My mums keep dying
I live in Florida and we had a considerable amount of rain previously which led to most of my mums dying, I think. I've only had this batch of mums for about 6 weeks and although they were only around for the tail end of the rains, all the flowers have turned brown. What causes the flowers to turn brown? Do you think it was caused by root rot D/T over watering? How can I keep the flowers longer?
Depending on the age of the plant, the temperatures and sunlight conditions the blooms will fade at different rates.
Keeping the plant dead headed will help encourage more blooms.
Pinching plants back after blooming periods will help with later blooming.
Mums do need well draining soil, so if the roots remain in soggy soil they certainly suffer from root rot.
You would see the entire plant show signs, not just the flowers.
Here are some care links for you.