The art of growing ornamental dwarfed plants (6)
I believe the answer is:
bonsai
'the art of growing ornamental dwarfed plants' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for bonsai that I've seen before include "Art of dwarfing trees" , "Dwarf tree cultivation" , "specimen with restricted roots?" , "Japanese art of growing dwarfed trees" , "Mini-tree growing" .)