Study of gardening? (3)
I believe the answer is:
den
'study' is the definition.
(I've seen this before)
'of gardening?' is the wordplay.
'of' says the answer is hidden in the clue.
'DEN' is hidden within 'gardening'.
(Other definitions for den that I've seen before include "Wild animal's home" , "Animal's lair or gent's study" , "Private office" , "Animal's lair or man's study" , "Cave" .)