Carefree herbalist removes grass from the borders erratically (6)

I believe the answer is:

blithe

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'carefree' is the definition.
(synonyms)

I don't understand the remainder of the clue.

(Other definitions for blithe that I've seen before include "Uncaring" , "With neither worries nor cares" , "Cheerfully indifferent" , "Careless" , "Shelley: 'Hail to thee . . . . . . spirit! Bird thou never wert'" .)

I've seen this clue in The Irish Times.

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