Supporter of lupins initially in bloom (8)
I believe the answer is:
follower
'supporter' is the definition.
(I've seen this before)
'of lupins initially in bloom' is the wordplay.
'initially' suggests taking the first letters.
'in' is an insertion indicator.
'bloom' becomes 'flower' (synonyms).
The initial letters of 'of lupins' is 'ol'.
'ol' going into 'flower' is 'FOLLOWER'.
(Other definitions for follower that I've seen before include "Attendant" , "A devotee or a pursuer" , "Supporter" , "A loyal adherent - or a pursuer" , "Disciple" .)