Mountains of nettles picked up (5)
I believe the answer is:
peaks
'mountains' is the definition.
(peak can mean the top of a mountain)
'nettles picked up' is the wordplay.
'nettles' becomes 'piques' (both can mean to annoy).
'picked up' indicates a 'sounds like' (homophone) clue.
'piques' is a homophone of 'PEAKS'.
'of' acts as a link.
(Other definitions for peaks that I've seen before include "Mountain tops" , "Highest points" , "Culminates" .)