“I really like to be busy,” Warren Haynes says, and that’s long been an understatement. For two decades, the guitarist/singer has led brawny blues-rockers Gov’t Mule in addition to serving in the venerable Allman Brothers Band, which he plans to leave after this year. He’s also fronted his own soul-rock outfit and joined surviving members of the Grateful Dead—most often Phil Lesh—on the road.

Now Haynes is launching his second Jerry Garcia Symphonic Celebration tour, performing the late Grateful Dead leader’s music with orchestras across the country. Haynes will rejoin Keith Lockhart and the Boston Pops on May 13-14 at Symphony Hall. And, as at their summit last year at Tanglewood, they plan to reprise Garcia signatures like “Dark Star,” “Bird Song” and “Terrapin Station” (originally recorded with strings) as well as his version of Irving Berlin’s “Russian Lullabye.” But Haynes says he also wants to rotate new material into the sets.

“I really wanted to pick the songs that became somewhat magical with the symphony [orchestra],” says Haynes, 54, who was enlisted for the project by guardians of Garcia’s estate—and who plays the Dead guru’s custom “Wolf” guitar at the concerts. “I don’t think every classic rock songbook would benefit from a pairing with a symphony. Actually, I think very few would. But Garcia’s music is unique in that way. It’s steeped in history, and there’s so much influence coming from many different directions. It’s not just one-dimensional pop music.”

Still, the orchestral collaboration didn’t come easy, he says. “In the beginning, it was not just a challenge, but a little intimidating for someone like myself who’s lived in this world of improvisation. Symphonies don’t improvise. They read things to the letter.”

Working with three arrangers, Haynes struck a happy medium, having orchestras drop out or return on cue while his electric band—composed of drummer Jeff Sipe, bassist Lincoln Schleifer and backup singers Alecia Chakour and Jasmine Muhammad—improvises through the spaces. The arrangers also transcribed live Dead recordings for the orchestras, he says, “so it was written out, but from something that was originally improvised.”

Haynes isn’t shy of a conceptual challenge, as evidenced by Gov’t Mule’s latest album. “Shout! is the most diverse record we’ve made,” he says of the fall 2013 release, which strays from the Mule’s pow:er-trio roots with splashes of reggae and punk. But the double album’s unique angle was that Haynes sang the songs on one half before 11 guest vocalists—including Dave Matthews, Dr. John, Grace Potter and Steve Winwood—split turns on the same tunes. And it all began when Haynes thought “Funny Little Tragedy” was a song meant for Elvis Costello to sing.

“Once we had the idea to have one guest, then two guests and three guests, the idea just grew from there,” says Haynes, who gave each artist his original version and made sure that each felt a personal connection with the song. “Some people took it further than others.” In turn, Haynes says he avoided the temptation to redo his versions, but the cameos now influence the way he sings the songs live.

He says Gov’t Mule (rounded out by drummer Matt Abts, keyboardist Danny Louis and bassist Jorgen Carlsson) should return to Boston later this year—and hopefully the same goes for the Allman Brothers Band. So far, their closest shows are both at the Mountain Jam festival in Hunter, N.Y., on June 7-8. Gregg Allman also headlines Lowell’s Boarding House Park with his solo band on Aug. 9—and Haynes notes that Allman, 66, is sounding stronger since his bout of bronchitis curtailed the Allmans’ March run at New York’s Beacon Theater.

Both Haynes and Allman Brothers guitar foil Derek Trucks have given their end-of-2014 notice to focus on other projects, and Haynes says he’d be surprised if the group continued to tour. “This is something the entire band’s been talking about the last two or three years, of picking the right time to go out on a high note,” he says, “and I think most or all of us felt like the 45th anniversary would be the right time to do that.”

Jerry Garcia Symphonic Celebration, featuring Warren Haynes with the Boston Pops, plays Symphony Hall on May 13-14.