Certified GKH Gardening Expert
I'm seeing a sign of infection! Watering at night, and overwatering are likely the cause.
The best time to water will be early morning, so that the soil does not remain wet, as it will watering at night. Moist is fine, but wet conditions promote rot outside of woodland settings.
It is also necessary to let the soil dry, some, down to about an inch, but not completely dry between waterings. This will vary in time, depending on environmental conditions at the time. Watering on schedule will not work, as the moisture content will need to be checked between watering. The watering care for these plants is not, exactly, straighforward.
The next thing to look at will be nitrogen content. If you have fed the area with anything high in nitrogen, or used bird manures high in urea, then this will cause large leaves and less than par flowers.
Be sure to test soil before adding fertilizers to know what it needs.
Soil pH can have an affect as well.
Here are some articles that will help: