A bloomer very nearly useless (7)

I believe the answer is:

vervain

'a bloomer' is the definition.
(I know that vervain is a type of bloomer)

'very nearly useless' is the wordplay.
'nearly' means to remove the last letter.
'useless' becomes 'vain' (I've seen this before).
'very' with its last letter removed is 'ver'.
'ver'+'vain'='VERVAIN'

(Another definition for vervain that I've seen is " Plant".)

I've seen this clue in The Daily Express.

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