What is VPD or Vapor Pressure Deficit?
Denis Manzetti
Summary:
I. The Fundamental Concept of Vapor Pressure Deficit (VPD) and its Significance.
II. Exploring Leaf Vapor Pressure Deficit (LVPD).
III. Accurate Methods for Calculating VPD and LVPD in the Indoor Growing Environment.
IV. Relevance of LVPD in Different Phases of Plant Development.
V. Efficient Strategies for Correcting Discrepancies in the VPD.
Precision indoor cultivation demands meticulous control of environmental conditions, with Vapor Pressure Deficit (VPD) being a crucial factor in this process. This article aims to provide an in-depth analysis on the subject, elucidating the essential elements to optimize healthy plant growth and development.
Understanding Vapor Pressure Deficit (VPD) in Cannabis Cultivation
I. The Fundamental Concept of Vapor Pressure Deficit (VPD) and its Significance:
VPD, known as Vapor Pressure Deficit, is an agricultural measurement that evaluates the difference in pressure between moisture inside and outside plant leaves. This metric plays a vital role in cannabis cultivation, directly influencing the health and resilience of plants in the face of adverse biotic and abiotic conditions.
Cannabis breathes through mouth-like openings on the underside of its leaves called stomata. 
These stomata inhale carbon dioxide (C02) and exhale oxygen and moisture .
With an ideal VPD, your plants will open their stomata and transpire more quickly, fueling photosynthesis for vigorous growth. By transpiring at the ideal rate, your plants will also be able to increase nutrient absorption. And, of course, open stomata mean a greater amount of CO2 can be absorbed, leading to better overall development.
As you can see, achieving the correct VPD is critical to maximizing plant performance.
II. Exploring Leaf Vapor Pressure Deficit (LVPD):
LVPD represents the disparity between Saturated Vapor Pressure (SVP) and Relative Humidity in the growing environment. It is essential to understand that, due to transpiration, leaves tend to be slightly cooler than the surrounding environment. This distinction is fundamental for an accurate assessment of the plant's internal environment.
III.Accurate Methods for Calculating VPD and LVPD in Indoor Growing Environment:
To calculate VPD, you need to know the temperature and relative humidity of the grow space, along with the saturation vapor pressure (SVP), which varies depending on temperature. This data is used in a specific formula to determine VPD, allowing for precise adjustments to environmental conditions.
To calculate the Vapor Pressure Deficit (VPD) manually, it is first necessary to determine the Saturation Vapor Pressure (SVP) corresponding to the ambient temperature. This can be done using the equation:
S V P = 610 , 78 × and (T ÷ T + 238 , 3 ) × 17 , 2694
After obtaining the SVP value for the specific temperature, the following formula is applied to calculate the VPD:
V P D = ( 100 − RH ÷ 100 ) × S V P
RH = Relative Humidity
To illustrate, let's consider a cultivation area with a temperature of 23°C and relative humidity of 58%. Consulting the SVP table, the corresponding value of 23ºC is 2809 . Applying the VPD formula, we have:
V P D = ( 100 − 58 ÷ 100) ×2809
Like this,
V P D = 0.42 × 2809 = 1179.78 Pascals
Subsequently, the value in Pascals must be converted to kiloPascals (kPa), dividing it by 1000:
In this way, we complete the VPD calculation, providing a precise measurement to adjust environmental conditions for optimal plant cultivation.
DeepGarden's Growbot line for precision cultivation has sophisticated sensors and state-of-the-art software that ensure you always have the VPD, as well as other important variables of your environment at hand to take the necessary measures so that the conditions are always ideal for each stage of the plant's life.
IV. Relevance of LVPD in Different Phases of Plant Development:
Each stage of the cannabis life cycle demands an ideal LVPD range. From the early seedling stage through the flowering phase, it is crucial to maintain an adequate moisture balance to promote vigorous growth and minimize the risk of pathogens and disease.
Check below some data provided by Pulsegrow with the LVPD parameters for plants in their different stages, with the strongest green being the ideal range:
For early stages of development, such as seedlings and clones , it is essential to create an environment with higher humidity levels to promote vigorous growth and effective rooting.
Chart for clones & seedlings
In this context, the ideal Leaf Vapor Pressure Deficit (LVPD) is between 0.8 kPa and 1.0 kPa, providing optimal conditions for the initial development of plants.
During the vegetative stage, known as vega, plants' demands for moisture gradually decrease as they establish a robust leaf structure and expand their roots.
Vegetation chart (vega)
At this stage, it is recommended to maintain the LVPD within the range of 1.0 kPa to 1.2 kPa, ensuring an adequate balance between transpiration and nutrient absorption.
Example: If your vegetation environment has a temperature of 28ºC and relative humidity of 50%, the VPD of your environment is 1.6kPa, which is too high and will harm the development of your plant, consequently the quality and final yield.
When entering the flowering phase, where priority falls on flower and fruit production, it is crucial to further reduce humidity levels to mitigate the risks of pathogen infestation and mold development.
Flowering chart
Graphics: Pulse Grow
Therefore, it is recommended to maintain the LVPD between 1.2 kPa and 1.6 kPa during the flowering stage, aiming to preserve plant health and optimize harvest quality.
V. Efficient Strategies for Correcting Discrepancies in the VPD:
VPD control can be achieved through devices such as humidifiers, dehumidifiers, air conditioners, and heaters. By maintaining temperatures and relative humidity within ideal parameters, it is possible to guarantee an environment conducive to the healthy development of plants. And to control this equipment efficiently, remember that with Growbot all this control is automatic, in addition to being able to monitor and intervene through our app from anywhere in the world.
Conclusion:
Understanding and managing Vapor Pressure Deficit (VPD) is essential to maximizing the growth and health potential of cannabis plants. Precision in controlling environmental conditions, including temperature and humidity, plays a key role in successful cultivation. In this context, DeepGarden emerges as an indispensable ally for growers, offering precision cultivation solutions that automate and optimize control of the cultivation environment. With its ability to constantly monitor and adjust environmental parameters to ensure an ideal VPD at all stages of the plants' life cycle, the Growbot line for precision cultivation provides consistent, high-quality results, thus exploiting 100% of the genetic potential of your plants. plants and making future generations come with even stronger and more vigorous cultivars.
We hope this analysis provides a deeper understanding of the crucial role of VPD in indoor cannabis cultivation. For additional consultations or personalized guidance, do not hesitate to request consultancy or assistance to implement your project and be sure to follow our social media for regular updates on effective cultivation practices.
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