Iron, sulphur, copper, oriental grass (6)
I believe the answer is:
fescue
'grass' is the definition.
(I've seen this before)
'iron sulphur copper oriental' is the wordplay.
'iron' becomes 'Fe' (Fe is the chemical symbol for iron).
'sulphur' becomes 'S' (synonyms).
'copper' becomes 'cu' (chemical symbol).
'oriental' becomes 'e'.
'fe'+'s'+'cu'+'e'='FESCUE'
(Other definitions for fescue that I've seen before include "It might be part of green" , "Pasture grass featured on putting greens" , "A fine pasture grass" , "Type of pasture grass" , "Pasture grass often found on golf course putting greens" .)