Temperature, humidity and carbon dioxide (CO2) levels are key factors to monitor and control in any indoor garden. But don’t make the mistake of thinking about them separately! In order to really understand how your indoor garden environment works, you need to consider how these factors work together. The best way to do this is to take a look from a plant’s perspective...
Growers use ventilation and cooling during the day and sometimes heaters during the night to manage their temperature differential. TDiffs larger than 18°F (10 °C) should be avoided as this can cause undue stress and impede growth.
How are Temperature and Relative Humidity Connected?
Humidity refers to the amount of water vapor in the air. But the higher the air temperature, the more water vapor air can hold. The term “relative humidity” links the two together (and also factors in air pressure) and is expressed as a simple percentage. A relative humidity of 100% means the air is carrying the maximum possible water vapor for a given temperature. 50% means it’s “half full,” etc.
So what do these percentages mean for your plants? Well, if humidity levels are too low (often caused by too much extraction, high light intensity and arid conditions outdoors) this can cause excessive water loss, desiccation (drying), poor growth and narrow, small leaves.
High relative humidity is usually caused by inadequate ventilation, often symptomatic of local climatic conditions (esp. on the east coast of the US) and results in little or no transpiration, fungal diseases, and very wide or large leaves.
Low relative humidity occurs when there is no available moisture for the air to carry. In warm, plastic lined, heavily ventilated grow rooms there is often no available moisture other than what is being drawn into the grow room, and the moisture transpired by the plants. Many warm grow rooms suffer with low relative humidity problems. Pests like red spider mite love hot, dry grow rooms!