Plant a gentile cultivated with nitrogen (9)
I believe the answer is:
eglantine
'plant' is the definition.
The answer is an example.
'a gentile cultivated with nitrogen' is the wordplay.
'cultivated with' is an anagram indicator.
'nitrogen' becomes 'N' (N is the chemical symbol for nitrogen).
'a'+'gentile'='agentile'
'agentile' with its letters mixed up with 'n' makes 'EGLANTINE'.
(Other definitions for eglantine that I've seen before include "Inelegant (anag) - plant" , "Rose, growing wild" , "Milton's honeysuckle" , "Sweetbriar, inelegant in a way" , "Strangely inelegant scented plant" .)