Sow unusual box hedges that flower (7)
I believe the answer is:
cowslip
'flower' is the definition.
(I've seen this before)
'sow unusual box hedges that' is the wordplay.
'unusual' is an anagram indicator.
'box' becomes 'clip' (both can mean to hit someone).
'hedges that' is an insertion indicator (hedge can mean to surround).
'sow' is an anagram of 'ows'.
'ows' going inside 'clip' is 'COWSLIP'.
(Other definitions for cowslip that I've seen before include "Yellow field flower" , "bloomers cover this" , "Wild spring flower" , "Flower related to primrose" , "Yellow flower for unsteady bovine?" .)