Possible Clues:

• Japanese method of cultivating miniature trees
• (Cultivation of) dwarf trees
• Dwarf tree cultivation
• Professor Schumacher's favourite tree?
• Japanese art that may produce a little ash?
• Dwarf (tree)
• Oban is fashionable for minimalist art
• Japanese craft of growing miniature trees
• Growing trees for a stunt makes one a snob? Just the reverse!
• Trees having no great variety