Land in part of garden that's ruined (8)
I believe the answer is:
blighted
'ruined' is the definition.
(thesaurus)
'land in part of garden' is the wordplay.
'land' becomes 'light' (lighting is a kind of landing**).
'in' is an insertion indicator.
'part of garden' becomes 'bed'.
'light' going within 'bed' is 'BLIGHTED'.
'that's' is the link.
(Other definitions for blighted that I've seen before include "Spoilt, harmed" , "Spoiled, harmed; infected" , "Withered with disease like potatoes in famine" , "Damaged" .)