Gardener's nemesis (4)
I believe the answer is:
weed
'gardener's nemesis' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for weed that I've seen before include "Ineffectual person" , "Uncultivated plant" , "Cannabis; feeble person" , "Hoe to remove it" , "Intrusive plant; weak person" .)