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Understanding VPD and its importance in cannabis cultivation

Cartier April 13, 2023

Vapor Pressure Deficit (VPD) is a critical factor to consider when cultivating cannabis plants. A deeper understanding of VPD and its importance in the growth process can significantly improve crop yield and overall plant health. This article will explore the concept of VPD, its role in cannabis cultivation, and how to optimize it for the best possible results.

What is Vapor Pressure Deficit (VPD)?

VPD measures the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at a specific temperature. In simpler terms, it is the difference between the actual and the saturation vapor pressures. VPD is usually expressed in pressure units, such as kilopascals (kPa).

The Role of VPD in Cannabis Cultivation

VPD plays a crucial role in cannabis plant growth and development, primarily by influencing the plant’s transpiration process. Transpiration is the evaporation of water from plant leaves through tiny pores called stomata. This process is essential for transporting nutrients, cooling the plant, and maintaining turgor pressure. An optimal VPD ensures efficient transpiration, which results in the following benefits:

  • Enhanced nutrient uptake: A proper VPD level promotes effective nutrient transport from the roots to the plant’s leaves and other parts, leading to better growth and development.
  • Optimal photosynthesis: Efficient transpiration helps maintain the right balance of carbon dioxide (CO2) and water vapor in the leaves, optimizing photosynthesis.
  • Improved pest and disease resistance: A well-regulated VPD reduces the likelihood of mold, mildew, and pests, as these thrive in high-humidity conditions.
  • Overall plant health and yield: Maintaining optimal VPD results in healthy cannabis plants and higher yields.

Determining the Ideal VPD for Cannabis

The optimal VPD for cannabis cultivation varies according to the plant’s growth stage. Here are some general guidelines:

  • Seedling/clone stage: 0.8-1.2 kPa
  • Vegetative stage: 0.8-1.2 kPa
  • Flowering stage: 1.0-1.5 kPa

These guidelines are not set in stone and may vary depending on factors such as strain and growing conditions. It is crucial to monitor and adjust the VPD throughout the plant’s life cycle to maximize growth potential.

How to Optimize VPD in Your Grow Space

To optimize VPD in your cannabis grow space, you need to manage both temperature and relative humidity (RH). Here are some tips to help you achieve the ideal VPD:

  • Monitor temperature and humidity: Use a digital hygrometer and thermometer to keep track of the temperature and RH in your grow space.
  • Adjust temperature: Use heaters, air conditioning, or ventilation systems to regulate the temperature in your grow area.
  • Control humidity: Employ dehumidifiers or humidifiers to maintain the desired RH levels.
  • Ensure proper air circulation: Use oscillating fans to promote even temperature and humidity distribution throughout the grow space.
  • Refer to VPD charts: VPD charts can help you determine the ideal VPD based on your grow room’s temperature and humidity levels.


To measure VPD, growers can use a combination of instruments and calculations or utilize specialized devices designed specifically for this purpose. Here are some options:

  1. Combination of Instruments and Calculations:
  • Digital hygrometer: This instrument measures relative humidity (RH) in your grow space. It provides you with the necessary data for calculating VPD.
  • Thermometer: A thermometer allows you to monitor the temperature in your grow space, which is another essential parameter for calculating VPD.

With temperature and RH values, you can either use a VPD chart or an online VPD calculator to determine the current VPD in your grow space.

  1. VPD Meters:

Some specialized devices on the market are designed explicitly for measuring VPD in your grow space. These VPD meters combine temperature, humidity, and VPD measurements in one device, simplifying the process and providing real-time VPD readings. Examples of such devices include the Pulse One Environmental Monitor, SensorPush Wireless Thermometer/Hygrometer, and other similar products.

  1. Integrated Environmental Controllers:

Advanced environmental controllers, such as the TrolMaster Hydro-X system, can monitor and control multiple environmental parameters, including VPD. These systems can measure temperature, humidity, CO2 levels, and VPD, and allow you to set custom parameters for your cannabis grow space. They can then automatically adjust the environment to maintain optimal conditions for plant growth.

Whichever method you choose, it’s essential to monitor VPD consistently and make necessary adjustments to your grow environment to maintain the ideal VPD throughout the various growth stages of your cannabis plants.

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