Hedging material in line daily becoming wilder (9)
I believe the answer is:
leylandii
'hedging material' is the definition.
(Leyland cypresses or Leylandii are used for hedges)
'line daily becoming wilder' is the wordplay.
'becoming wilder' is an anagram indicator.
'line'+'daily'='linedaily'
'linedaily' anagrammed gives 'LEYLANDII'.
'in' is the link.
(Other definitions for leylandii that I've seen before include "(Very) fast-growing conifer(s)" , "Tree -- fast-growing conifer" , "Fast-growing plant" , "Fast-growing cypress" , "Evergreen" .)