As I mention in my article on this topic at Interesting Thing of the Day, there are some plants that bloom so rarely that the appearance of their flowers is heralded as a major event. One such plant, the Titan Arum lily, draws huge crowds to botanical gardens whenever one is about ready to bloom; people come to see the enormous spike of flowers it produces, as well as to experience the foul smell it gives off to attract would-be pollinators. Here are a few other plants that take their time when it comes to blooming.
- Night-blooming Cereus cactus [1]—blooms for one night every year
- Titan Arum lily [2]—seldom blooms in the wild, even less frequently when in cultivation (on average every 4-10 years)
- Kurinji plant [3]—blooms every 12 years
- Certain species of bamboo (e.g., Bambusa tulda [4] and Melocana bachiphera [5])—bloom every 40 to 50 years
- Talipot palm [6]—blooms once in its 30–80 year lifespan
Go ahead. Make our day. 
