Well, MG soil + worm castings = a very water retentive soil - especially if you used the moisture control type. Soils that hold too much water hold too little air.

I would push a wick into the drain hole & allow it to hang below the bottom of the container a couple of inches. That will help to remove any offending perched water (explained here) from the saturated layer of soil at the bottom of the container. After the wick is in place, only water when the wick is dry where it emerges from the pot. When you NEED the additional water the soil is holding to sustain your plants between irrigations, remove the wick. It turns a heavy soil into a dual-purpose soil. ;o)

Remove & destroy the diseased leaves - do not compost. Do not wet the foliage when you water. Also - are you sure that soil temperatures are not climbing too high & weakening the plant, making it more susceptible to myriad maladies (notice the alliteration?). ;o)

If you used any significant volume of worm castings, you may wish to consider leaving them out next time (there are better ways of supplying micronutrients in container culture)- and even adding some pine or fir bark and perlite to the soil to lighten it up. Your benefit will be healthier plants at the expense of having to water a little more frequently.

Al

Hi,
I thought my husband might have been watering too much.We have never had a dwarf sunflower before,so I wasn't sure how much we should water.I didn't know the worm castings would help hold water.thank you for the reply!
Denah