In disarray when horticultural centre's behind (5)
I believe the answer is:
askew
'in disarray' is the definition.
Both the answer and definition are adjectives. Maybe they are linked in a way I don't understand?
'when horticultural centre's behind' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'horticultural centre's behind' becomes 'kew' (I can't justify this - if you can you should believe this answer much more).
'as'+'kew'='ASKEW'
Can you help me to learn more?
(Other definitions for askew that I've seen before include "Wonky" , "Off-centre" , "Oblique" , "irregular" , "Wakes (anag)" .)