How to Control Humidity in a Grow Room

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Plants and people require significantly different growth conditions to stay comfortable and remain healthy. Those differences lead serious gardeners with large amounts of indoor plants to design and create specialised grow rooms to house their greenery.

Growing plants need the humidity levels in the air around them to fall between 40 and 75 per cent. While Purdue University recommends clumping plants near one another and placing them in a tray with moist gravel to maintain the necessary humidity, gardeners can use other tactics to maintain better, more measurable control of the humidity in a grow room.

Seal the room as well as possible to prevent outside elements from affecting the humidity in the room. Cover them with the protective plastic sheeting normally used to hold heat indoors in the winter, or install tight weather stripping around the windows and doors.

Control the water sources in the room, as evaporating water can raise humidity quickly. Turn off any sinks, hoses or spigots when you are not using them, and make sure they do not drip. Cover any tanks holding standing water or liquid nutrients. Clean up any liquid spills immediately.

Install a hygrometer, which basically acts like a humidity thermometer. Check the humidity level in the room periodically to ensure the moisture in the air remains at adequate levels.

Turn on a mister or humidifier whenever the hygrometer shows the humidity in the room has dropped below 40 per cent. Run the humidifier until you achieve a 50 to 60 per cent humidity in the room.

Install a ventilation fan, making sure to select a fan rated for the size of the grow room. Run the fan at a low speed to provide air circulation to the room and avoid excess humidity build-up. Increase the speed of the fan and make sure the fan is venting outside rather than blowing into the room if your hygrometer shows excessive humidity levels.