As he redesigned first flower border here? (5,3)

I believe the answer is:

irish sea

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'border here?' is the definition.
The definition suggests a singular noun which matches the answer.

'as he redesigned first flower' is the wordplay.
'redesigned' indicates anagramming the letters.
'first' means one lot of letters go next to another.
'flower' becomes 'iris' (I've seen this before).
'as'+'he'='ashe'
'ashe' anagrammed gives 'hsea'.
'hsea' put after 'iris' is 'IRISH SEA'.

Can you help me to learn more?

(Other definitions for irish sea that I've seen before include "Water around Isle of Man" , "Main" , "Waters separating Ireland from England and Wales" , "It separates Ireland from Britain" , "Man's situation" .)

I've seen this clue in The Guardian.

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