Strongly urge to take part in complex horticulture (6)
I believe the answer is:
exhort
'strongly urge' is the definition.
(I've seen this in another clue)
'part in complex horticulture' is the wordplay.
'part in' indicates a hidden word.
'EXHORT' can be found hidden inside 'complex horticulture'.
'to take' is the link.
(Other definitions for exhort that I've seen before include "Spur on" , "Strongly encourage (someone to action)" , "Strongly urge (someone to do something)" , "Give great encouragement to" , "Urge, advise earnestly" .)