados,’” Neman said. “Or, ‘You always get the same dressing. Here’s the recipe for it.’ ”

The company continues to evolve, its three founders say. But they’re not quite sure what’s next.

“The thing is, each of our ideas has grown out of our core business,” Jammet said. “We want anything else we do to be just as connected to our community and our customers.”