Question about trimmer border (8)
I believe the answer is:
hedgerow
'border' is the definition.
(I've seen this before)
'question about trimmer' is the wordplay.
'question' becomes 'how' (I've seen this in other clues).
'about' is an insertion indicator.
'trimmer' becomes 'edger' (I've seen this in another clue).
'how' enclosing 'edger' is 'HEDGEROW'.
(Other definitions for hedgerow that I've seen before include "rural boundary" , "Line of entwined bushes and trees" , "Line of shrubs as barrier" , "Field border" , "Field boundary" .)