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Lesson 1, Topic 1
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Optimal VPD ranges for cannabis growth stages

Cartier April 13, 2023

Cannabis cultivation is an intricate process that requires a delicate balance of environmental factors to ensure optimal growth and yield. One of the key factors influencing plant growth is the vapor pressure deficit (VPD), which is the difference between the amount of moisture in the air and the amount the air can hold when saturated. Maintaining the appropriate VPD range for each growth stage is essential to support plant health and enhance overall productivity. This article will provide a comprehensive overview of optimal VPD ranges for each cannabis growth stage, from seedlings to flowering.

Understanding Vapor Pressure Deficit (VPD)

VPD is a measure of the difference between the actual vapor pressure and the saturation vapor pressure at a given temperature. It is expressed in kilopascals (kPa) and provides valuable insights into the plants’ ability to transpire and absorb nutrients effectively. Higher VPD values indicate drier conditions, whereas lower VPD values suggest more humid environments. Proper VPD management is crucial for cannabis plants, affecting essential processes such as photosynthesis, transpiration, and nutrient uptake.

Optimal VPD Ranges for Cannabis Growth Stages

a) Seedlings and Clones

During this delicate stage, cannabis plants require a higher humidity level to promote root development and prevent dehydration. It is crucial to maintain a VPD range of 0.4 to 0.8 kPa. High humidity levels of around 70% to 80% and temperatures between 20°C and 25°C (68°F and 77°F) are ideal for supporting the development of young cannabis plants.

b) Vegetative Stage

As the cannabis plant transitions to vegetative, it requires slightly drier conditions to encourage leaf growth and prevent mold and mildew. The optimal VPD range for this stage is between 0.8 and 1.2 kPa. Maintain a relative humidity of 40% to 70% and temperatures between 22°C and 28°C (72°F and 82°F) to promote robust vegetative growth.

c) Flowering Stage

The flowering stage is the most critical phase for cannabis plants, as this is when the buds develop. The ideal VPD range for this stage is between 1.0 and 1.5 kPa. A lower humidity level of 40% to 50% and temperatures between 20°C and 26°C (68°F and 79°F) are crucial to minimizing the risk of bud rot and other diseases. During the last two weeks of flowering, you can further reduce the humidity to 30% to 40% to encourage trichome production and enhance resin development.

Monitoring and Adjusting VPD

It is essential to monitor the temperature and humidity levels in your grow room to maintain the optimal VPD range for each growth stage. Using a digital hygrometer and thermometer can help you track these values accurately. To adjust the VPD, you can use humidifiers, dehumidifiers, air conditioners, or heaters, depending on the specific needs of your cannabis plants.

Conclusion

Maintaining optimal VPD ranges during each cannabis growth stage is essential for promoting healthy plant development, maximizing yield, and preventing disease. By understanding and managing VPD levels, growers can optimize their cultivation practices and ensure a successful harvest. Remember to monitor temperature and humidity levels regularly, and make adjustments as needed to maintain the ideal VPD range for your cannabis plants.

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