Rubbish vegetation left out (5)
I believe the answer is:
pants
'rubbish' is the definition.
(informal term meaning poor-quality)
'vegetation left out' is the wordplay.
'vegetation' becomes 'plants'.
'left' becomes 'L' (common abbreviation).
'out' indicates named letters should be taken away.
'plants' with 'l' removed is 'PANTS'.
(Other definitions for pants that I've seen before include "Rubbish -- underwear" , "Garment; rubbish" , "Breathes heavily in trousers" , "sounds exhausted" , "Briefs" .)