Cultivating fruit on top of greenhouse (7)
I believe the answer is:
raising
'cultivating' is the definition.
(raising is a kind of cultivating)
'fruit on top of greenhouse' is the wordplay.
'fruit' becomes 'raisin' (raisin is a kind of fruit).
'on top of greenhouse' becomes 'g' (I am not sure about this - if you are sure you should believe this answer much more).
'raisin'+'g'='RAISING'
Can you help me to learn more?
(Other definitions for raising that I've seen before include "Growing" , "Promoting (in rank)" , "Lifting" , "Bringing up" , "Elevating" .)