Flower getting large in period of prosperity (5)
I believe the answer is:
bloom
'flower' is the definition.
(I know that flower can be written as bloom)
'large in period of prosperity' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'in' is an insertion indicator.
'period of prosperity' becomes 'boom' (I've seen this before).
'l' placed into 'boom' is 'BLOOM'.
'getting' is the link.
(Other definitions for bloom that I've seen before include "Blossom, flower" , "Coat (lens); flower" , "Do very well" , "Flush" , "look good" .)