The high humidity in the room this past winter resulted in the growth of mold on soil and at times on dead plant tissue. I'd like to place a fan in the room to circulate the air. Do I need to put the fan on a timer to turn it on and off on a schedule? Or should control be based on the ambient room temperature? Or do I simply keep it running all the time? In years prior I opened a window and didn't have this problem. I thought the plants would benefit from the extra bit of warmth. What is the proper thing to do?
I dont think that circulating the air will change the situation much, I would think you need a way to evacuate the stale air (moisture laden) and bring in fresh air. or you could invest in a de-humidifier to reduce the moisture.
I disagree. Moving air can cut down on a lot of problems, such as powdery mildew and white fly. Moving air can also even out temperatures in the room. During winter, with homes heated by forced-air nautral gas, I wouldn't think lowering humidity was wise. I also asked my roommate, who works in a community college greenhouse in this area. He says: "All good greenhouses have fans that circulate the air to keep down problems with mold and, more importantly, mildew. Mildew can set in on a plant without airflow in high humidity and warmth. I would run the fan continuously if possible. At the very least during the day when it was warmest. Some plants such as begonias may still get mildew even with air circulation."
The room is unheated with temperatures in the range 10C/50F-20C/68F and RH in the 80s. I should try using a fan next year as an experiment, just to see what would happen.
I believe the air circulation keeps the surfaces of the plant dry even in high humidity, so should help prevent fungus, molds and such.
I have seen pictures of a certain sort of house plant ;) with loads of oscillating fans running. I'll see what i can find out for you. We have a fan in one of our tunnels, it runs 24 hours a day.....so i'd say it would be a good idea, i'll let you know if i find out anything about in high humidity rooms :D