Part of flower's trimmed, as in a tangle (9)
I believe the answer is:
midstream
'part of flower's' is the definition.
(part of a river, ie something which flows)
'trimmed as in a tangle' is the wordplay.
'in a tangle' is an anagram indicator.
'trimmed'+'as'='trimmedas'
'trimmedas' with letters rearranged gives 'MIDSTREAM'.
(Other definitions for midstream that I've seen before include "halfway across the water" , "Part-way through a course" , "centre" , "Don't change horses here" , "no place to remount" .)