Plant in estate well clear of borders (9)
I believe the answer is:
groundsel
'plant' is the definition.
(groundsel is a kind of plant)
'estate well clear of borders' is the wordplay.
'estate' becomes 'grounds' (grounds is a kind of estate).
'clear of borders' means to look at the middle letters (the letters which border the word are removed).
The middle of 'well' is 'el'.
'grounds'+'el'='GROUNDSEL'
'in' acts as a link.
(Other definitions for groundsel that I've seen before include "feed to the birds" , "plant, unwanted?" , "Plant of daisy family" , "Common weed" .)