The band they originally booked as headliner backed out because of a wedding. The group that did wind up at the top also backed out, then recommitted. About 80 other acts were ruled out simply by the fact that Bonnaroo in Tennessee landed on the same weekend this year. And organizers are still debating whether Macklemore should have been considered.

So it goes with Rock the Garden. The annual concert outside Walker Art Center returns Saturday with another instantaneously sold-out lineup — the assembling of which was anything but fast and easy.

"It seems like every year, there's at least one point in the process where we really start to fret and say, 'Oh, God, I don't know if we're going to be able to pull it off,' " said Philip Bither, the Walker's senior curator of performing arts.

Time and budget constraints hinder Rock the Garden's booking process more than most big concerts. Then there's the simple challenge of getting two of the Twin Cities' most finicky arts organizations to agree on the right bands to represent them at their biggest one-day event of the year.

Planning for RTG "pretty much starts while we're watching the bands the year before," explained Jim McGuinn, program director at 89.3 the Current, which has co-organized the event with the Walker each year since 2008.

"We're definitely an opinionated group of people," McGuinn noted.

Doug Benidt

The two organizations assemble a tally of about 100 possible acts. That includes the usual pipe dreams (Radiohead, Prince), plus perennial favorites who have yet to play RTG, including this year's pair of Minnesota-bred acts, Bob Mould and Low. In keeping with the Walker's experimental aesthetic, there's usually a short list of left-field surprises, evidenced by Tune-Yards last year and Dan Deacon this year.

The list then gets updated with acts that have released buzzed-about albums. Metric is the prime example of that this year.

The Canadian synth-rock band already had ties to the Current and its parent Minnesota Public Radio, and it booked a date with MPR's "Wits" the night before RTG this year. Still, Metric nearly had to pull out when it was offered a major tour-opening slot (a tour that fell through).

"They were a shoo-in, but even then it comes down to timing," said McGuinn.

Some of the other names that came up included the Yeah Yeah Yeahs, Alabama Shakes, Vampire Weekend and Michael Kiwanuka (who wound up being booked for the RTG after-party at First Avenue). Also in the mix were newly minted "Thrift Shop" hip-hop hitmakers Macklemore & Ryan Lewis, whom McGuinn said he viewed as "a hip sort of indie-rap act like Atmosphere."

The Walker's staff saw otherwise. "We try to avoid anything that might come off as a one-hit wonder," explained Doug Benidt, assistant curator at the Walker in charge of RTG's production. "I'm still catching grief for picking MGMT," which delivered an infamously lackluster performance at RTG 2010.

By October or November, McGuinn and Benidt are hard at work putting in calls and checking whether acts are available. Said Benidt, "There's a lot of work and especially a lot of luck involved."

The show is always the same Saturday in mid-June, so organizers have no backup date to offer bands. What's more, a summertime Saturday is a top payday for bands of the rock-fest ilk, but RTG usually offers less than optimal rates. Performers instead take the inherent Current airplay for trade, as well as the satisfaction of raising money for the two nationally recognized nonprofit organizations (last year's RTG cleared about $32,000 after covering $690,000 in costs, per the Walker's annual budget report).

It certainly helps that the Current's reputation is recognized by the bands asked to play RTG, said Warren Christensen, who works with both Metric and Silversun Pickups as the head of the promotions department at Q Prime Management and Mom + Pop Records in Los Angeles.

"The station is typically one of the first to play an artist, and as an artist when you roll in to town and have a great show early in your career you take note," Christensen said, pointing to Saturday's concert as another big stepping-stone for his bands.

"Both Metric and Silversun Pickups want to headline the Arena in the Twin Cities someday, and shows like Rock the Garden gives us a chance to do that."

That's exactly what organizers like to hear -- and to pass along to bands who might get invited next year.

"The good news is, I think word is getting around among the bands and their agents that it's a great gig," said Benidt. What makes the process harder, he said, "is we feel more and more pressure each year to keep the momentum going."

Chris Riemenschneider • 612-673-4658 • Twitter: @ChrisRstrib