Grafting receiver, Eliot's taken to cold castle walls (9)
I believe the answer is:
rootstock
'grafting receiver' is the definition.
(plant which another plant is grafted onto)
'eliot's taken to cold castle walls' is the wordplay.
'eliot' becomes 'ts' (TS Eliot).
'taken' is a charade indicator (letters next to each other).
'cold' becomes 'c' (eg on taps).
'castle' becomes 'rook' ('rook' can be a synonym of 'castle').
'walls' means one lot of letters goes inside another (to 'wall' can mean to contain).
'ts'+'to'+'c'='tstoc'
'tstoc' placed within 'rook' is 'ROOTSTOCK'.
(Other definitions for rootstock that I've seen before include "that extends underground" , "Source" , "Rhizome" .)