They are mostly strangers who don’t share a whit of practice time together until the day of their performance and haven’t had to go through a tryout.

Each of the past seven years, trombone players — some quite experienced and some not so — put on a holiday concert for visitors at the Anaheim GardenWalk, a shopping, dining and entertainment center near Disneyland.

Many have signed up for the gig ahead of time, having heard of the Trombone Christmas through social media, word of mouth and some advertising, but should someone walk in off the street with a trombone in hand, he or she would be welcome to join in — although maybe not in the most prominent position.

Because there are no auditions, the performance is based on trust, said Douglas Grieve, one of the founders of the event.

“Anybody who’s got some talent that they can show, we’re more than happy to include them,” said Grieve, who has been playing the trombone since he was in the fourth grade.

Grieve said no one has ever been kicked out for being out of tune or otherwise not up to snuff, but he ensures that the most seasoned performers take the lead parts.

Trombone players perform at a previous ”Trombone Christmas” at the Anaheim Garden Walk. (Courtesy of Douglas Grieve)

The trombone players are invited to meet on the morning of the performance for the first time for their only rehearsal.

They range from high school students to much, much older, and some are decked out in Christmas garb. About 30 of the 100 or so who typically show up are from the Bones West trombone choir, lending a consistency of experience. The commonality is the desire to play trombone and entertain.

Grieve said trombones go hand-in-hand with Christmas because the earliest heralds were played on the sackbut, an early form of the instrument played during the Renaissance period.

“People want to hear Christmas music in a light brassy way,” he said, noting that the group plays traditional and modern holiday tunes. “If you look at any old Christmas herald illustrations, you’re going to see a trombone or a sackbut. It’s a natural progression into holiday music.”

Songs in the hourlong performance on Dec. 10 will include “O Christmas Tree,” “White Christmas,” Amy Grant’s “Christmas Lullaby” and the Hawaiian-themed “Mele Kalikimaka.”

Grieve said he got the idea for the performance about a decade ago when he played in a Christmas-themed tuba performance at Disneyland.

“I noticed a good chunk of them were trombone players,” said the 57-year-old Garden Grove resident. “I said, ‘Well, if there are that many guys and gals that want to get together to play Christmas tunes, then we can have our own Trombone Christmas.’ ”

Grieve added that trombones allow for a more “harmonious” sound than tubas.

The first Trombone Christmas event was held at the Anaheim GardenWalk in 2009, when about 100 players gathered. The numbers have since fluctuated each year between 80 and 100.

While players can sign up the day of the performance, Grieve urges earlier registration through trombonechristmas.org, where a full schedule for players is also available. He charges $5 a player to cover expenses.

This year, Grieve hopes at least 150 trombone players take part in the event

But if by a stroke of luck far more players join in an act of spontaneity, the group has the potential to break a record, Grieve said.

In June, the International Trombone Festival set the world record with 371 trombone players playing at the same time at Lincoln Center in New York, according to the Guinness Book of World Records.

Robin Weeks-Wynne, spokesperson for the Anaheim GardenWalk, which has struggled with attendance, said the Trombone Christmas has been well-attended over the years and is something center officials always look forward to.

“We are thrilled to showcase the amazing talent of area musicians and hopefully make this a record-breaking Trombone Christmas event,” she said in an email. “We continue to bring this event back each year because the holidays are such a special time. We want to offer guests a unique and exhilarating experience while they’re here, and this is one of our many opportunities to feature arts and entertainment at GardenWalk.”

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IF YOU GO

What: Trombone Christmas

Where: Anaheim GardenWalk, 400 Disney Way in Anaheim

When: 1 p.m. Dec. 10

Cost: Free

Information: trombonechristmas.org

brittany.woolsey@latimes.com

Twitter: @BrittanyWoolsey