Dehumidifiers for cannabis are a good thing to invest in as marijuana is very sensitive to humidity. Having too much humidity is associated with such diseases as alternaria, botrytis, and downy mildew. The most effective way to avoid these and eradicate diseases is to treat your grow room with a dehumidifier, this will also stimulate the growth and grow quality of your yield, increasing the overall dry weight mass.
You require a dehumidifier as plants always are transpiring water, thus causing humidity levels to soar. If this situation goes on for a long time unchecked, the relative humidity can reach 100% very soon. If the air is this saturated with water vapour, then the dew point is arrived at and water will begin to condense on cooler surfaces, this will include the inside of the buds and on the plant. It is so important to avoid this as this will cause disease outbreaks and pathogens to develop. Try to do this without chemicals due to the strict cannabis regulations as well as it is not preferable for commercial and medical use. This is why you should start with dehumidification.
With so many options for humidity control that is on the market, it can be hard to source the one that you require. Most have traditional purposes in mind when they are designed, such as for storage or industrial processes- this is not the best for the specific conditions that are found in a grow room.
Because of cultivation purposes, find a humidifier designed for grow conditions. The benefit of using a unit specifically made to get water out of the air at conditions best for marijuana (which is around 64 degrees Fahrenheit and a 60-80% RH) is that there is optimal humidity reduction. One may think that using HVAC cooling systems or fans would be an efficient method to reduce the humidity of a grow room, but these are not sufficient enough. It is true that these systems are useful at reducing humidity, but this is merely the byproduct of their operation and is not the same as having an optimized or specific-to-the-job condensation system.