Flower close to garden behind (6)
I believe the answer is:
astern
'behind' is the definition.
(at the back or behind of a ship)
'flower close to garden' is the wordplay.
'flower' becomes 'aster ' (type of flower).
'close to' says to take the final letters (the 'close' to the word).
The last letter of 'garden' is 'n'.
'aster'+'n'='ASTERN'
(Other definitions for astern that I've seen before include "Aft" , "Rearward" , "Behind (a boat)" , "Backward" , "Towards back of boat" .)