Visitors to this year's annual Biology Butterfly Show at Carleton University can feast their eyes on a rare sight.

An agave plant is about to have its massive, once-in-a-lifetime bloom.

The plant, called the Queen Victoria agave, has grown significantly in preparation to bloom. It now stands around three metres high, in the corner of the greenhouse where the university's butterfly show is happening this weekend.

The show is at the Nesbitt Biology Building at the southeast end of the university's campus.

The show is free, but donations are accepted.