Grass to spare (7)

I believe the answer is:

esparto

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'grass' is the definition.
(type of grass plant)

'to spare' is the wordplay.
'to spare' can be anagrammed to 'ESPARTO'.
However, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for esparto that I've seen before include "Coarse type of grass" , "Grass, used for ropes, paper" , "Tough, coarse grass" , "Grass fibre for mat-making" , "A poster (anag.)" .)

I've seen this clue in The Irish News.

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