Sick Dahlias

When I bought this dahlia, it was so beautiful with very large purple flowers but the new buds only grow so much before they turn brown and the petals fall off.  Someone suggested that maybe the soil is too wet and that was my thought, too.  I guess the only thing I can do is let it dry right out and see if that helps.  I just hate it when a plant that was thriving begins to die because that means I'm doing something wrong.