Fertilise developing plant with Eastern oil (9)
I believe the answer is:
Here is my best explanation:
'fertilise' is the definition.
(pollinating is a kind of fertilizing)
'developing plant with eastern oil' is the subsidiary indication.
'developing' indicates an anagram.
'with' is a charade indicator (letters next to each other).
'eastern' becomes 'e'.
'plant' put after 'eoil' is 'eoilplant'.
'eoilplant' is an anagram of 'pollinate'.
(Another definition for pollinate that I've seen is "Fertilise (flower)".)