Never agree to give up a hybrid plant (9)
I believe the answer is:
evergreen
'plant' is the definition.
(evergreen is a kind of plant)
'never agree to give up a hybrid' is the wordplay.
'to give up' indicates named letters should be taken away.
'hybrid' indicates anagramming the letters (a hybrid is a mixture).
'never'+'agree'='neveragree'
'neveragree' with 'a' taken away is 'nevergree'.
'nevergree' is an anagram of 'EVERGREEN'.
(Other definitions for evergreen that I've seen before include "Of lasting popularity" , "Enduringly fresh" , "Not all shrubs are" , "Fresh and vital" , "Source of wood" .)