Fixes blame on climbing plant (7)
I believe the answer is:
parsnip
'plant' is the definition.
(parsnip is a kind of plant)
'fixes blame on climbing' is the wordplay.
'fixes' becomes 'pins' (pinning is a kind of fixing).
'blame' becomes 'rap' (synonyms).
'on' means one lot of letters go next to another.
'climbing' shows that the letters should be reversed in order (in a down clue, letters climb up).
'pins'+'rap'='pinsrap'
'pinsrap' reversed gives 'PARSNIP'.
(Other definitions for parsnip that I've seen before include "Type of root veg" , "Tapering vegetable" , "Pale carrot-like vegetable" , "Spar pin (anag) - vegetable" , "Plant with edible white root" .)