To break a plate is a bit of a bloomer (5)
I believe the answer is:
petal
'is a bit of a bloomer' is the definition.
(I've seen this before)
'to break a plate' is the wordplay.
'to break' indicates anagramming the letters (letters broken up and rearranged).
'plate' with letters rearranged gives 'PETAL'.
(Other definitions for petal that I've seen before include "Part of a plant's perianth that is usually brightly coloured" , "Brightly-coloured part of flower" , "Floral segment" , "part taken from stock?" , "Small seal set in a ring" .)