Address: Foshan,China                Phone:         +86 13809220755             Email: [email protected]
 [email protected]

Unlock Optimal Growth: Using VPD Chart for Cannabis Cultivation

VPD charts are important in cannabis cultivation. They help growers regulate the temperature and humidity of the grow room for better cannabis growth.

What is a VPD chart? Next, let's take a closer look at VPD charts, learn about the types of VPD charts, and find out how to make the different VPD charts work for you during the growing process.

Table of Contents
show hide

What Is a VPD Chart

VPD charts, as the name implies, are charts that visually display VPD values.VPD charts visually represent data that can simplify the complex calculations that growers encounter in growing. Let's start with the components and types of VPD charts.

Components of a VPD chart

Proficiency with VPD charts begins with an understanding of their components.The components of a VPD chart typically include air temperature, relative humidity, and VPD values that play an important role in plant growth, as well as notes that supplement the VPD chart.

Air Temperature

Air temperature is usually the ambient temperature in the growing room, a basic element of the VPD chart. It affects the air's water vapor saturation, influencing the VPD value. Temperature fluctuations can stress cannabis, impacting its growth rate and health.

Relative Humidity

Relative humidity (RH) is the ratio of the moisture content of the air to the maximum water holding capacity at a given temperature. RH is important in VPD charts as it affects transpiration rate. High humidity can inhibit transpiration, while low humidity can cause excessive transpiration, harming the plant.

Vapor Pressure Deficit (VPD)

VPD is the difference between air moisture content and saturated moisture content. Proper VPD levels optimize transpiration, increase photosynthetic efficiency, and reduce pests and diseases, aiding healthy cannabis growth. The VPD chart helps growers find the optimal VPD range and adjust conditions for the best cannabis growth.

Annotations and Notes

The notes on a VPD chart explain the VPD value ranges represented by different colored areas, indicating the transpiration rate or appropriate planting stage. These notes vary depending on the type of VPD chart. To master VPD charts, it is important to pay attention to the annotations.

Types of Cannabis VPD charts

After clearly understanding the components of a VPD chart, let's take a look at what types of VPD charts are available. Different types of VPD charts serve different main purposes. There are three general types of VPD charts: VPD charts that simply show temperature and humidity, VPD charts that show different rates of transpiration, and VPD charts that show different stages of growth (mainly during the growing and flowering periods).

VPD charts for temperature and humidity: focus on showing VPD values at different temperatures and relative humidity conditions, with different colours to distinguish between VPD zones where cannabis grows optimally, VPD zones that are at a critical value, and VPD zones that are too high or too low and may be stressful for cannabis.

VPD charts representing different transpiration rates: focuses on showing the transpiration rate of cannabis at various VPD levels.

VPD charts representing different growth stages: Focuses on showing the optimal VPD range for different growth stages of cannabis.

The different types of VPD charts provide targeted perspectives that help us make adjustments to environmental parameters under specific conditions for better cannabis growth. With a basic understanding of the components and types of VPD charts, we will analyse the three main types of VPD charts in detail.

Temperature-Humidity VPD Chart

The Temperature Humidity VPD Chart demonstrates the optimal VPD range for cannabis growth, providing a visual guide to maintaining an optimal growing environment. The Temperature Humidity VPD Chart simplifies the complex interactions between the various environmental factors in the grow room, allowing growers to easily make precise adjustments to the growing environment based on the VPD Chart.

Understanding a Temperature-Humidity VPD Weed Chart

The temperature-humidity VPD chart is a two-dimensional chart with the vertical axis representing temperature and the horizontal axis representing relative or absolute humidity. Each grid on the chart corresponds to a specific VPD value.

The temperature-humidity VPD chart is a two-dimensional chart with the vertical axis representing temperature and the horizontal axis representing relative or absolute humidity. Each grid on the chart corresponds to a specific VPD value.

According to the annotated description on the chart we know that the different coloured areas in the VPD chart represent different ranges of VPD values. For example:

The green area represents optimal VPD, with VPD values usually ranging from 0.5 to 1.2. Being in this area indicates that the cannabis is thriving and there is no need to worry too much.

The yellow zone represents critical VPD, with VPD values usually between 0.4-0.5 or 1.2-1.4. Being in this range indicates that growers need to be aware and adjust VPD levels in a timely manner to prevent cannabis VPD from being too high or too low.

The red zone represents too high or too low VPD, with VPD values usually less than 0.4 or greater than 1.4. In this zone, cannabis is in a too-dry or too-wet condition and immediate action is needed.


(The referenced VPD chart is from PERFECT GROWER.)

Monitoring Real-Time Changes in Temperature and Humidity

Monitoring changes in temperature and humidity in real time is a prerequisite for using VPD charts. Paying close attention to changes in temperature and humidity and reacting and adjusting in a timely manner ensures that cannabis is always within the ideal VPD range.

Monitoring changes in temperature and humidity in real time is a prerequisite for using VPD charts. Paying close attention to changes in temperature and humidity and reacting and adjusting in a timely manner ensures that cannabis is always within the ideal VPD range.

Use of Thermometers for Accurate Temperature Measurement

Digital thermometers provide real-time temperature readings to help track temperature changes within the grow room. Growers can also place multiple thermometers in different locations within the grow room to get a complete picture of the temperature conditions within the room.

Monitoring Relative Humidity Using a Hygrometer

Just as important as temperature monitoring is humidity monitoring. Digital hygrometers provide accurate readings of humidity levels. Similarly, installing hygrometers in multiple locations in the grow room will help provide a complete picture of the humidity in the grow room so that adjustments can be made.

Adjusting Temperature and Humidity Levels in Conjunction with VPD Charts

Once accurate temperature and humidity data is obtained, adjustments are made to the growing conditions in the grow room based on the temperature and humidity VPD charts. Here are some strategies to help establish the optimal environment for cannabis cultivation:

Temperature Adjustment: this can be done using several types of thermostats. Common ones are air conditioners, heat pumps and heating tubes that transport heated or chilled water.

Humidity management: Relative humidity can be precisely regulated using dehumidifiers or humidifiers.

Optimising airflow: a range of fans, such as horizontal and vertical fans, can be used to disperse air to all parts of the grow room.

Enhance environmental isolation: Disturbances from the external climate can be minimised by appropriate insulation measures such as covering the walls, ceiling and floor of the grow room with foam boards, mineral wool, etc.

Through these strategies, the temperature and humidity of the grow room are monitored and adjusted to provide a stable and suitable growing environment for cannabis growth by proactively responding to changes in the environment.

Transpiration Rate - VPD Chart for Cannabis

Transpiration rate is the rate at which a plant releases water vapour into the atmosphere through its leaves and other parts. Not only does transpiration rate help plants absorb nutrients and cool down, it also maintains water balance. With the help of the transpiration rate VPD chart, growers can optimise the efficiency of water use in cannabis by monitoring and regulating the transpiration activity of cannabis to improve growth and yield.

How to Read the Transpiration Rate - VPD Chart

The basic components of the chart have been explained earlier and will not be repeated here. In order to read the VPD chart of transpiration rate, the most important thing is to read the annotation of the chart and the meaning of each colour block on the chart.

Transpiration rate VPD charts generally have four different coloured areas on the chart. These areas are usually labelled with the ideal VPD ranges for cannabis at different stages of growth (e.g. growing and flowering) and the optimal transpiration rate for the respective stage.


The blue zone indicates the optimal VPD range for cannabis in Propogation / Early Vegetative Growth, which is typically between 0.4 and 0.8. This area also indicates that cannabis in Propogation / Early Vegetative Growth is growing at a low transpiration rate.

The green area indicates the optimal VPD range for Late Veg / Early Flower cannabis, which generally ranges from 0.8-1.2. It also indicates that Late Veg / Early Flower cannabis is growing at a healthy transpiration rate.

The yellow zone indicates the optimal VPD range for Mid / Late Flower cannabis, which generally ranges from 1.2-1.6. It also indicates that Mid / Late Flower cannabis is growing at a high transpiration rate.

The red zone indicates that cannabis in Under / Over Transpiration is in the VPD range, which is generally between less than 0.4 or greater than 1.6. Also this area indicates that the cannabis is in the Under / Over Transpiration growth state. It needs to be adjusted immediately.


(The referenced VPD chart is from Growing Marijuana Forum.)

Recognizing Signs of Excessive or Insufficient Transpiration

Cannabis has different transpiration rate requirements at different stages of growth, which is well shown on the transpiration rate VPD chart. If a grower fails to meet the growth requirements of marijuana in a timely manner, it can lead to an abnormal transpiration rate, resulting in a host of problems for the plant.

Excessive transpiration can cause marijuana to lose too much water, which can lead to water stress and nutrient uptake problems. This is when marijuana may show symptoms of leaf curling, wilting, yellowing and burning.

Deficient transpiration can cause the plant to be unable to transport water and nutrients properly. Cannabis leaves in this state appear dark green or oily, while the leaves droop but do not wilt. Cannabis growth becomes slow or stagnant.

Monitoring and Using the VPD Weed Chart to Optimize Transpiration Rates

Wanting cannabis plants to grow at the proper rate requires regular testing and adjustments based on their growth stage and VPD charts. This includes regularly checking the VPD charts, measuring the temperature and humidity of the grow room and carefully observing the behaviour of the plants.

Managing Daily Watering Practices to Influence Transpiration

Daily watering directly affects the plant's water supply and root environment; adequate water allows the root system to consistently take up water and transport it through the plant's conduit system to the leaves, creating a transpiration stream. Under high VPD conditions, irrigation frequency can be increased or foliar sprays can be used to maintain an appropriate water status for the plant so that stomata remain open during the day to promote transpiration and photosynthesis. Under low VPD conditions, irrigation frequency or volume can be reduced to avoid waterlogging and root hypoxia. Root hypoxia can lead to reduced root uptake, affecting water transport and transpiration.

Observing Leaf Behavior as an Indicator of Transpiration

Leaf condition is a visual indicator of transpiration rate. Healthy leaves should be vigorous and slightly firm to the touch. Wilted, curled or discoloured leaves may indicate a transpiration problem. By observing these signs and referring to the VPD chart, the grow room environment can be adjusted in time to keep cannabis plants in optimal growing conditions.

Adjusting Fan Speeds to Regulate Transpiration

Wind speed directly affects the water vapour pressure on the surface of plant leaves and the microclimate around the stomata, so regulating fan speed can indirectly affect the rate of transpiration. Higher fan speeds increase air movement, which removes moisture from the leaf surface and reduces the temperature around the leaf. This increases the water vapour pressure difference between the inside and outside of the blade, which promotes transpiration. Proper placement and number of fans can help help keep cannabis plants at desired VPD levels by fine-tuning fan settings.

Proper use of a transpiration rate VPD chart can effectively manage cannabis transpiration rates to ensure healthy cannabis plants and increased yields.

Cannabis VPD Chart for Veg and Flowering Stages

There are two types of VPD charts we typically encounter when entering the different growth cycles of a cannabis plant: one type of VPD chart combines the optimal VPD values for the growing and flowering phases on a single chart, and the other type of VPD chart is a separate VPD chart that is customised specifically for each stage of production. Today, we will focus on the first type of VPD chart.

Clarify the Message of the VPD Chart

On this VPD chart that combines the optimal VPD values for the growing and flowering phases, combined with the annotated descriptions, it is known that the four different coloured zones correspond to different stages in the cannabis growth cycle:

The green area indicates the ideal VPD range for the reproductive/early growth phase, which is usually between 0.4 and 0.8, providing a mild environment for the initial growth of cannabis.

The blue zone indicates the ideal VPD range for the late growth/early flowering stage, usually between 0.8-1.2, providing support for cannabis as it transitions from nutrient growth to developing buds.

The purple area indicates the ideal VPD range for the mid/late flowering period, typically between 1.2-1.6, a range that helps optimise the bud maturation process.

The red area indicates an undesirable VPD range, with VPD values typically below 0.4 or above 1.6, indicating that cannabis may be under unfavourable environmental conditions for growth.


(The referenced VPD chart is from DIMLUX.)

Correlating Current Growth Stage with VPD Chart

Ensuring healthy cannabis growth requires growers to not only understand VPD charts, but also know how to adjust their environment to the specific needs of the plant.

For example, when cannabis enters the flowering phase, their needs for environmental conditions change in many ways compared to the growing phase. During the growing phase, cannabis grows rapidly and prefers high humidity and moderate temperatures, and needs to be kept at a low VPD. however, as it enters the flowering phase, cannabis needs lower humidity levels to prevent mould or other humidity-related problems from occurring.

This is where the grower needs to adjust the environmental settings to achieve a higher VPD value suitable for the flowering stage. However, it is important to note that growers should not be delusional and try to adjust lower VPD values to higher VPD values all at once. Drastic fluctuations can affect cannabis growth as well. Growers need to adjust the VPD values gradually to make a smooth transition to the optimal VPD range.

How to Measure the Data in the VPD Chart

VPD charts help to create the best growing environment for cannabis, and accurate data is the foundation for VPD charts to be effective. Data is generally measured in two ways, either manually by the grower or by relying on automated machines.

Manual Adjustment

Manual data measurement involves taking regular temperature and humidity readings, calculating VPD from the readings, and then manually adjusting environmental conditions to meet the needs of the plant.

Measuring Temperature

Growers can choose from a selection of accurate digital thermometers that can be placed at several key points in the grow room, especially in the plant canopy area. Regular monitoring of this data and timely adjustments to the heating or cooling system will ensure that temperatures are maintained at the optimum level for plant growth.

Measuring Humidity

Hygrometers are also dispersed throughout the grow room to obtain a full distribution of humidity. Fluctuations in humidity can be better understood through continuous monitoring. Adjust humidification or dehumidification measures as appropriate to maintain a stable and moderate environment conducive to healthy plant growth.

Calculating VPD Using Formula

In addition to the temperature and humidity specific data, the following formula is used to manually calculate VPD:

VPD = (1-100rh) x SVP

RH is the relative humidity and SVP is the saturated vapour pressure at a given temperature. The SVP value can be found in the reference table, or you can use an online calculator that simplifies the process. By entering temperature and humidity readings, VPD can be quickly determined and environmental conditions adjusted.

Automated Measurement Tool

Automated measurement tools offer a more convenient and accurate alternative to manual calculations. Tools for automated measurements provide continuous tracking and real-time feedback of temperature and humidity data, and even automatically adjust environmental conditions.

Pulse Grow is a leading brand of automated measuring tools, with equipment designed to accurately monitor the growing environment, providing growers with the data necessary to maintain optimum growing conditions for their plants.

The Pulse Grow device comes with several features that are extremely valuable to cannabis growers:

Pulse Grow Features

Real-time monitoring

Continuously tracks temperature, humidity and VPD to provide instant data

Data Logging

Records data over a period of time, historical data available

Alarm system

The system alerts when environmental conditions deviate from the preset range

User-friendly interface

Intuitive interface for easy setup and operation

How to Adjust VPD According to VPD Chart

VPD charts provide a framework for visualising optimal VPD. With these VPD charts, we are able to determine the specific needs of cannabis in terms of environmental conditions at different stages of growth and adjust our strategies accordingly.

Traditional Climate Control Solutions

Traditional climate control devices such as air conditioners and dehumidifiers are common tools used to manage the environment in grow rooms.

Using Air Conditioning to Control Temperature

Growers choose an air conditioning system that is appropriate for the size of the grow room and the heat load, and set the right temperature for the cannabis' stage of growth. Take care that the air conditioning vents are positioned to cover the entire grow area to avoid dead spots. Sometimes it may also be necessary to use a fan to help circulate the air and ensure that the temperature is evenly distributed throughout the grow room to avoid uneven heating and cooling.

Using Dehumidifiers to Control Humidity

The grower selects a dehumidifier that is appropriate for the size and humidity load of the grow room and sets the appropriate humidity level for the stage of growth of the plants. The dehumidifier can be placed in the area of the grow room with the highest humidity, usually in a densely planted area or near a water source. Growers should periodically adjust the dehumidifier's settings and operating strategy to ensure that the humidity conditions at each stage meet the plants' needs.

Drawbacks of Traditional Solutions

Despite the advantages of traditional climate control methods, there are some shortcomings

High Energy Consumption and Costs

As energy-intensive equipment, the cost of running air conditioners and dehumidifiers undoubtedly poses a challenge for growers seeking economies of scale. Air conditioners and dehumidifiers are controlled by two separate systems, and when the two separate systems are in operation, they may interfere with each other, affecting the efficiency of each.

For example, dehumidifiers release a certain amount of heat during operation, and air conditioners, in addition to their own energy requirements, need to use additional energy to offset the heat released by dehumidifiers when they reach the temperature target set by the grower. In addition, the air conditioner performs a certain degree of dehumidification along with cooling, which may lead to excessive dehumidification in the process, causing the humidity level in the grow room to fall below the set value. This situation requires the humidifier to operate in order to maintain a suitable humidity environment.

This conflict affects cooling and dehumidification efficiency and increases energy consumption.

Inconsistent Temperature and Humidity Control

Air conditioners and dehumidifiers play an important role in regulating temperature and humidity, but they can lead to unstable temperatures and humidity in certain areas, which in turn can affect the growth of cannabis plants.

If the equipment is concentrated at one end or in one corner of the grow room, it may or may not result in the neighbourhood being too cold or too dry, while areas away from the equipment may have higher temperatures and humidity. In addition to this, the cool or dry air produced by air conditioners and dehumidifiers needs to be evenly distributed throughout the grow room. Inadequate air circulation can result in insignificant changes in temperature and humidity in some areas, while other areas may vary too much. Plants in different areas are subject to different environmental conditions, which may result in uneven growth and affect overall yield and quality.

High Labour Costs

The use of air conditioners and dehumidifiers for temperature and humidity control in grow rooms, while providing precise environmental control, also entails high labour costs. A significant investment of time, manpower and expertise is required to ensure efficient operation of the equipment and stable environmental conditions. For example, to ensure that the temperature and humidity in the growing room is always in the optimal range, environmental parameters need to be monitored and fine-tuned manually in real time. In addition, air conditioners and dehumidifiers require regular cleaning of filters, replacement of parts, etc., which usually requires hiring specialised technicians or outsourcing to specialist companies.

To overcome these drawbacks, many growers have begun using automated climate control systems. These systems provide more precise control, lower energy consumption and less human intervention.

Efficiently Manage Grow Room Environment with Altaqua HVAC System

With the Altaqua Grow Room HVAC System, you can be more efficient in managing your grow room environment.


Combine Reheat Coil and Outdoor Condenser Unit

Unlike conventional dehumidifiers that release heat while dehumidifying, the Altaqua Grow Room HVAC System's Outdoor Condenser Unit condenses refrigerant vapour into a liquid by releasing heat into the outdoor environment, which in turn performs the cooling cycle and humidity regulation. The indoor reheat coil will recover heat from the refrigerant condensation in order to reheat the dehumidifier air back into the grow room, which ensures that the grow room does not become too cold after the dehumidification phase, ensuring the ideal grow room temperature. Combining the indoor reheat coil with the outdoor condenser provides unparalleled adaptability and maintains environmental consistency, maximising plant growth potential.

Precise Temperature and Humidity Control

The Altaqua Grow Room HVAC System uses dew point control instead of relative humidity. Traditional dehumidification systems measure RH, which is sometimes misleading due to its temperature dependency. Grow room temperatures change frequently due to equipment such as grow lights, which can also change RH levels frequently. Dew point is temperature independent and remains stable to provide a more accurate representation of actual humidity conditions.Altaqua grow room hvac systems provide both temperature and humidity settings, resulting in more reliable and efficient dew point control for consistent yield quality and quantity.

Intelligent Automation

Another highlight of the Altaqua Grow Room HVAC System is intelligent automation. The grower can program the conditions of the growing environment according to growth stage, day/night cycle, etc. to optimise each stage of plant development. This automation reduces manual intervention and allows the grower to focus on other key aspects of the growing process.

Precision Supply Air flange offers Customizable Airflow

Additionally, the Altaqua Grow Room HVAC System is equipped with precision supply air flanges that provide growers with adjustable airflow direction to meet the nuances of each grow room as closely as possible. This feature facilitates an even distribution of airflow within the grow room. Uniform airflow helps to reduce the occurrence of microclimates and promotes temperature and humidity balance in the grow room, providing consistent growing conditions for all plants.

The Altaqua Grow Room HVAC System is an all-in-one system that provides precise temperature and humidity control for commercial growers, and is the ultimate solution for a wide range of controlled agricultural environments, providing the most energy-efficient and cost-effective solution.


In cannabis cultivation, VPD charts are an important tool for optimising growing conditions. By understanding the components and types of VPD charts, growers can simplify complex calculations and create optimal growing conditions based on VPD charts. Temperature, relative humidity and vapour pressure difference (VPD) are the key elements of these charts. Used correctly, VPD charts allow for precise temperature and humidity control, ensuring consistent quality and yield.

In addition, tools such as the Altaqua grow room HVAC system provide efficient and precise climate control. By combining reheat coils, outdoor condenser units and intelligent automation, the system optimises temperature and humidity levels. Precision air supply flanges further customise airflow to create a consistent environment for all plants.

Understanding the VPD charts and adopting these advanced systems can significantly improve the efficiency and productivity of cannabis cultivation, ultimately resulting in better growth and higher yields.


1.What is a VPD chart, and why is it critical for cannabis cultivation?

VPD (Vapor Pressure Deficit) charts are a tool for helping cannabis growers fine-tune the temperature and humidity in the growing environment to optimize plant transpiration. Transpiration is critical for plant nutrient uptake and water regulation, and using VPD charts can help growers prevent mold growth, nutrient deficiencies, and water stress, promoting plant health and increased yields.

2.How do you interpret VPD charts for cannabis?

VPD charts present data on axes: temperature is labeled on the vertical axis, and relative humidity is labeled on the horizontal axis. The points on the chart correspond to specific VPD values, guiding the grower through the plant's transpiration status. Color coding often indicates the ideal VPD range for different growth stages, allowing growers to identify and adjust to the right conditions visually.

3.What should be the ideal VPD range for cannabis seedlings?

The ideal VPD range for cannabis seedlings is recommended to be between 0.4 and 0.8 kPa. This lower VPD range supports higher humidity, which is critical for the early stages of seedling growth and helps to prevent drying out of leaves and roots to ensure healthy growth.

4.How can I use the VPD chart to adjust my growing environment?

Based on the VPD chart, growers can use air conditioners to regulate temperatures and dehumidifiers or humidifiers to control humidity to match the recommended zones on the chart. Real-time monitoring tools such as thermometers and hygrometers provide data to support precise adjustments. Automated systems, such as Pulse Grow or Altaqua, can further enhance the accuracy and stability of environmental controls.

5.How can VPD charts help boost cannabis production and health?

VPD charts support optimal transpiration rates for plants by maintaining the right temperature and humidity balance. This balance is critical for efficient nutrient uptake and preventing diseases such as mildew and nutrient deficiencies. Plants thrive under proper VPD conditions, leading to higher yields and better health.

6.Can VPD charts prevent common problems in cannabis cultivation?

Indeed, VPD charts help prevent common growing problems, including mold, nutrient deficiencies, and water stress, by optimizing environmental conditions. Good VPD management ensures that plants maintain a balance of water and transpiration, which promotes healthier growth and higher yields.

Share with your friends:

Popular Blogs on Altaqua:

Get HVAC Brochure?

Get HVAC Brochure

Get HVAC Brochure?

Altaqua Form 1