Answer: It's true, there is such a thing as too much information. First hand experience is a great teacher for willing students, too! For instance, pinching back is recommended for SHORT varieties of dahlia, but large ones should be allowed to grow as tall as they want, and often cages or stakes, as you mentioned. You may have removed the majority of growing points from your plants, so they won't really thrive this year. If they lack leaves, they aren't storing nutrients in the tuber for better growth next year, and may simiply be drawing from stored food to grow this year. When you lift the tubers this fall, see if they have grown or shrunk. You may want to start with new tubers next spring.
You probably also read that they need a deep, rich, humusy soil, full sun and lots of air circulation for best growth. They prefer to be watered only when it's droughty, and only about once a week after bloom begins. I wonder about the fertility and/or pH of your soil. A pH that's out of their preferred range (6-7.5) will lock up essential nutrients and result in stunted growth. Bonemeal applied to the soil in June and early August encourages good root growth and enlargement of the tubers. What you can do now is make sure these conditions are met, and prepare for next year's planting. Hope this helps!
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