Tree-dwarfing art (6)
I believe the answer is:
bonsai
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">tree-dwarfing art</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for bonsai that I've seen before include "Art of dwarfing shrubs" , "Little plants" , "Mini-tree growing" , "Dwarfed ornamental tree or shrub" , "The art of growing ornamental dwarfed plants" .)