Very rich plant producing wagons and things (7,5)
I believe the answer is:
rolling stock
'wagons and things' is the definition.
'very rich plant' is the wordplay.
'very rich' becomes 'rolling'.
'plant' becomes 'stock' (**).
'rolling'+'stock'='ROLLING-STOCK'
'producing' is the link.
(Other definitions for rolling stock that I've seen before include "Locomotives and coaches" , "Railway wagons" , "Rail vehicles" , "Railway vehicles" , "Locomotives, carriages etc" .)