What does a singer-songwriter sound like before he is filling 5,000-seat auditoriums?

Do those early songs, perhaps available on narrowly distributed, self-released CDs, betray the future? Do early performances, maybe at coffeehouses and small clubs, hint at what is to come?

Garrett Soucy, a 26-year-old singer-songwriter who leads the Knox-based group Tree By Leaf, inspires such questions because, by all available evidence, he fits the “before” picture. Soucy, some veteran observers say, has the talent – and potential to keep growing creatively – to lead his band to that national stage.

A mostly folk group, Tree By Leaf has released three full-length CDs and two EPs, and the band is now recording its fourth album. Soucy has also recorded a solo album, and has begun to write poems, short stories and essays.

That kind of output, and the steady improvement in the songs, has some listeners pricking up their ears and keeping their eyes trained on Soucy’s next move.

And that next move comes in a performance at 7 p.m. Saturday at Rockland’s Lincoln Street Arts Center.

So far, the band has leaned on Soucy’s acoustic guitar and his fine vocals (reminiscent of a young Jackson Browne, or of Whiskeytown-era Ryan Adams), his wife Siiri’s ethereal and smoky harmony voice, and Cliff Young’s harmonically rich and subtly melodic piano backing.

On a cursory listen, Tree By Leaf’s sound would land them in the folk bin at most record shops.

But many of the songs on the band’s “Postcard From Rome” (2003) and Soucy’s solo record, “out a room, through the window” (2003) are more complex than the traditional folk structure, and cry out for more instrumentation, more colors and layers.

The Rockland show will be a sort of coming-out party for a new version of Tree By Leaf, in which an electric guitar, bass and drums will be added on some songs.

Though Soucy is steeped in folk, that may be more accident than choice. The son of a Baptist minister who preached at various churches around Maine, Soucy was allowed to listen only to classical and Christian music as a child. Later, in high school, he discovered Joan Baez, Van Morrison, Creedence Clearwater Revival and Leonard Cohen, music that was palatable to his father’s strict moral code.

Married for five years, the Soucys consider themselves Christians, but do not worship in a Baptist church. Soucy and pianist Young, 29, met while both were working at Fair Haven Camps, a Christian summer camp in Brooks. Soucy and his wife both attended a Christian college in Florida.

The Soucys live in Knox and Young lives in Brooks, west of Belfast.

Soucy’s songs are rife with Biblical imagery.

“It’s inevitable that our lyrics will be religious,” he says. “That’s what I’m interested in.”

But Tree By Leaf’s songs won’t necessarily get played on Christian radio stations. The chorus of one tune prominently features the “s” word. Soucy rejected the Christian music label in part, he says, because “I felt like there were so many demands and expectations” on the part of that audience.

Remarkably, given his self-assured writing, singing and playing, Soucy did not pick up a guitar until he was a freshman in college.

“He started writing songs immediately,” Siiri Soucy says.

Young remembers being blown away by Garrett’s first compositions.

“We’ve always known there was something really, really special about Garrett’s songwriting,” he says. “They’re just unbelievable. He’s like a never-ending well of great songs.”

After quitting his job as a behavorial specialist last month, Soucy penned eight new tunes in two weeks.

“He’s not writing folk ditties any more,” his spouse says of the compositions’ growing complexity.

While many of the songs have melodic hooks and strong, singalong choruses, the lyrics are the heart of the compositions.

“I really like lyrical content,” he says, “people investing in the written word.”

The lyrics are engaging on their own, almost like poems, such as this part of “1,2,3,” from “Postcard From Rome”:

How did this river get here, while I just was speaking? Was it the dam of your eyes? That thing is always leaking. Then, we touched both of our wrists, when they all stopped bleeding. I could ask you one more time, but that would be pleading. Wake up. It looks like the morning has come. Now and then, everyone jumps the gun.

Joel Raymond, a WERU-FM host who features adult contemporary rock music, heard something in Soucy and Tree By Leaf and offered his assistance. Raymond, a live music promoter in Maine for 30 years, became a sort of mentor to the budding singer-songwriter two years ago.

“There’s nothing stopping the guy,” Raymond says. Soucy brings a literate approach to songwriting, while also having “the quality of great melody.”

Raymond is hoping to help land Tree By Leaf songs on radio stations that use the adult alternative album format. Adding more instrumentation to the mix will help, though it is not driven by Soucy’s desire to bring the band to a larger audience.

Sara Willis, who spins contemporary singer-songwriters on the “In Tune By 10” show on Maine Public Radio, is also a fan of Tree By Leaf.

“The first record they put out made me sit up and take notice,” she recalls. Soucy is “very gifted and talented, young and still finding his way. He has to try on all the pants in the store before he finds the ones that both fit and suit him at the same time.”

The expanded Tree By Leaf is working on a new record at bass player Ezra Rugg’s studio in Freedom. Nick Cody is contributing electric guitar parts, and Jason Dean is playing drums.

The three new musicians will join the Soucys and Young on several songs at the Rockland show.

“We’ve recreated some of the older songs,” Siiri Soucy says, giving the band the opportunity to break out of its self-imposed spare sound.

The first plunge into an electric sound came, Soucy says, while playing a house party earlier this year. Other musicians failed to make it, and he had left his acoustic guitar at home, so he stuck with an electric for the night.

“People dancing to Tree By Leaf music was not something that I ever expected,” he says. “We couldn’t go back after that.”

Tree By Leaf performs at 7 p.m. Saturday, May 15, at the Lincoln Street Arts Center in Rockland. Tickets are available at Wild Rufus in Camden, Mr. Paperback in Belfast and at the door. For more information about Tree By Leaf, visit www.treebyleaf.org or write www.garrettsoucy.com. Tom Groening can be reached at 236-3575 and groening@midcoast.com.