1
flowers in full bloom;time of year in which flowers are in full bloom
庭のバラは今花盛りです。
The roses in the garden are in full bloom.
2
the age at which someone (esp. a woman) is at the peak of their beauty
3
booming or peaking (in popularity)
詩人としての彼は20代が花盛りだった。
As a poet, he flowered in his twenties.
Other forms
花ざかり 【はなざかり】