I don't really do anything special. I do have a bucket of water that I use to fill up watering cans between heavy duty waterings and I mist every time I go in there .. The floor is pebbles with concrete pavers down the middle which I spritz as well. The plants are actually off the floor on what I call my plant decks which helps with air circulation. Also I have a box fan that goes on at around 5pm to 9am to keep the air moving at night. The picture was taken in mid October of last year when I started to load up the GH. One thing though, high humidity with stagnant, unmoving air is not a good thing in my experience. Once I started using the box fan I had less problems with mold, mildew, algae growth and rot.
