How do you pronounce 盛开?
You can guess the pronunciation according to its usage:

"盛("chéng")" in 盛饭 is used as a verb, which means to fill or to contain.

"盛("shèng")" in 盛开 is used as a non-verb(adj./adv./noun), which means prosperous(ly), flourishing(ly)... (盛宴,盛装,旺盛,兴盛...)


by the way, 盛"shèng" is also used as a surname, such as this man