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