Vapor Pressure Deficit VPD( Best Cannabis VPD)
The global cannabis industry is rapidly expanding, with the report of Grand View Research estimating the legal cannabis market to be worth USD 16.7 billion in 2022. The industry is projected to grow at a compound annual growth rate of 25.4% from 2023 to 2030.
This industry is profitable, with multiple entry points to it, becoming a grower is an attractive option. However, to succeed as a cannabis grower, understanding the ideal growing conditions, including vapor pressure deficit (VPD), is critical.
Meanwhile, most indoor growers will encounter some tricky plant growth problems. Mold growth, slow and stunted growth, nutrient deficiencies, and overwatering are common problems for cannabis growers in the growing process.
These problems can occur when the vapor pressure deficit levels in the grow room are either too high or too low. A VPD that is too high can lead to transpiration stress and reduce the plant's ability to absorb essential nutrients. While a VPD that is too low can create humid conditions that are conducive to mold and mildew growth.
Maintaining the right cannabis VPD levels is essential for healthy growth and can help to prevent these problems. It is important to monitor VPD levels and adjust the environment.
But what exactly is VPD? Why is it so important? How can you use it? Read this article, and you'll know the answers.
VPD Meaning
What does VPD Stand For?
VPD meaning: "VPD is the abbreviation of Vapor Pressure Deficit. VPD is the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated. "
This is the definition of VPD provided by Wikipedia, and VPD has an important regulatory role in indoor cultivation applications such as greenhouses and grow rooms.
VPD Formula: VPD = SATURATION VAPOR PRESSURE (SVP) - ACTUAL VAPOR PRESSURE (AVP)
We will focus on more of VPD formulars and calculation here.
VPD kPa: one of the measurement units is kilopascals (kPa). It is a unit of pressure. Of course, it has other units of measurement, such as Paslas (Pa), hectopascal (hPa), millibars (mb), pounds per square inch (psi, lb/sqft), or kilograms per square meter (kg/sqm).
100 Pa = 1 hPa = 1 mb = 0.1 kPa
However, kPa is the most commonly used unit of measurement for VPD in the horticulture and agriculture industries because the numbers in VPD kPA are clean with whole numbers.
Influencing factors：The value of Vapor Pressure Deficit (VPD) is affected by several factors
① Temperature: As the temperature rises, the air's capacity to hold moisture also increases, leading to a decrease in VPD.
② Humidity: As the humidity increases, the air's moisture increases, which reduces the VPD.
③ Air pressure: Changes in air pressure can affect the VPD by changing the air's ability to hold moisture.
④ Plant type: Plants have different transpiration rates and water requirements, which affect the VPD .
⑤ Light intensity: Higher light intensity can lead to increased transpiration and evaporation, increasing the VPD.
⑥ Wind speed: Higher wind speeds can increase transpiration and evaporation, increasing the VPD.
⑦ Altitude: At higher altitudes, the air pressure is lower, which can affect the VPD.
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What is VPD in Plants
The optimal value of Vapor Pressure Deficit (VPD) depends on the type of plant and its growth stage.
For most plants, an ideal VPD range is between 0.4 kPa and 1.6 kPa. This range provides enough moisture for the plant to transpire and absorb nutrients while allowing for sufficient evaporation to cool the plant and prevent overheating.
However, for some plants, such as succulents and cacti, a higher VPD is acceptable, as they are adapted to arid conditions. On the other hand, for plants such as ferns and orchids, a lower VPD is preferred, as they are adapted to humid environments.
In general, monitoring VPD and adjusting the growing conditions as needed is recommended to maintain an optimal range for the specific plants being grown.
The benefits of maintaining the right temperature and humidity in your grow room:
Next, let's look at what range of VPD values are appropriate for cannabis.
Best VPD for Cannabis
In general, the VPD for cannabis is between 0.6 to 1.5.
But just like other plants, the ideal VPD range for cannabis plants can vary depending on the plant's growth stage. During different stages of growth, the plant's transpiration rate and water requirements will change, and so will the VPD range.
Ideal VPD for Seeding
Seedlings are delicate and sensitive to environmental changes, so maintaining appropriate VPD levels is crucial to ensure healthy growth and development.
For seedlings, a low VPD range is recommended, 0.6-1.0 kPa is a lower range compared to later stages of growth. A lower VPD range with higher humidity levels helps to reduce the risk of water stress on the seedlings while still providing adequate moisture for growth.
VPD for Veg
During the vegetative stage, cannabis plants require a higher VPD range compared to the seedling stage. The recommended VPD range for the vegetative stage is 0.8-1.2 kPa.
At this stage, plants are actively growing and require higher humidity levels to support transpiration and nutrient uptake.
Best VPD for Flowering
During the flowering stage of cannabis growth, plants are producing buds and flowers, and they require slightly lower humidity levels to prevent mold growth and maintain terpene production.
In this initial growth stages, your cannabis plants require low VPD as it keeps the stomata open. Allowing plants to increase thier absorption rates for better growth.
However, once your plants have reached the flowering stage, it is better to maintain a higher VPD level. This prevents the growth and development of mold and the spread of other pathogens to your established crop.
The ideal VPD range is considered to be between 1.0-1.5 kPa. Maintaining appropriate VPD levels is critical to ensure optimal plant growth and development, maximize yields, and potency.
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