Vapor Pressure Deficit (VPD) is a measurement of the difference between the amount of moisture in the air and the amount of moisture that the air can hold when it is saturated. In short, VPD is the difference between the actual vapor pressure (VP) and the saturation vapor pressure (SVP) of the air.
In cannabis growing, VPD plays a crucial role in the overall growth and development of the plant. VPD affects the transpiration rate of the plant, which is the process by which plants take in water through their roots and release it into the atmosphere through small pores on their leaves called stomata.
Measuring VPD
There are many tools that can be used to measure VPD in a cannabis grow room. The most common tool is a digital hygrometer, which measures both temperature and humidity. With these measurements, it is possible to calculate the VPD using an online VPD calculator or a chart.
Another tool that can be used to measure VPD is a thermal hygrometer. This tool measures both the temperature and humidity and displays the VPD directly on the screen.
Adjusting VPD
There are several ways to adjust VPD in a cannabis grow room. One of the most effective ways is to adjust the temperature and humidity levels. By increasing or decreasing the temperature and humidity, it is possible to change the VPD.
Another way to adjust VPD is to adjust the amount of water that is being supplied to the plants. By increasing or decreasing the amount of water, it is possible to change the transpiration rate of the plant, which in turn affects the VPD.
It is important to note that VPD should be adjusted gradually to avoid stressing the plants. Growers should also be aware that different strains of cannabis may have different ideal VPD ranges, and adjustments may need to be made accordingly. By regularly monitoring and adjusting VPD, growers can ensure healthy and robust cannabis plants with high yields and potency.
VPD is too low
When the VPD is too low, the moisture in the air is too high, and the plant's transpiration rate slows down. This can lead to the development of mold and other fungal diseases, as well as stunted growth due to lack of oxygen.
VPD is too high
On the other hand, when the VPD is too high, the moisture in the air is too low, and the plant can become dehydrated. This can cause the leaves to wilt and curl, and can also lead to stunted growth due to lack of water.
Ideal VPD
To achieve the ideal VPD for cannabis growing, it is recommended to maintain a VPD range of 0.8 to 1.3 kPa during the vegetative stage, and a range of 1.3 to 1.8 kPa during the flowering stage.
VPD by Stage
Vegetative
Maintaining the proper humidity and temperature levels during the vegetative stage is crucial for healthy growth. Aim for a humidity level of around 50-70% and a temperature range of 70-85°F (21-29°C). High humidity levels can lead to mold and mildew growth, while low humidity levels can cause your plants to dry out and stress. Keeping the temperature within the optimal range can also help prevent pests and diseases from taking hold.