Common plant (5)
'common plant' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for grass that I've seen before include "Lawn - informer" , "Turf" , "blades" , "Plant used for lawns" , "copper may rely on him?" .)
(Other definitions for hosta that I've seen before include "Ornamental foliage plant; as hot (anag.)" , "Garden plant with ornamental foliage" , "Athos (anag) - perennial plant" , "flowering plant" , "found in a bed, perhaps" .)