Concerning smell made by trimming elderly plant (9)

I believe the answer is:

olfactory

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'concerning smell made by trimming' is the definition.
I can't judge whether this definition defines the answer.

'elderly plant' is the wordplay.
'elderly' becomes 'ol' (I can't explain this - if you can you should give a lot more credence to this answer).
'plant' becomes 'factory'.
'ol'+'factory'='OLFACTORY'

Can you help me to learn more?

(Other definitions for olfactory that I've seen before include "Pertaining to the sense of smell" , "Smelling" , "concerned with smell" , "Dealing with smells" , "Detecting scent" .)

I've seen this clue in The Times.

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