Horticultural hobby (6)
I believe the answer is:
bonsai
'horticultural hobby' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bonsai that I've seen before include "Japanese shrub" , "Bosnia (anag.)" , "Art of dwarfing shrubs" , "specimen with restricted roots?" , "Japanese craft of growing miniature trees" .)