Duck upset about erect garden plant (5)
I believe the answer is:
lupin
'garden plant' is the definition.
(I've seen this before)
'duck upset about erect' is the wordplay.
'duck' becomes 'nil' (both can mean zero).
'upset' shows that the letters should be reversed in order.
'about' indicates putting letters inside.
'erect' becomes 'up'.
'nil' backwards is 'lin'.
'lin' placed around 'up' is 'LUPIN'.
(Other definitions for lupin that I've seen before include "Plant called after wolf" , "Fodder plant" , "Pea relative with tall spikes of flowers" , "Flower with spike of usually purplish-blue flowers" , "Garden plant of the pea family" .)