Row with Heather is vexing (8)
I believe the answer is:
rankling
'is vexing' is the definition.
(I've seen this before)
'row with heather' is the wordplay.
'row' becomes 'rank' (I've seen this before).
'with' means one lot of letters go next to another.
'heather' becomes 'ling' ('ling' can be a synonym of 'heather').
'rank'+'ling'='RANKLING'
(Other definitions for rankling that I've seen before include "causing some bitterness" , "causing resentment" , "leaving a nasty taste in one's mouth" , "getting up one's nose" , "annoying" .)