Vapor Pressure Deficit VPD (Best Cannabis VPD)

Upgated: Oct. 30 ,2025 · 20 min read

By 2023, the global cannabis industry has reached unprecedented heights, with Grand View Research projecting the legal cannabis market to reach a staggering $57.18 billion. Currently, this dynamic market not only continues to grow but is poised for explosive expansion.

However, while indoor cannabis cultivation offers substantial profits, it also presents significant challenges. Growers frequently encounter issues such as mold proliferation, stunted plant growth, nutrient imbalances, and persistent overwatering.

These problems are often closely linked to improper management of vapor pressure deficit (VPD) within indoor cannabis growing environments.

Therefore, the ability to precisely control temperature and humidity to achieve the ideal VPD range is crucial for cannabis to grow healthily and maximize yield.

But what exactly is VPD, why is it important in cannabis cultivation, and how can we effectively utilize VPD to achieve the desired results? We will now discuss these questions together, revealing the role of VPD in cannabis.

Interpretation of Vapor Pressure Difference (VPD)

In order to appreciate VPD, it is important to understand that VPD is more than just a scientific term or technical calculation; rather it has implications throughout all facets of controlled environments.

VPD is not just a technical term; it's a critical factor that influences every aspect of plant growth in controlled environments.

What does VPD stand for?

VPD is the abbreviation for Vapor Pressure Deficit. It measures not the actual moisture content present in the air, but the air's potential moisture capacity. It can be understood as a gap—the difference between the actual moisture content in the air and the maximum amount of moisture the air could hold if it were completely saturated.

VPD Meaning

Vapor Pressure Deficit (VPD), represents the difference between the moisture present in the air and the maximum moisture the air can hold when fully saturated.

Vapor Pressure Difference Formula

The formula for calculating vapor pressure difference is straightforward:

Vapor Pressure Difference = Saturated Vapor Pressure (SVP) − Actual Vapor Pressure (AVP)

But if you are treating this computation as just that, a number, then you’re getting it wrong. This is just a rule of thumb indication on what happens between air humidity and plant well-being.

Unit of Measurement

When measuring VPD, multiple units are involved:

• Kilopascals (kPa) — a common pressure unit.
• Pascals (Pa) and hectopascals (hPa).
• Millibars (mb).
• Pounds per square inch (psi, lb/sq in).
• Kilograms per square meter (kg/m²).

Of these, kPa is most commonly used in horticulture and agriculture because of the perceptual representation of VPD values. Its simplicity makes kPa the recommended unit for accurate VPD measurement in various cultivations:

100 Pa = 1 hPa = 1 mb = 0.1 kPa

All these factors influence VPD, thereby affecting the overall growing environment and health status of cannabis plants.

The ideal plants need VPD in the range of species and stages.

Most plants are happy at a VPD of 0.4-1.6 this is when you get the best bang for your buck from liquid nutrient uptake and keep it cool without full runaway evaporation happening.

Optimum range is individual to specific plants though: (desert) succulents love high VPD, ferns prefer low VPD.

There are many benefits to optimizing VPD for your grow operation:

• Promotes optimal plant growth
• Controls pests and diseases
• Saves energy
• Enhances quality
• Increases yield

This is especially relevant for cannabis, because as we’ll learn next it is important to know what the optimal VPD range should be.

What's up with Vapor Pressure Deficit (VPD)?

To appreciate why VPD is important for growing cannabis, you need to understand that it controls how well water and nutrients are taken up by plants as they grow. Even more, it directly affects the plant’s growth, yield and quality.

Importance of VPD for Plants

Fundamentally, VPD’s primary role in cannabis growth has to do with how water evaporates from the plants. To gain a better understanding on the relevance of VPD for cannabis water transpiration, let’s delve into what plant transpiration is all about.

Transpiration of Plants

As a basic rule of thumb, think of transpiration as the same process you use when breathing. It’s simply when water is lost from leaves. This flux begins back in the roots, which take up water and send it to leaves via xylem vessels.

As it kicks out through its foliage, water vapor cools a plant and unlocks passage for nutrients.

It’s also a way for plants to discharge an excessive amount of water, reducing the likelihood of damage to their foliage. And so it is not just a process. for plants, transpiration is the life line.

Stomata Opening

Stomata are the small openings' at a leaf blade where gas exchange has taken place. They modulate the availability of CO2 for photosynthesis and loss of CO2, water vapor. Here’s how the stomata work: they open and close under different conditions, including in response to light, humidity and the needs of the plant’s insides for water.

Under optimal photosynthetic conditions, stomata are wide open while in high humidity or low light, they close to save water and energy.

Carbon Dioxide Uptake

Carbon dioxide is used in photosynthesis. Plants take up carbon dioxide from the air through stomata, and that is combined with light energy in chloroplasts to produce sugars and starches. This is the fundamental process for growth and energy generation in plant.

Nutrient Uptake by Roots

Roots are not just anchors, they are actively involved in taking up water and nutrients from the soil. They receive important nutrients from the soil that flow through the plant.

This nutrient uptake process is directly linked to the plant's transpiration and the VPD has an effect on this efficiency.

Plant Stress

When VPD levels are not in balance, plants become stressed and this affects their general health and growth. High VPD can result in dehydrative stress, wilting, nutrient imbalance and reductions in growth.

On the other hand, low VPD can cause over-wet conditions that favour fungal diseases and discourages vital gas exchange. Therefore, to keep the VPD in an appropriate range is key for low stress and healthy grow.

VPD and Indoor Cultivation

The importance for controlling VPD is even greater in greenhouse production given the controlled environment. This is where VPD becomes crucial for growers as they try and dial in their optimal conditions for growing cannabis.

VPD Requirements for Cannabis

There is no one-size-fits-all ideal VPD when it comes to cannabis plants — the ideal VPD depends on their stage in growth. That said, these are "guidelines", as actual parameters will vary based on strain, and environmental issues etc. VPD should be actively monitored and adjusted to keep an optimal growing condition.

An excessive VPD too high can cause overt transpiration stress that adversely affects plant growth and yield. Conversely if VPD is too low then mold and powdery mildew can grow on leaves – this is not good for plants.

The Importance of VPD is very important for health cannabis plants because they grow under conditions that must meet their needs.

In Summary Vapor Pressure Deficit (VPD) is a cornerstone concept for both cannabis growth and plant growth in general. A complex system for the control of important activities such as transpiration, stomata behavior and CO 2 uptake, nutrient intra transportation and stress response.

This is especially true for indoor growing conditions where the environment is closely managed. VS By helping keep an ideal VPD, growers can improve plant health, yield production and stop common growing problems.

Having a clear understanding of what VPD to maintain at the different stages of growth for your cannabis plants, in addition to how to adjust it based on their needs will help make you successful with realizing successful and sustainable plant growth.

VPD and Indoor Climate

Within the intensive life of an indoor cannabis garden, Vapor Pressure Deficit (VPD) has become a key sign that is strongly related to two of our most important indoor climate components: temperature and relative humidity. Therefore, it is critical to carefully watersource these variables to allow your marijuana plants to flourish.

Temperature

Temperature largely influences the optimal VPD levels for cannabiculture. The ideal temperature for indoor growth typically ranges between 65°F and 80°F If temperatures drop to less than 65 degrees, plant growth slows down because rates of photosynthesis slow.It makes the plants more susceptible to root-targeting anaerobic pathogens, which can cause mold and disease.

On the contrary, over 80° will cause stress on your plants, wasting energy that could be focused on growth and development to keeping cool. So maintaining an optimum temperature is critical for comfortable ambient and to create the perfect environment which assists in generating optimal VPD, and well-being of your plants.

Relative Humidity

Also included in the VPD function is the relative humidity (RH). The exact perfect RH values for growing marijuana are not well defined, these vary depending on each growth phase and strain, however very low or high levels can impact negatively your plants. At 100% RH, the air has actually reached its capacity and can no longer absorb water from a plant's leaves (from evaporation); this is one 'definition' of not partial pressure, but full pressure by way of reaching vapor saturation pressure.

Conversely, when RH is too low, the plant's stomatal closes to conserve water and transpiration may be inhibited. This fine-tuned RH balance is key to maintaining a VPD that encourages successful transpiration, nutrient uptake and cannabis plant (as a collective) growth.

Light Intensity

Light intensity significantly impacts VPD in the indoor growing environment. Plants utilize light for photosynthesis, and the rate of photosynthesis influences transpiration. Higher light intensity can increase transpiration rates, thereby affecting VPD.

For those growing indoors it is not simply a matter of providing enough … but also understanding its impact on VPD and therefore plant health. Well balanced light intensity will help plants to photosynthesis efficiently and at the same time no excessive transpiration, corresponding to the best VPD for perfect growth.

Altogether, the combination of temperature and relative humidity in the indoor environment is important when it comes to VPD. The correct regulation of these elements provides an optimal environment for marijuana promoting strong development and results. As a grower, your ability to tweak these environmental factors will greatly affect how well or even what you are able to grow.

Best VPD for Cannabis / Ideal VPD for Different Stages of Growth

In general, the VPD for cannabis is between 0.6 to 1.5.

However, similar to other vegetation, the optimal VPD for cannabis plants shifts with their growth stages. As these plants progress through various stages, their transpiration rates and water needs alter, affecting the suitable VPD range.

Optimal VPD for Seedlings and Clones

The young plants are fragile and highly susceptible to stress so it is important that the VPD remains in suitable ranges enabling optimal plant growth.

The lower range (0.6–1.0 kPa) is suggested for seedlings, being a narrower range value than during later stages of growth. Keeping VPD as low as possible with high humidity, allows to reduce the water stress risk in seedling and providing enough water for growth.

Ideal VPD for Vegetative Stage (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 / Ideal VPD for Flower Stage

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.

Here is a list of recommended VPD ranges for each growth stage of cannabis, it will be clearer.

It is important to note that the ideal VPD range will vary depending on various factors such as temperature, humidity and air movement. Therefore, it is critical to monitor and adjust VPD as needed.

VPD at Night: A Critical Aspect for Cannabis Cultivation

Management of VPD at night It is easy to manage VPD in day-time, and during the nights different set of challenges and opportunities for controlling VPD exists.

Understanding VPD's Night Role

In the night, when no photosynthesis takes place and transpiration is greatly reduced, VPD exerts an entirely different effect on plant physiology. Growers must change with these trends in order to maintain an optimal growing environment for their marijuana plants.

Plant Night Activities and VPD

When the sun sets, cannabis plants change their ways. Stomatal closure decreases transpiration, but respiration of the plants continues to generate CO2. This shift in plant behavior influences VPD and needs to be closely tracked and corrected by growers.

Also, moisture is not released into the atmosphere as much due to the lower transpiration rates during nocturnal period and hence, VPD values are affected. Growers need to know about this dynamic so that they do not create conditions that can threaten the health of the plant or promote disease.

VPD Effects on Stomatal Behavior and Transpiration

Controlling VPD during the night is important to help maintain a proper moisture-temperature balance. At the same time, when VPD is too low it results in high humidity and a potential environment for mold and mildew. Conversely, when the VPD is too high it becomes stressful to the plant and can compromise nutrient and water uptake.

Controlling the VPD in night for Healthy Cannabis

Good night VPD handling is based on few key rules keeping the plants healthy and system running optimal.

Disease Prevention and VPD Stability

Disease prevention is served by keeping the VPD stable at night. Night time RH can be lower which may limit some molds and mildews (bud rot, powdery mildew). This preventative method is important for maintaining healthly canna crops.

Aligning Night and Day VPD

Scaling VPD for day and night is an important requirement to achieve homogeneous growth. Plants might transpire less at night than during the day, but they do still respire CO2 and you also need your VPD to be quite close to what it is during the day. The key to your plants health is going to be avoiding the large VPD swings.

Adjustment of Night VPD Based on Stages of Growth

There are varying VPD requirements for different growth stages of cannabis during the dark period, to reach maximum development.

VPD for Seedlings and Clones

Higher humidity and lower VPD are better for seedling/cloning stage. When the plants are this young, a target VPD range of 0.6 to 1.0 kPa, or towards the lower end especially, supports tender growth.

Vegetative and Flowering Stages VPD

Plants are stronger during the vegetative period and therefore, we may now decrease our humidity levels and increase the VPD a little. When in flower you’ll want to be at the top end of this range, say between 1.0 -1.5 kPa to avoid humidity problems around those delicate buds.

Observation and tuning are crucial in all these stages. By controlling and adjusting the VPD according to the needs of plants in different growth periods, growers can have healthier plants and achieve higher yields.

To recap: Nighttime VPD is a complex aspect of growing cannabis, but it’s crucial. Growers that track and adjust VPD levels based on time of day, as well as life cycle phase, will be able to optimize the environment for the best possible flowering performance given these tenets.

Cannabis VPD Chart

VPD charts are pictorial diagrams, which express the interrelationship of temperature, relative humidity and VPD.

VPD graphs can also assist growers in making decisions on watering, ventilation and other grow conditions to ensure plants are kept at an ideal VPD.

How To Read VPD Chart

To interpret a VPD chart, you have to know the following:

X-axis: The x-axis is the temperature, expressed typically in Celsius or Fahrenheit.

Y-axis: The Y-axis stands for relative humidity in percentage.

Zones: The graph is divided into multiple zones (coloured or shaded areas representing different ranges for VPD). For instance, green could show an acceptable VPD range for the majority of plants, and red could indicate a VPD that was too high and might lead to stress.

This is the VPD chart for Cannabis.

The VPD chart for marijuana growers is the same as a regular vpd chart however with vpd levels that are ideal for cannabis.

• Vegetative growth: 0.8~1.2 kPa
• Flowering: 1.0~1.5 kPa

The graph would then be split into zones of various colors or shading, each signifying a set range of VPD for cannabis. For instance a green VPD zone may indicate the perfect optimum range for veg, and a yellow may represent one that is nearing the upper threshold when you flip to flower.

How to Use VPD Charts

Follow these steps to use the VPD chart:

VPD Chart for Flower of Cannabis

VPD charts help cannabis growers optimize growing conditions for their plants by showing the ideal Vapor Pressure Deficit range for each plant species.

By regularly measuring temperature and relative humidity, plotting the current VPD range on the chart, and adjusting growing conditions as needed, growers can maintain an optimal VPD for healthier, more vigorous plant growth and better yields. Especially at this stage of flowering, the vpd chart is very important.

How to Calculate Vapor Pressure Deficit

To better understand how Vapor Pressure Deficit affects your plants, it is important to study it in depth. There are two terms that directly control the VPD of your grow room.

Saturation Vapor Pressure (SVP): The maximum water vapor content that air is capable of holding at a particular temperature. The warmer the temperature, the higher the air's capacity to hold water vapor and thus the greater a SVP. SVP is temperature dependent, and it is one of the parameters used in calculating VPD.

Actual Vapor Pressure (AVP): The quantity of water vapor existing in the atmosphere at a temperature. AVP is sensitive to the temperature and relative humidity of air. AVP values increase with higher temperature and relative humidity.

AVP and SVP are related in that the most AVP your grow room can contain is its SVP. It’s important to fully grasp these terms because knowing them will allow you to calculate your grow room’s VPD in the next part below.

Two Methods of Calculating VPD

Vapor Pressure Deficit (VPD) can be calculated using two methods:

Air VPD Calculation

There are two essential elements we need to know in order to calculate the VPD of the air: The air temperature (either in °C or °F) Relative humidity, expressed in percentage. Then you can choose to use dew point or wet bulb temperature to get the precise measurement from there.

For the dew point determination process:

1. Compute the dew point temperature (°C or °F) using a dew point calculator/temperature formula.

2. To find the VPD, subtract the dew point temperature from the air temperature.

The below equation applies to the calculation method of the wet bulb temperature :

1. Record the air temperature and rela-tive humidity.

2. Calculate the corresponding wet-bulb temperature using a psychrometric chart or table.

3. Find your VPD by subtracting the wet bulb temperature from the air temperature.

How to Calculate Leaf VPD

In order to work out the VPD of leaves you will need:

1. Leaf temperature (Tleaf)

2. Air temperature (Tair)

3. Relative humidity (RH)

When you have these numbers, you can then use the equation below to calculate actual leaf VPD:

VPD = eair-eleaf

Tips:

eair = saturation vapor pressure at air temperature (Tair)

eleaf = saturation vapor pressure at leaf temperature (Tleaf).

The saturated vapor pressure can also be approximated according to Antoine's equation.

VPD Calculator

Properly estimating VPD (Vapor Pressure Deficit) for maximizing indoor marijuana production is essential. This complex process has been made easier through the use of modern tools.

Features of VPD Calculators

Today’s VPD calculators have features that are incredibly helpful for the grower:

1. Easy Use Interface: Makes it easy to use and enjoy, quickly enter data.
2. Accurate Calculations: Provides precise VPD readings, a must when fine-tuning grow room environment.
3. Versatility: Grows in diverse growth-mediums, which makes it ideal for different grow systems.

Using a VPD Calculator

From here is extremely simple to get the ideal out of your vpd calculator.

If you want to use this tool, there are many online VPD calculators out there. A simple search on-line will point you in the direction of robust, easy to use calculators that will enable you too effectively control your grow room environment and nurture a happy heady weed plant.

Utilization of VPD

Understanding and utilizing Vapor Pressure Deficit (VPD) is crucial to optimizing the ideal growing place for your plants to thrive. The art is finding the sweet spot of what affects VPD to ensure optimum plant health and yield.

VPD Detection Equipment

Diverse equipment needs to be present if one wants to control/maintain VPD in an accurate way. These include:

• Hygrometers and Thermometers: To measure temperature and %RH.
• Data recorders and sensors: To be inserted into the environmental conditions (24 h per day/365 days per year) continuously.
• VPD Meters: Convenient to take in-the-field instantaneous readings.
• Software: For calculation of VPDs by means of temperature, relative humidity and pressure values.

Examples of such equipment include:

1. Decagon 5TM, EC5 Portable VPD Meter
2. Delta-T Introduces the VPD2 Evaporation and Transpiration Sensor
3. Rotronic HygroLog HLNT Data Logger with VPD Calculation
4. Extech RHT3 Hygro Thermometer with VPD

How Growers Can Affect and Modify VPD

There are a variety of ways in which growers can affect VPD within their grow rooms:

Way 1: Control the Temperature

Growers can have a huge impact on vapor pressure levels by controlling temperatures in their grow rooms. This, of course changes the VPD. HVAC systems like coolbot are a significant factor that helps to regulate temperature within a proper limit for perfect plant grow.

Way 2: Control the Humidity

Humidity control is another useful means of manipulating VPD. Depending on their crops’ needs, however, growers can use dehumidifiers to decrease humidity or humidifiers to add moisture. Manipulating humidity values allows you to strike that correct VPD balance for optimal plant growth.

Way 3: Adjust the Air Flow

Good air circulation in the grow area is important too. Air movement plays several roles, as it allows for the proper mechanics of vapor pressure deficit (VPD) with plants and also is essential for effective moisture distribution.

Way 4: Control the Light

Light has big impact on plant transpiration and VPD. The rate of plant transpiration, which significantly determines VPD, can be manipulated by regulating the intensity and duration of light.

Relationship between VPD and HVAC

Apart from the techniques described above, HVAC systems are also significant in VPD management. With an HVAC system, we can control the temperature and humidity quite accurately – it is important to VPD.

For instance, Altaqua Grow Room HVAC System – this has been designed to cater for specific temperature and humidity needs at different stages of plant growth. Featuring Siemens PLC control panels, it shows actual and target VPD so growers can program humidity and temperature thresholds.

Then the system is self adjusting to provide the perfect growing conditions. This tight control of VPD is a major feature of the Altaqua system and can guarantee that plants grow at their best condition.

How to Use VPD to Create the Perfect Growing Environment

Here are what should be considered with the different steps of having the best growing environment in terms of VPD:

By doing so, growers provide the optimum conditions not just for strong, healthy plant growth – but they also make it much harder for various crop problems to take hold.

Conclusion

Vapor Pressure Deficit (VPD) is a critical theory in cannabis growing and, more generally, the fundamental dynamics of plant growth. This important parameter prominently controls essential functions (e.g., transpiration, stomata operation, carbon dioxide (CO2) uptake, and nutrient absorption) in addition to the efficient management of plant stress.

Especially when you are growing indoor, with full control of the environment being such a fundamental requirement, knowledge and skilled steering of VPD becomes a focal point. With careful control of VPD, growers are able to increase crop health and performance dramatically. This is particularly important when in veg, as optimal VPD’s can make a dramatic difference during the vegetative (vpd for veg) phase of plant growth.

The flowering stage has own demands and fine-tuning the VPD in flower to optimal is key. For example, the optimal vpd for flower stage could be drastically different from veg and would require fine tuning for good results. An accurate VPD chart weed will be a great assistant for farmers to handle changing growth stages.

Also, with the help of some tools like VPD calculator it has become easy to get the sweet spot without making too many mistakes in different phases such as vegetation and flowering phase (flowering vpd). A well-designed flower of a VPD chart can help growers make good choices (base on the reversible transpiration effect) to keep their plants in a constant environment where they can flourish and grow sustainably.

The bottom line is that knowledge of what VPD is and how to put it into practice using modern tools like VPD charts and calculators gives growers the upper hand. They are able to lift their cultivation environments on-the-fly, depending on the unique requirements of cannabis plants at different growth stages. As such, VPD is a secret key to tapping into the full potential of cannabis plants and enabling successful plant growth.

FAQ on Vapor Pressure Deficit in Cannabis Cultivation

1. What is Vapor Pressure Deficit (VPD) in Plant Growing?

The Vapor Pressure Deficiency (VPD) in plant growing is a very important one and it corresponds the excessive moister of the air against its potential to hold moist in there. It is essential for distinctive plant interactions with their immediate atmosphere. In short, VPD is a measure of the ability of plants to draw in water and nutrients from the air which impacts on their general health and growth. For growers, especially those who grow in controlled-systems such as greenhouses, it’s critical to understand how VPD can be used to provide optimal growth conditions for the plant.

2. What Does VPD Do to Cannabis Plants?

VPD influences cannabis plants in terms of transpiration rate, stomata opening and nutrient absorption. Appropriate VPD levels provide efficient water and nutrient uptake, optimal photosynthesis and normal plant growth. Incorrect VPD values will cause problems such as dehydration, nutrient deficiencies and vulnerability to diseases like powdery mildew resulting in lower cannabis yield and quality.

3. What Is the Perfect VPD Range for Cannabis Plants?

The perfect VPD range for the cannabis plant is influenced by its stage of growth. Vapor Pressure Deficit (VPD), this is between 0.6-1.0 kPa in the seedling stage, typically speaking. During vegetative growth, optimal levels are 0.8-1.2kPa and during flowering keeping the VPD between 1.0-1.5k KPA is best. But these ranges can differ among strains and growing conditions.

4. How Do I Calculate VPD for My Grow Room?

You can figure out the VPD of your grow room with this formula: VPD = Saturation Vapor Pressure (SVP) – Actual Vapor Pressure (AVP). You need the air temperature and the relative humidity to calculate SVP and AVP. For convenience, even higher accuracy, these calculations can be made using online VPD calculators.