A giant asparagus-like stalk with buds reminiscent of broccoli has sprouted through the greenhouse roof at Allan Gardens Conservatory, majestically bursting almost two meters above the glass toward the sky.

After some 75 years of storing up energy, the agave americana will, finally, for the first time in its life, flower within the next few weeks, producing spectacular yellow blossoms. And then it will die.

This towering plant gives new meaning to the term late-bloomer. It has sat in the conservatory not doing much for likely as long as 50 years, says Curtis Evoy, Allan Gardens superintendent. Members of the Toronto Cactus and Succulent Club have estimated the plant’s age at about 75 years old.

“That’s a plausible estimate, given your cold climate which would slow it down,” says Mary Irish, a Texas horticulturist who specializes in drought-adapted plants. The agave americana, a species originally from Mexico, got its nickname the “century plant” because it was brought to England and Germany, where it took a very long time to bloom, she explains. In the American southwest, it blossoms in a mere 30 years.

In March, gardeners at the Toronto conservatory, on Carlton St. between Jarvis and Sherbourne, first noticed a shoot starting at the plant’s centre. After that, it took off like Jack’s beanstalk. “It happened so fast, you could almost see it growing,” says horticulturist Evoy.

When it hit the glass ceiling, the super-charged stalk started to bend and the conservatory faced a dilemma. The plant would surely die unless they cut the glass, but the outside temperatures in March were hardly tropical. They took the gamble and made a hole big enough for the stalk to poke through. “Luckily it was just warm enough out,” says Evoy. In his 23 years with Allan Gardens, the conservatory has never before had to break the glass ceiling for a plant.

The stalk is now about 4.5 metres (15 feet) tall from base to towering buds. In another two to four weeks, the plant’s yellow flowers should bloom, he says.

And when it does, grab your camera. “There will be hundreds and hundreds of flowers opening in sequence from the bottom up, spreading out on candelabra-like arms and attracting an enormous number of birds and bees,” predicts Irish, plant production manager at the San Antonio Botanical Garden. “It’s quite the spectacle in the plant kingdom.”

All these years, the succulent plant has been gathering energy to be marshaled into the buds, poetic in its one final flourish. “That’s why it dies. It puts everything it has into the flowers,” explains Irish. “It’s a one-shot deal.”

Evoy expects the blooms to last about four to six weeks. Then the plant will shrivel up and turn brown and the stalk will be sawed off.

Presently, though, the odd-looking stalk shooting through the glass can best be viewed from the Carlton Street side of the gardens. “Holy s---, it went right through the greenhouse. Wow,” exclaimed one passerby.