Full sun is a must- my marginal ones get about 4 hours plus a little late afternoon sun for an hour. Most of them get 6-8 hours a day. Your soil sounds good. If you leave them in the ground in zone 5 without winter protection they might be mush, but then you'd have no growth whatsoever, so that makes no sense. Fertilizer is good, I use Osmocote for ease. Others don't use any at all. Water once or twice a week, depending on rainfall. Don't want them too wet, especially when under a foot tall. Plant tubers about 4-6 inches deep, but again I'd mulch heavily in late Fall to protect from Winter freezing in your climate. An open stalk is a funnel to invite rains down into the tuber clump and rot it. Cover it up with something or wrap it in foil, or cut it off. Better yet, I'd dig up the tubers, divide them, store them and get more plants for yourself or trading.

Did you fertilize with anything that might be burning your leaves? When I had a couple container type dahlias, I recall that they were the first to go as far as blooming went. Those are the only things I can think of for what you describe. I'd just take the brown leaves off, they're not coming back to green, I don't think. Maybe your plant is taking a breather and will have a second spurt?

Hi jordanmichelle, I agree that the photos look like a bad case of Powdery Mildew. " I'm really confused how it got this powdery mildew. I water only at the base and live in a very hot and dry climate. We're experiencing a drought and it's been in at least the 90s throughout the night the past month and well over 100 during the day. " Whenever the subject of Powdery Mildew comes up, someone usually suggests wet foliage as a possibly causative factor. It is a popular misconception that water on foliage promotes Powdery Mildew. The truth is the opposite -- water on foliage can actually fight Powdery Mildew. Powdery Mildew thrives on dry foliage, and when it cools at night it gets the cool dry conditions that favor it. By watering only at the base you were following the advice of those who identify wet foliage as a cause of PM. Unfortunately, they are wrong. Some foliage diseases are favored by wet foliage, but Powdery Mildew is not one of them. ZM

I was thinking the same thing. They spread fast. Take off all the damaged leaves and throw them in your garbage (not compost) before spraying Neem. You can try hand washing with soapy water before spraying, too... Neem doesn't always work for mites. Just stay away from Sevin, as that will make the problem worse! Good luck.