In short, flowers make honey.

Literal

Essentially, flower [subject-が] honey [object-を] make-[explanatory-のだ].

Note が marks 花 — this が focuses on 'flowers specifically' as the producer. はちみつ ('honey,' 蜂蜜) is often written in kana for readability. A slightly oversimplified scientific claim (technically bees make honey from nectar, not flowers directly).