Answer: Since your blue potato bush grows quickly, you can achieve the treelike form in just a couple of years. Start by identifying a single, vigorous, upright stem and removing any other stems on the plant. Stake the stem straight (if necessary) and remove all of the leaves/branches along the stem, allowing only a few at the very top of the stem. Your plant will need foliage in order to live and grow, so leave 5-8 stems (depending upon its current size) at the top. As the stem grows upward, cut off all but the top 6-8 stems and rub out anything that tries to sprout along the trunk. When your potato bush reaches approximately the height you want it to maintain, begin pinching out the tips of the new growth at the top. This will keep it from growing up too tall and will encourage branching of the stem tips that you pinch, resulting in a topknot of foliage (and flowers).
Best wishes with your project!
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