Unwanted vegetation (5)
I believe the answer is:
weeds
'unwanted vegetation' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for weeds that I've seen before include "Unwanted plants" , "mourning clothes" , "Are they worn by widows in the garden?" , "Black garments once worn by widows" , "Wild plants; mourning garb" .)