Flower in my control (7)
I believe the answer is:
mastery
'control' is the definition.
(mastery can mean control or command of something)
'flower in my' is the wordplay.
'flower' becomes 'aster' (type of flower).
'in' means one lot of letters goes inside another.
'aster' put within 'my' is 'MASTERY'.
(Other definitions for mastery that I've seen before include "in full command" , "Expert skill" , "Supremacy" , "Total control" , "superior knowledge" .)