One grows flowers (6)
I believe the answer is:
irises
'flowers' is the definition.
(type of flower)
'one grows' is the wordplay.
'one' becomes 'i' (Roman numeral).
'grows' becomes 'rises' (rise can mean to grow or increase).
'i'+'rises'='IRISES'
(Other definitions for irises that I've seen before include "Flags" , "Is sire in favour of flowers?" , "Plants with sword-shaped leaves" , "Eye membranes or showy flowers." , "Parts of eyes or flowering plants" .)