I don't have M. maculosa but M. virginica and it is native here but is thriving in a raised bed under the eaves of the greenhouse. It receives virtually no moisture and is blooming right now.
The humidity is not an issue here yet we stay in the 80% to 90% humidity at all times in summer.
As a result, I would suspect it is the rain and perhaps some bug that thrives in that same climate.
