Producer Kevin Wallace said Wednesday that the $24 million, 3 1/2 hour show will close Sept. 3.
"We're doing respectable but were not sold out. The scale of this show needs that," Wallace said at a news conference.
"The costs are 50 percent more than 'The Lion King' to run so it (the theater) must be full," producer David Mirvishadded.
It was announced last week that "The Lord of the Rings," believed to be the most expensive show ever mounted, will open in London next year -- trimmed, tightened and reworked since its Toronto premiere at the Princess of Wales Theatre in March.
The show's debut met with a harsh critical reception.
The Associated Press said it was "lavish yet disappointing ... a case of imagination overwhelmed by complexity."
The New York Times said, "Everyone and everything winds up lost in this ... adaptation of J. R. R. Tolkien's cult-inspiring trilogy of fantasy novels. That includes plot, character and the patience of most ordinary theatergoers."
The show, based on Tolkien's literary trilogy about a Hobbit named Frodo and his quest to rid Middle-earth of evil, received the financial blessing of the Ontario provincial government, which had contributed $2.5 million. Tolkien's story was adapted by Shaun McKenna and director Matthew Warchus.
Though not considered a musical by its creators, "The Lord of the Rings" has moments of song -- an odd amalgam of sounds by Bollywood master A.R. Rahman and Varttina, a Finnish folk group.
Wallace said that the stronger Canadian dollar and negative reviews from theater critics made American tourists reluctant to come to Toronto to see the show.
The London show will have changes, he said -- they'll give it a "heightened emotional pulse."
Mirvish said that by taking the production to London in September they'll protect some of their investment. There are 17 elevators embedded in a 36-ton, computer-controlled stage floor. Over 50 actors perform in the show.