Flower college planted in a mixture of peat (7)
I believe the answer is:
petunia
'flower' is the definition.
(petunia is a kind of flower)
'college planted in a mixture of peat' is the wordplay.
'college' becomes 'uni' (I've seen this in other clues).
'planted in' is an insertion indicator.
'a mixture of' is an anagram indicator (I've seen this in other clues).
'peat' with letters rearranged gives 'peta'.
'uni' put inside 'peta' is 'PETUNIA'.
(Other definitions for petunia that I've seen before include "Common bedding plant" , "Flowering plant" , "Auntie foolishly made under pressure" , "Plant related to tobacco" , "Plant cultivated for its white, pink, blue or purple funnel-shaped flowers" .)