In close up, a poor start is a bit of a bloomer (5)
I believe the answer is:
sepal
'a bit of a bloomer' is the definition.
(part of a flower)
'in close up a poor start' is the wordplay.
'in' indicates putting letters inside.
'close up' becomes 'seal' (I've seen this before).
'start' indicates taking the first letters.
The first letter of 'poor' is 'p'.
'seal' going around 'p' is 'SEPAL'.
'is' is the link.
(Other definitions for sepal that I've seen before include "bit of a bloomer" , "Enclosing part of flower" , "Calyx segment" , "Lapse about part of a flower" , "Part of the calyx of a flower" .)