Maybe Granny has put out Merlot just for show (10)
I believe the answer is:
ornamental
'just for show' is the definition.
(I've seen this in another clue)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for ornamental that I've seen before include "showy" , "Decorative" , "non-functional" , "Plant grown for attractive appearance" , "Fancy" .)