Help with my plant!?

i have an indoor pot of yellow dahlias, and there are two problems i need to figure out:

1)why do the flowers grow and then die/dry out so quickly??

2)what are the white splotches of white powdery stuff on the leaves? is that bad, how can i fix that?

i water them enough(the dirt is always moist), and today i let them sit outside in the sun thinking that might help(it didnt).thanks so much!!!!!!

Help with my plant!?
Simply put, you're over-watering. "Soil is always moist" is not a good thing. You must let your plants dry out before watering again. The powder is just that: Powdery Mildew. Without using a fungicide, the best thing you can do is let the soil dry.