Better blooming perform! (5)
I believe the answer is:
outdo
'better' is the definition.
(to outdo is to beat or do better than)
'blooming perform' is the wordplay.
'blooming' becomes 'out' (plants which have bloomed are 'out').
'perform' becomes 'do' (both can mean complete an action).
'out'+'do'='OUTDO'
(Other definitions for outdo that I've seen before include "Exceed" , "Overtake" , "going to top?" , "Perform better than (someone)" , "Cap" .)