Another Boston institution has set a closing date.

Vendors at the Boston Flower ­Exchange in the South End have been told they need to move out by the end of the year, to make way for a new owner at the 5.6-acre site in the South End.

It’s still not clear who that new owner will be, or what they will put there. When the building went up for sale last year, a bidding war among big-name developers drove the price north of $40 million, according to people familiar with the deal. But closing the sale has taken longer than expected, said Joe Cefalo, an attorney who sits on the Flower Exchange board and is handling the deal.

“It’s a complex situation, more complex than a regular straight real estate deal,’’ said Cefalo, who has declined to name the buyer. “I’m hoping it’ll wrap up in the next couple of months.’’

In the meantime, the Flower Exchange’s 13 vendors — who sell flowers to retail stores — have been wondering about their future. The prospect of a sale has been hanging over the place for a year now, and leases were set to expire at the end of 2016. Vendors asked the exchange’s board for guidance, Cefalo said, and the board decided to let the leases run out.

“It’s only fair that we’re forthright with them so they can plan their ­future,’’ Cefalo said.

That process is starting now, said Gerry Cupp, owner of Cupp & Cupp Corp. and a longtime vendor in the exchange. With real estate prices surging across Boston, finding good warehouse space close to the city’s core — and to its customers — won’t be easy, Cupp acknowledged. But he was hopeful.

“We’re trying to get organized and get another building together,’’ he said. “We’ve located a couple of ­possibilities and we’re trying to sort out financing.’’

First though, the flower vendors have a big holiday to get through.

“Valentine’s Day is a big deal around here,’’ Cupp said. “After that, hopefully we can get down to ­business.’’

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.