The 10th Roots Picnic is coming. What keeps the band together?

There’s a big round number attached to the Roots Picnic this year: It’s the 10th time the Philadelphia hip-hop band led by rapper Tariq “Black Thought” Trotter and drummer Ahmir “Questlove” Thompson will host a multistage shindig at the Festival Pier on the Delaware River waterfront.

This year’s lineup is formidable. Solange, Lil Wayne, Jeezy, Kimbra, Michael Kiwanuka, Thundercat, and Noname will perform as preludes before “Happy” hitmaker Pharrell Williams and the Roots join forces to bring the daylong event to a close.

The leaders of the staggeringly versatile house band for The Tonight Show Starring Jimmy Fallon are proud to have spent a decade kicking off the summer concert season in their hometown.

Booking the fest “gets easier and easier every year,” Trotter says by phone in transit from his home in North Jersey to a Fallon taping in New York. “People know what the brand represents, and they’re happy to be part of it. Still, it being 10 years, we definitely want to make it special, make it feel more celebratory.”

The rapper is particularly hyped about the Black Thought and J. Period Mixtape segment, featuring guest spots by Fat Joe, Mobb Deep, and original Roots keyboard player and producer Scott Storch.

In 2016, the Pharrell spot was occupied by R&B star Usher, with whom the band has continued to play live, including a headlining spot at the New Orleans Jazz & Heritage Festival.

“Last year, we told Usher: ‘Listen, it’s a one-night stand. You have to go home after this.’ But he never took no for an answer,” Thompson says in a separate interview from backstage at Fallon’s 30 Rockefeller Center set, where the musician was prepping for a skit with Dwayne “The Rock” Johnson.

“We’re doing about 20 gigs with Usher this year, and, more than likely, we’ll do an album together. It’s really fun. I enjoy doing it,” the drummer says. “I’m just hoping that after this year, Pharrell’s not like: ‘Now we’re a group!’ ”

This year marks another milestone for Trotter and Thompson, both 45. Thirty years ago, in 1987, while students at the Philadelphia High School for Creative and Performing Arts, they formed their first group. Initially, they were Radioactive, then — as they started busking at the intersection of Fifth and Passyunk — the Square Roots and, finally, the Roots.

(The new company with which they’re developing two TV shows for Amazon — an animated children’s series and a documentary-style show based on Shea Serrano’s The Rap Yearbook — is called Passyunk Productions.)

Black Thought and Questlove have been constants since then, and the eight-piece lineup has been steady since Mark Kelley replaced Owen Biddle on bass in 2011. The rest of the band are James Poyser and Kamal Grey on keys, guitarist Captain Kirk Douglas, percussionist Frank Knuckles, and Damon “Tuba Gooding Jr.” Bryson on sousaphone.

And what has the mood on the show been now that the late-night ratings wars have heated up, with CBS’s Late Show with Stephen Colbert now frequently topping the formerly dominant Tonight?

“I’m not touching that with a 10-foot pole,” Questlove says with a big laugh. “I come in every day doing the same quality work I did when we were underdogs, first place, second place, whatever. Somebody once teased me by saying, ‘Questlove does everything like he’s thinking about his Wikipedia entry.’ I laughed, but who wants to have a spotty report card? I’m always going to do quality work, no matter what happens.”

The secret to the Roots leaders’ staying together has been spending time apart. Black Thought credits “constant reinvention, keeping an ear to the street, mutual respect, and professionalism — and separate tour buses.”

Like Questlove, the rapper has plenty of sidelines. “I try to stay engaged in the arts and in music,” he says. “It’s time-consuming, but I feel it’s worth it for my sanity.” He does sports voiceover work for the NBA and, most recently, the NFL draft. He’s working on a solo album called The Talented Mr. Trotter and on a memoir. “I can’t have Questlove being the only member of the Roots being an author.”

Black Thought will host two comedy shows Friday with JB Smoove at Punch Line Philly, before Questlove deejays across the street at the Fillmore. And on Saturday morning, the rapper will lead the 5K Roots Rock Run in Germantown to benefit community health programs.

Thompson cracks the same “separate tour buses” joke, and adds: “It’s like an open marriage. You can satisfy your itches and do side projects, but you can always come home, too. We’re in institution range. Why leave now?”

The drummer and gourmand is putting finishing touches on his fourth book (his third was titled Something to Food About) which he describes as “a manual to describe the process of creativity.” (Hint: It involves practice and hard work.)

Other Roots projects: The band is working on music for director Kathryn Bigelow’s coming Detroit, about the 1967 riots. And after tasting Broadway success with involvement in Fela! and Hamilton, they’re collaborating with writer-director John Ridley on a musical based on George Schuyler’s Harlem Renaissance-era satire Black No More.

Trotter says “it’s definitely a bummer” that, after hosting the Fourth of July concert for eight years on the Ben Franklin Parkway during the Nutter administration, they’re no longer involved. “Hopefully, we’ll make a grand return at some point.”

“Everything we do in the city of Philadelphia is a labor of love,” says Questlove, hinting that starting next year, the workaholic band will begin an annual Independence Day residency elsewhere. “There’s a city that appreciates us, I’ll say that.” (Meanwhile, after it debuted last year in Bryant Park, there will be no Roots Picnic NYC this year,  but Questlove says it will return in 2018, along with the likely debut of a Roots Picnic Japan.)

When will there finally be a new Roots album to follow 2014’s ... And Then You Shoot Your Cousin? It’s going to be called Endgame and will probably come out in early 2018, says Questlove.

Working 44 weeks a year on Tonight has forced the group to grow musically, he says. “You’re forced to be in one place for a 10-hour period. You have to be on standby, like a doctor.” Over eight years, the group has written thousands of seven-second instrumentals as lead-in and lead-off music, and the band has parts of more than 300 songs in the works for Endgame. “And we only need 14,” Questlove says.

One of the major changes in the Roots world is the loss of their longtime manager, Richard Nichols, who died in 2014. He “was very much a part of what made the Roots the thinking-man’s hip-hop band,” says Trotter. “One thing that Rich is not there to do,” Thompson jokes, “is stop us from recording.”

Working on Tonight, Questlove says, “has made me a smarter songwriter, and way smarter producer. When I listen to the music we’re recording for this album, and then the previous 16, I’m like, ‘Man, how did we get away with this? All we’re doing is grooves, there’s no melody.’ Now, I’m thinking like a disciplined songwriter. I don’t want to lay a hyperbolic statement on you, but I feel like this will be our first record.”

The Roots Picnic at the Festival Pier, 601 N. Columbus Blvd, at noon Saturday. $75. 215-922-1011. RootsPicnic.com.