Row about bush's first flower (5)
I believe the answer is:
tiber
'flower' is the definition.
(I've seen this before)
'row about bush's first' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'about' is an insertion indicator.
'bush's first' becomes 'b' (1st letter of 'bush').
'tier' going around 'b' is 'TIBER'.
(Other definitions for tiber that I've seen before include "River entering the Mediterranean at Ostia" , "Italian river with Ostia at its mouth" , "Italian banker" , "Roman river" , "divides Rome" .)