Plant on a grimy ground (8)
I believe the answer is:
agrimony
'plant' is the definition.
(agrimony is a kind of plant)
'on a grimy ground' is the wordplay.
'ground' indicates anagramming the letters (grind the letters ).
'on'+'a'+'grimy'='onagrimy'
'onagrimy' with letters rearranged gives 'AGRIMONY'.
(Other definitions for agrimony that I've seen before include "Growth" , "Plant with yellow flower-spikes" .)