Sarah Jarosz and the Milk Carton Kids aren’t just on tour together. They’re performing together as a single act, an idea that came to the group of friends last year. “We opened for Sarah and were looking for a song to do for the finale,” says Joey Ryan, who makes up one half of the Americana duo The Milk Carton Kids. “She said, ‘Why don’t we do your song, ”Years Gone By?”’ So we sang the first line, and we stopped and started laughing about how exhilarating and disorienting it was to sing that three-part harmony, and about how we couldn’t get to the second line and had to stop and start over because we were all amazed. At that point, it was probably predestined to grow into a proper collaboration.”

Thus, the In Collaboration tour with Ryan, his bandmate Kenneth Pattengale, and Jarosz was born. Instead of the Kids playing their own set, Jarosz playing hers, and then coming out for a combined finale as they have done before, they’re performing the entire concert together. Everyone will be playing and singing around one microphone, including Jarosz’s regular cellist, Alex Hargreaves, her fiddler Nathaniel Smith, and an independent upright bass player, Samson Grisman.

“There’s a wealth of excitement and of different songs we want to sing together,” says Jarosz, who plays the mandolin, guitar, and banjo in addition to singing and writing her own songs. “We’ll incorporate a lot of our own material, but we’ll also do some new covers that we’re working up for this particular show.”

But that’s not all. “We’ve written a handful of songs together that no one’s ever heard before,” Ryan reveals.

Ryan, Pattengale, and Jarosz will sing tracks from Jarosz’s catalog, including last year’s Build Me Up From Bones — which was nominated for two Grammys, including Best Folk Album — and the Kids’ own impressive catalog; they’ve released three studio records and a live album in the past four years. The duo also won an Americana Music Association Award last month for Best Duo/Group of the Year. For two of the rising talents in the world of roots music, this amounts to one heck of a showcase of not only what they can do with their own material, but how they can add life to each other’s catalog as well.

That is not an easy thing to pull off since musicians tend to guard their music with their lives, but things seem to be going well so far. “Any time we’ve ever tried to do a new song together, it pretty much has fallen into place instinctively,” says Ryan. “I can’t imagine that’s going to happen for all the songs we’ve selected, but everybody seems to be coming from the same place so we haven’t really butted heads about anything yet.”

“Up to this point, the biggest challenge we’ve had has been narrowing down the material,” Jarosz concurs. “There haven’t been a lot of challenges, to be quite honest, because we’re all on the same page as far as what our visions are for how the show’s going to play out.”

The blending of their styles promises to be one of the evening’s most vital components. The bulk of Jarosz’s material — particularly on Bones — combines elements of Americana (“Over the Edge”), bluegrass (“Fuel the Fire”), and country (“Mile on the Moon”) and is led by Jarosz’s spellbinding vocals. She engages the listener with razor-sharp insights into the nature of the human condition and dares you to come with her to places that are raw, honest, and sometimes uncomfortable. Her songs are rich, fully fleshed-out experiences.

Ryan and Pattengale follow a slightly different tactic. They are firmly grounded in the ways of classic folk, as 2013’s The Ash & Clay demonstrates. The entirety of this 12-track record comprises songs that feature the two singers and their guitars and nothing more. It’s all about simplicity. But the combination of the three reaches into a more complex territory.

“One thing that remains to be seen is what the change in dynamic will be in the in-between-song sections where Kenneth and I usually allow ourselves incredible improvisational freedom in the banter section,” Ryan laughs. “Having a third, and then a fourth, fifth, and sixth voice gathered around a microphone, our instinct is to sort of go off the rails, verbally. So that’ll be interesting and fun. I don’t know though, maybe it won’t work.”

And for all anybody knows, this collaboration might be a bust, but at least they’re having a good time. “It’s inspiring and fun to get thrown into these different collaborations and get pushed in different ways than you might have expected going into it,” Jarosz says. “I think that’s certainly what this has been doing for me so far, and I expect it will continue to be that way on tour. It will be a journey for all of us.”