Hi, Should I run my dehumidifier constantly? I'm currently in flowering stage and humidity is too high at around 70 plus. I've read somewhere that I should only run it when my lights are off. Is that right?
Higher humidity levels in flower is ok early on while the buds are forming. Most growers will reduce the humidity levels later in flowering especially if growing strains like kushes that have tight dense bud structure to reduce the chance of powdery mildew. Higher humidity can help boost production if it is within the guidelines of a VPD [vapor pressure deficit] chart as referred to by Datidk. You have 2 environmental loads in your grow room. The "sensible load" is the temperature you can measure with a standard thermometer...the other is the "latent load" which is measured with a wet bulb thermometer or some other humidity measuring device. There is a direct relationship between the sensible temperature and humidity levels. Warm air will hold more grains of water per pound of dry air than cold air will. This is the reason when you turn the lights off and the air temperature cools off fast, condensation forms on the plant because the air cools off raising the humidity level FAST! This sets up the perfect environment for powdery mildew to develop. A good example of this is setting a cold drink on a table. Condensation forms on the cold glass because the air cools around the glass and it can not hold the additional moisture any longer. This is the same principle used by your air conditioner to dehumidify your home. Condensate forms on the cold evaporator coil and then drains outside the home reducing the humidity level. Simple...right?!