Eighteen inches of top growth on what? Growth regulators don't enhance growth, btw, they supress it.

Mainly my question is pointed at japanese maples, as well as several types of native michigan trees and shrubs.
(I am aware of the growth regulators which supress top growth in favor of a more vigorous root system, i was wondering if there was also some that promote it.)

Thanks for elaborating on your question, it helps define answers. I do some woody stock in my business, but it's not my major line so there should be somebody who can answer your question better than I. I am not aware of any growth regulators to promote growth in the strictest sense of growth regulators. I should think that growth would be linked more to proper environment, nutrition and irrigation. You may want to ask this question on the tree forum. There are some pros there who deal mostly with trees and very many really knowledgeable hobbyists. Good luck.

Container grown woody plants require a very porous, bark-based potting medium, plenty of good light, the proper amount of fertilizer, and lots of watering. The more porous your medium, the more often you can water. Fresh, oxygenated water flow though the container mix greatly enhances growth and development.