The most common and most likely answer to this crossword clue is the 5 letter word AVENS
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Buddy explains!

The straight part
We know that "a bloomer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a bloomer = avens.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AVENS mean?
AVENS noun- A plant of the genus Geum, especially Geum urbanum, or herb bennet.
- A plant of the genus Dryas.