Tree died following onset of blizzard — tree in which you'll find rot (10)
I believe the answer is:
balderdash
'rot' is the definition.
(I've seen this before)
'tree died following onset of blizzard tree' is the wordplay.
'tree' becomes 'alder' (alder tree is a kind of tree).
'died' becomes 'd' (abbreviation next to the year of someone's death).
'following' is a charade indicator (letters next to each other).
'onset of' says to take the initial letters.
'tree' becomes 'ash' (ash tree is a kind of tree).
The initial letter of 'blizzard' is 'b'.
'alder'+'d'='alderd'
'alderd' put after 'b' is 'balderd'.
'balderd'+'ash'='BALDERDASH'
'in which you'll find' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for balderdash that I've seen before include "cobblers > GAME" , "Senseless talk/writing" , "Senseless talk" , "bull" , "Bunk" .)