They chop each stem roughly (8)
I believe the answer is:
machetes
'they chop' is the definition.
'each stem roughly' is the wordplay.
'roughly' indicates an anagram.
'each'+'stem'='eachstem'
'eachstem' with letters rearranged gives 'MACHETES'.
(Other definitions for machetes that I've seen before include "Broad heavy knives used as weapons" , "Large heavy knife, weapon or vegetation cutter" , "Teaches M. to use large knives" , "pointed weapons" , "Cheats me with large jungle knives" .)