Possible Clues:

• The art of growing dwarf ornamental trees
• Little tree from free Bosnia
• Vulgar ______ cultivation = outrageous labour-saving?
• Dwarf plant
• Very little tree
• One's a pretentious type about specialist arboriculture
• A snob climbing a first class sort of tree
• Literally, 'tray gardening'
• Often-trimmed tree
• Elitist returned with excellent Oriental art