Breaks down seed or mixture (6)
I believe the answer is:
erodes
'breaks down' is the definition.
(I've seen this in another clue)
'seed or mixture' is the wordplay.
'mixture' indicates anagramming the letters.
'seed'+'or'='seedor'
'seedor' anagrammed gives 'ERODES'.
(Other definitions for erodes that I've seen before include "Wears away as by time or water" , "Wears away with weather" , "Eats away" .)