Cover on the bed? (7)
I believe the answer is:
topsoil
'cover on the bed?' is the definition.
(soil that covers a flower bed)
'cover on the bed?' is the wordplay.
'cover' becomes 'top' (topping is a kind of covering).
'on the bed?' becomes 'soil' (I can't explain this - if you can you should believe this answer much more).
'top'+'soil'='TOPSOIL'
Can you help me to learn more?
(Other definitions for topsoil that I've seen before include "Garden's surface layer" , "where grass grows" , "Earth's surface" , "The Good Earth" , "Visible layer of garden" .)