Understanding Vapour Pressure Deficit (VPD) and Its Importance in Cannabis Cultivation

Understanding Vapour Pressure Deficit (VPD) and Its Importance in Cannabis Cultivation

Understanding Vapour Pressure Deficit (VPD) and Its Importance in Cannabis Cultivation

Vapour Pressure Deficit (VPD) is an essential concept in the world of cannabis cultivation. It plays a significant role in optimising plant growth, nutrient uptake, and overall yield. This article will provide an in-depth understanding of VPD and explain how it’s used in cannabis growing.

What is Vapour Pressure Deficit (VPD)?

VPD is the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at a given temperature. It is expressed in kilopascals (kPa) and indicates the air’s drying capacity. A higher VPD means the air can hold more water vapour, leading to increased evaporation and transpiration rates.

The Importance of VPD in Cannabis Cultivation

Cannabis plants rely on the process of transpiration to transport water and nutrients from the roots to the leaves. When the VPD is well-managed, it ensures proper transpiration, leading to:

Optimal nutrient uptake:

A balanced VPD helps maintain an efficient flow of nutrients throughout the plant, enabling healthy growth and development.

Improved photosynthesis:

With adequate transpiration, plants can maintain optimal leaf temperatures and gas exchange, promoting photosynthesis and energy production.

Enhanced pest and disease resistance:

Maintaining an ideal VPD reduces the risk of fungal infections and other diseases that thrive in high humidity environments.

Calculating and Managing VPD in Cannabis Growing

To calculate VPD, you will need to know the temperature and relative humidity (RH) of your growing environment. There are VPD charts and online calculators available to help you determine the optimal VPD for your cannabis plants.

The ideal VPD for cannabis varies throughout its life cycle:

Seedlings and clones: 0.4 to 0.8 kPa (70-75% RH at 22-25°C)

Vegetative stage: 0.8 to 1.2 kPa (60-70% RH at 22-28°C)

Flowering stage: 1.2 to 1.6 kPa (40-50% RH at 20-26°C)

To maintain the desired VPD in your grow room, consider the following steps:

Monitor temperature and humidity: Regularly measure the temperature and RH in your grow room with a digital hygrometer.

Adjust temperature: Use heating or cooling systems to regulate the temperature within the optimal range for your plants’ stage of growth.

Manage humidity: Use dehumidifiers or humidifiers to adjust the RH as needed. Additionally, proper air circulation and ventilation can help maintain humidity levels.

Keep plants well-watered: Ensure that your cannabis plants have access to sufficient water to support healthy transpiration.


Understanding and managing VPD is crucial for successful cannabis cultivation. By maintaining an optimal VPD throughout the plant’s life cycle, growers can optimise nutrient uptake, photosynthesis, and resistance to pests and diseases. Proper monitoring and adjusting of temperature and humidity levels will lead to healthier plants and improved yields.

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