English flower festival (6)
I believe the answer is:
easter
'festival' is the definition.
(I've seen this before)
'english flower' is the wordplay.
'english' becomes 'e' (abbreviation).
'flower' becomes 'aster' (aster is a kind of flower).
'e'+'aster'='EASTER'
(Other definitions for easter that I've seen before include "Major Christian festival in April" , "Parade; egg; lily" , "Teaser about Christian festival" , "Christian celebration for Teresa" , "Christian festival in Spring" .)