Tift Merritt starts things off on the Fort Stage as the first performer Saturday morning at George Wein’s Folk Festival 50.

The Providence Journal / Kathy Borchers

NEWPORT — “It’s the most predictable story told,” The Avett Brothers sang Saturday at George Wein’s Folk Festival 50; “In with the new, out with the old.”

That was how the first day played out. Not that the old guard wasn’t represented — Ramblin’ Jack Elliott, singing on his 78th birthday, gave a weathered dignity to chestnuts such as “Freight Train” and “Don’t Think Twice It’s Alright”; Mavis Staples got everyone from Elliott to the hipster roadies dancing to her mix of gospel music and Stax soul.

But the day belonged to the young acts at Fort Adams. Singers and players who were a quarter of the age of the closing act, Pete Seeger, made their mark on the crowd and on the tradition of folk at Newport, always an elastic concept.

Young singer-songwriters made a mark as well. Ben Kweller’s shaggy, amiable mix of introspective tropes and jam-band grooves charmed a big crowd on the second stage; Iron and Wine, the performing name of singer-songwriter Sam Beam, chilled the second-stage crowd with simple, spare stuff.

The third stage was where the volume was for most of the day, with Langhorne Slim getting things off to a foot-stomping start with electric Delta-inspired blues. The Avett Brothers were the hit of the early going on the main stage, with high, clear bluegrass-inspired harmonies and high-octane, foot-stomping tempos on songs such as “Left on Laura, Left on Lisa,” then shifting on a dime to lovely ballads such as “The Ballad of Love and Hate.”

Rhode Island’s own Low Anthem made their Newport debut on the third stage, lowering the temperature in the audience with the lovely harmonies of the opener, “Charlie Darwin,” and moving on to the slow, sinister rock crawl of “To Ohio.” Ben Knox Miller, Jeff Prystowsky and Jocie Adams switched among a bevy of instruments ranging from electric guitar to drums to bowed crotales to evoke a range of emotion. Billy Bragg, who worked wonders on the main stage earlier, made a point of heading over to see Low Anthem and later pronounced them “really beautiful. ... The great music, it’s not what you play; it’s what you don’t play.” (For his part, Miller said Bragg’s comments “killed me.”)

Indie-rock darlings Fleet Foxes entranced the main stage audience with a combination of head-rush harmonies and psych-rock grooves, and The Decemberists, who generally flit in and out of the folk tradition, continued to do so. A mostly acoustic “Isn’t It a Lovely Night” had a classic vibe, while the suite-like “Valencia,” started off with harpsichord and ended up with anthemic distorted guitar made even more celestial by a glockenspiel hook.

The Oregon-based Decemberists also pulled of a piece of high theatre during “Cautionary Song,” with half the band playing the song and the other half walking through the audience with marching percussion to set up in the middle of the crowd for a humorous reenactment of Bob Dylan going electric in 1965.

All that said, the day’s highlight came at the end, with the cross-generational outpouring for folk icon Pete Seeger, who celebrated his 90th birthday this year.

Bragg set the crowd off in the afternoon with a combination of well-observed detail (“The Space Race Is Over”) and political stridency (“Dreamed I Saw Phil Ochs Last Night”), the latter quality only gaining dimension as Bragg ages. But he was deeply appreciative of the chance to share a stage with Seeger. So was Tom Morello, the Rage Against the Machine guitarist who performed a politically-charged solo set as The Nightwatchman, who called Seeger “the living embodiment of justice and everything that is good about America.”

“It’s unbelievable,” said Jeff Prystowsky of The Low Anthem.

Seeger was preceded on the stage by a tribute video featuring George Wein, Arlo Guthrie, Joan Baez and more, while the man himself ambled on with his grandson, Tao Rodriguez-Seeger (who updated the folk tradition with electric guitars and drums with his own band on the third stage earlier).

And the day ended with a sing-along with the Seegers, Rodriguez-Seeger and his band, Bragg, Americana pioneers Gillian Welch and David Rawlings (who played the main stage earlier), and members of The Decemberists, Fleet Foxes, Low Anthem and more, for a run through “This Little Light of Mine,” “Guantanamera” and of course “This Land Is Your Land.”

It wasn’t the equivalent of the All-Stars crowding around Ted Williams at Fenway Park, but — actually, yes it was.

The cross-generational appreciation extended to the audience, too. As The Decemberists played, George Pires, 67, of Providence, said he enjoyed them, as well as Fleet Foxes. “I like music generally anyways,” he said; “it doesn’t matter who’s playing it.”

And Karina Argot, 21, drove from New Jersey to see The Avett Brothers; thanks to the traffic, she missed them by hours. But as Seeger played on, she said, “This is making my life right now. Who could ask for more?”

And the generational mix worked; the attendance was 9,200, the most since Bob Dylan returned to the festival in 2002.

rmassimo@projo.com