Park official that is overwhelmed by huge greenhouses? (10)
I believe the answer is:
orangeries
'greenhouses?' is the definition.
(I know this)
'park official that is overwhelmed by huge' is the wordplay.
'park official' becomes 'ranger' (I've seen this before).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'overwhelmed by' indicates putting letters inside (inserted letters get absorbed or overwhelmed).
'huge' becomes 'os' (abbreviation for outsize).
'ranger'+'ie'='rangerie'
'rangerie' placed into 'os' is 'ORANGERIES'.
(Another definition for orangeries that I've seen is " housing for some mandarins".)