CACTUS plants are among the slowest-growing plants and one kind, the saguaro, grows only 2,5cm over the first 10 years of its life.
The plant grows its first branch when it is 16 years old and after that it grows 2,5cm a year. The cactus only starts to flower when it is about 60 years old.
This is slow, but some pine trees found in the cold Arctic or high up on a mountain grow even slower. A Sitka spruce in the Arctic, for example, grew 28cm in 98 years! - bigsiteofamazingfacts.com; wikipedia.org; angelfire.com