Once celebrated mostly in Irish enclaves such as Boston, St. Patrick’s Day is becoming more mainstream — and more commercial.

Far beyond green bagels and beer, retailers as varied as Old Navy and Office Depot are using the occasion to spur sales during a lull in the calendar, between holidays with more historic sales ties.

“St. Patrick’s Day has always been a popular holiday, but it hasn’t always been a retail holiday,” said Ellen Tolley, a spokeswoman with the National Retail Federation in Washington, D.C. “In the last several years, we’ve seen an increase in St. Patrick’s Day merchandise, from green plastic hats to traditional Irish music and cookbooks. We’ve seen a lot of momentum in the last couple of years building up toward St. Patrick’s Day.”

Driving the interest, retailers said, is a larger number of non-Irish celebrating the holiday. About 110 million consumers will celebrate St. Patrick’s Day this year by doing such things as wearing green, cooking traditional Irish dishes or dining at an Irish pub. Nearly 20 million will decorate their homes or offices with St. Patrick’s Day merchandise, according to the federation.

Evidence of the holiday’s retail emergence is mostly anecdotal though: The major industry groups haven’t tracked St. Patrick’s sales as they have major sales holidays such as Christmas.

“Valentine’s Day is over and Easter hasn’t arrived, so it’s a good time to promote a holiday in between,” said James Lowry, a retail marketing professor at Ball State University in Indiana.

Old Navy Inc., the hip clothier owned by Gap Inc., is selling St. Patrick’s Day T-shirts, hoping to duplicate some of its success during recent summers selling a line of shirts specifically for July Fourth. Guinness USA Inc., which imports the dark porter brew made in Ireland, began airing commercials months ago to spur sales for the holiday. And Vermont-based Brueggers Bagels, which began selling green bagels at its Pittsburgh location a decade ago, has slowly expanded into other markets. This year, it will bake 2,200 dozen green bagels in 15 markets.

“St. Patrick’s Day is becoming a big deal,” said Christine Bryan, director of marketing for Brueggers. “It’s a holiday that gives people a reason to go out and have a good time.”

Retailers have been promoting St. Patrick's Day to boost sales. Parade-goers, from left, Megan Hauswirth, Kelsey Meyers, Ashley Opheim and Kayla Bell, bought accessories to celebrate the holiday. They attended a St. Patrick's Day parade Saturday in Emmetsburg, Iowa.