Unwanted plant in a garden (4)
I believe the answer is:
weed
'unwanted plant in a garden' 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 "Troublesome plant" , "dope" , "Work in garden" , "Plant growing where it is not wanted" , "Uncultivated plant" .)