The time when flowers are in full bloom; the state of being fully in bloom.
公園の桜は今まさに花盛りだ。
The cherry trees in the park are right now in full bloom.
春になると町中が花盛りで華やぐ。
When spring comes, the whole town blooms and brightens up.
庭のバラが花盛りなので、毎朝水をやっている。
The roses in the garden are in full bloom, so I water them every morning.
The age or period when someone (especially a woman) is at the peak of their beauty or youth.
彼女は結婚しても花盛りのように若々しい。
Even after getting married, she remains youthful as if at her prime.
学生時代は人生の花盛りとも言える。
Student days can be said to be the prime of life.
あの俳優は今がまさに花盛りだ。
That actor is right now at the peak of his popularity/prime.
A state of booming or peaking (in popularity, business, etc.); flourishing strongly.
観光地はゴールデンウィークで花盛りだ。
The tourist spots are booming during Golden Week.
あの会社は数年前から花盛りで、支店を次々と出している。
That company has been thriving for years and is opening branches one after another.
文化面でも花盛りの時代だった。
It was also a culturally flourishing time.