Sail had been placed over the garden flowers (7)
I believe the answer is:
dahlias
'the garden flowers' is the definition.
'dahlias' can be an answer for 'flowers' (dahlia is a kind of flower). I'm not sure about the 'the garden' bit.
'sail had been placed' is the wordplay.
'been placed' indicates anagramming the letters.
'sail'+'had'='sailhad'
'sailhad' is an anagram of 'DAHLIAS'.
'over' is the link.
Can you help me to learn more?
(Other definitions for dahlias that I've seen before include "'Hid, alas, among the flowers (7)'" , "Flowers for Shia lad" , "Tuberous Mexican flowers" , "I had Al's fowers" , "bloomers" .)