In autumn it requires gunpowder ingredient (5)
I believe the answer is:
nitre
'gunpowder ingredient' is the definition.
(I've seen this in another clue)
'in autumn it requires' is the wordplay.
'in' indicates the answer is hidden within the clue.
'NITRE' can be found hidden inside 'autumn it requires'.
(Other definitions for nitre that I've seen before include "what goes into bangers" , "Also known as salt-petre" , "explosive component" , "safeguard against decay" , "Salt" .)