Vapor-Pressure Deficit (VPD) in Cannabis

What is Vapor Pressure Deficit (VPD): 

Definition: 

Vapor-Pressure Deficit/Differential (VPD) is defined as the difference/deficit between the amount of moisture in air and the maximum moisture the air can withhold when it is fully saturated. As soon as the air gets saturated, water condenses to form clouds, dew drops or thin film of water over leaves. 

Why (VPD) is important: 

The successful growth of Cannabis and the subsequent obtaining of high yield with top quality flowers are considerably dependent upon two important climatic factors such as Temperature and Relative Humidity, especially in the protected environment, where artificial lightening system is efficiently managed to get the targeted outcome. Vapor Pressure Deficit (VPD) relates with both of the above mentioned growing factors which defines the amount of water vapors that the atmosphere can retain (depends on temperature) and the amount of water vapors contained in it (Relative Humidity), thus measuring in Kilo Pascal (kPa).  

VPD greatly effects on several processes occurring in the plant body such as transpiration and nutrient uptake. In order to help your plant to intake maximum amount of nutrient from growing medium, CO2 from air and for the leaf’s pores or stomata “breathe” out oxygen you will have to control your environment to make the best conditions for your plant to grow and become stronger.  

The best way to have your perfect VPD would be with environmental controller which can automatically keep your desired VPD during the day. Keep in mind that keeping your VPD in desired range the best practice shows that it needs to be done with automated environmental controller. This is because VPD consist of 2 values temperature and humidity and you need to control both in order to get to your desired range of VPD. (the green range is the best) 

Therefore, the ideal adjustment of Temperature and humidity determines the best possible VPD value (as shown in the chart) which can maximize the development of cannabis plants. Data shows that at lower temperature (15°C) and less humidity (40-55%), VPD value has to be maintained between 7.6-10.2 kPa, while by increasing temperature(34°C) and relative humidity (85%), optimum value of VPD is 8 kPa. This clearly shows that the VPD Chart in relation to Temperature and Humidity in Cannabis cultivation (green, orange and red zones) must follow for optimum results. If the value of VPD is between  5-12 kPa, cannabis plants open stomata thus higher transpiration from leaves to air occurs, which increases the efficacy of photosynthetic activities and is an indication of requiring more nutrients to apply during growth and bloom. The best range of VPD is recorded between 7.5-10.5 kPa, falling in green zone. Low level of VPD combined with high relative humidity may cause nutrient deficiency, weak growth and inviting the plant to a number of diseases (wilting, curl or crisp leaves).  

VPD in Cannabis: 

  • Vapor Pressure is the pressure at which liquid becomes a vapor. In Cannabis Cultivation, VPD refers to the difference between the vapor pressure within the plant and the vapor pressure of the surrounding of the plant. VPD drives transpiration. And upon transpiration, the plant’s health depends. 
  • Transpiration is the phenomenon by which water and other essential nutrients move through a plant from one cell to another. Through transpiration, plants are able to regulate their own temperature and absorb Carbon dioxide from air. Nutrient uptake from roots to the upper part of the plant is also done through transpiration. 
  • Temperature and Humidity play a vital role in yielding healthy, fresh and superior quality Cannabis. 
  • One thing should be kept in mind. VPD depends upon temperature and Humidity. Plant transpiration depends upon VPD. And the substantial growth of plant depends upon plant’s transpiration. 
  • Get your correct VPD with automated environmental controller to automate your grow room 
  • VPD is an important factor for the selection of facility systems especially when it comes to HVAC (Heating, Ventilation and Air Conditioning) Equipment. 
  • HVAC Equipment Design Temperature + Relative Humidity VPD Plant Growth 
  • Vapor-Pressure Deficit is pivotal for Greenhouse Regulation in case of Cannabis Cultivation. 
  • For plants to thrive in an indoor environment, VPD should be at a particular level. Value of VPD is different for every situation and every stage of growth in the table above shown correct VPD for flowering stage. 
  • As VPD depends upon temperature and humidity, there is a need to add or remove heat and moisture to or from the system, in order to keep the value of VPD maintained at a particular stage of growth. 
  • If value of VPD is very small, optimum rate of growth is not achieved. Different problems like mold and root rot arise because of it. 
  • If value of VPD is very large, the plant stomata will close in attempt to limit transpiration. This will result in occurrence of problems like tip burn and leaf curl. 

 

Bottom-line:
VPD is the deciding factor for healthy growth and cultivation of cannabis. So, if you want that your cannabis crop thrives and blossoms, you should control and set the appropriate value of VPD at every developmental stage, so that optimum growth can be achieved.