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Skyrocket Your Cannabis Yield: Optimal VPD for Veg Stage

For anyone involved in cannabis cultivation, understanding the VPD of cannabis at the veg stage can effectively help growers maximize the growth potential of their cannabis.

At the heart of VPD is the balance between temperature and humidity in the growing environment; if it is too high or too low, cannabis will suffer from growth stress. But when the optimal balance is found, cannabis can thrive, resulting in more yields and better quality. By fine-tuning the VPD, growers can create an environment for cannabis to efficiently absorb nutrients and thrive.

In this blog, we'll look at VPD for veg of cannabis.

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The Role of VPD in the Cannabis Veg Stage

The growing season is a critical time for cannabis, and VPD directly affects a number of cannabis growth factors, including root health, stem strength, leaf development, and nutrient uptake. If the right VPD is consistently maintained, cannabis will be able to fulfill its mission of growing taller and bigger during the growing period.

Next, we'll look at how VPD plays an active role in all aspects of cannabis growth.

VPD and Root System Health

Having a large root system allows cannabis to grow in abundance. When cannabis is in the optimal range of VPD for veg, the roots have access to sufficient water and oxygen, which in turn promotes root expansion and branching, enabling cannabis plants to grow taller and larger during the growth cycle rapidly. On the other hand, proper VPD levels for veg can help maintain soil moisture and aeration, preventing root diseases such as rot and root problems caused by lack of oxygen.

At the same time, plants with healthy root systems are usually more resistant to various pests, diseases, and environmental stresses.

Effects on Stem Strength and Thickness

A healthy root system leads to strong stalks. Optimal VPD for veg levels favor the proper flow of water through the cannabis body, which in turn strengthens the stalks, making them thicker and more resilient. Stronger stalks can better support the buds' weight during the flowering stage, reducing the risk of plant damage or collapse.

Influence on Leaf Development and Size

Leaves are the primary site of photosynthesis, where plants convert light into energy. Optimal VPD for veg maximizes stomata (tiny openings in the leaf). This allows for maximum photosynthesis and promotes healthy leaf development, resulting in larger, more robust leaves. Larger leaves capture more light to power cannabis growth.

Appropriate VPD for veg levels can regulate leaf stomatal openness, which promotes CO2 uptake and improves photosynthetic efficiency while avoiding excessive water loss.

VPD's Effect on Nutrient Uptake Efficiency

Optimal VPD for veg levels increase cannabis's ability to absorb water and nutrients from the soil. When at optimal VPD for veg, cannabis transpires at an optimal rate, which creates a pulling force that promotes the upward transport of water and nutrients absorbed by the roots. It also maintains the water transport system in the leaves and stems, promoting balanced cannabis growth.

Influence on Overall Plant Vigor and Resilience

VPD not only affects specific aspects of cannabis growth but also helps to improve the overall vigor and resilience of the plant. Proper VPD for veg creates an environment for cannabis to thrive, making it more resilient to stressors such as pests, disease, and environmental fluctuations.

Strong, healthy cannabis is more capable of recovering from stress and continuing to grow vigorously. Cannabis, with this resilience, is better able to achieve high yields and maintain the quality of the final product.

Throughout the cannabis growing period, proper VPD promotes a strong root system, helping stems and leaves thrive. It also maintains efficient nutrient uptake and the overall vigor of the cannabis. By keeping optimal VPD levels, growers can build a strong foundation for successful flowering and abundant cannabis production.


Ideal VPD Range of Cannabis Vegetative Stage

Based on the previous subsection, we know that maintaining the correct VPD during the growing period promotes all aspects of cannabis growth, so what is the right VPD for veg?

Determining the Optimal VPD Range for The Veg Stage

Each grower has his or her own preferences and is faced with many variables that may affect the optimal climate. Generally accepted VPD ranges exist to achieve the desired quality, yield, odor, potency, and color. Such as:

The optimal VPD for veg stage of cannabis is usually between 0.8 and 1.2 kPa (kilopascals).

This range balances the relationship between temperature and humidity, and cannabis can transpirate efficiently without too much stress. Cannabis within this VPD range can thrive by absorbing water and nutrients efficiently while minimizing the risk of pests and diseases.

If a grower needs to determine the exact VPD range appropriate for a particular strain and growing conditions, they can start with the recommended range and then make adjustments based on how the cannabis responds. During this process, growers will need to observe the growth patterns, leaf appearance, and overall vigor of the cannabis, fine-tuning the VPD to meet the needs of the cannabis plant based on the actual cannabis conditions.

Temperature and Humidity Settings for Optimal VPD

Temperature and humidity levels should be adjusted at each stage of cannabis cultivation, as cannabis has changing needs as it matures. Adjustments at each stage of cultivation do not require the grower to set a static climate; rather, the conditions of the growing environment need to be adapted to the needs of the cannabis as it moves from one stage to another.

Achieving the desired VPD for veg values requires a careful balance of temperature and humidity. Below are general guidelines for temperature and humidity settings during the asexual reproduction phase:

Relative Humidity: 40-70% (decrease by 5% per week)

Temperature: 71-82 °F (22-28 °C) with lights on / 64-75 °F (17-23 °C) with lights off

Adjusting these parameters can achieve the desired VPD for veg stage. For a daytime temperature of 78 °F (25.5 °C) and a humidity level of around 60%, the optimum VPD value would be approximately 1.0 kPa.


Comparing VPD Needs in Seedling vs. Veg Stages

The VPD requirements of the cannabis plant differ between the seedling stage and the Veg stage:

Seedling stage: The optimal VPD range for seedlings is usually low, around 0.4-0.8 kPa.

Veg stage: When the plant enters the Veg stage, its VPD requirement will shift to 0.8-1.2 kPa.

Seedlings are more sensitive to environmental conditions and require higher humidity to prevent excessive transpiration and stress. This can be achieved by maintaining high humidity (60-70%) and slightly lower temperatures (68-77°F or 20-25°C).

In turn, the change in VPD required from seedling to growing stage can reflect the plant's increased ability to handle transpiration and the need for more efficient nutrient uptake to support rapid growth.

Seasonal Variations and Adjustments

Growers constantly adjust their VPD during the different stages of cannabis cultivation, and they also need to be aware of the need to adjust their VPD accordingly during the different seasons. Seasonal changes can significantly impact the temperature and humidity levels in the growing environment, so it's necessary to make adjustments according to the different seasons in order to maintain an ideal VPD.

WINTER: Indoor grow spaces may become cooler and drier. To compensate, growers may need to use humidifiers to increase humidity levels and heaters to raise temperatures slightly to maintain an optimal VPD range.

SUMMER: Higher outdoor temperatures will increase indoor temperatures, which may decrease relative humidity. Growers can keep the temperature and humidity within the desired range by using air conditioners and dehumidifiers.

At the same time, the use of reliable temperature and humidity control equipment and real-time monitoring systems can make these adjustments more accurate and easier to manage.

Analyzing the Risks of Improper VPD Levels in Veg Stage

Being at an inappropriate VPD for veg for an extended period of time can lead to a variety of problems that can affect cannabis health and yield. This section will explore the symptoms of an imbalanced VPD for veg, the effects on cannabis health and yield, and the long-term consequences of inappropriate VPD levels.

Symptoms of VPD Imbalance in Cannabis Veg Stage

Identifying the symptoms of VPD for veg imbalance early can help growers take corrective measures before the plants suffer severe damage. Here are the key symptoms to watch for:

Root Odour and Decay

Too low a VPD for veg can lead to root health problems such as root rot or poor root development. When VPD is too low, too much water can build up in the growing medium, causing a lack of oxygen in the root system and promoting fungal growth. When the root system is damaged or infected with pathogens, this can lead to root rot and odors.

Conversely, if the VPD for veg is too high, it may cause soil moisture to evaporate too quickly and the soil to dry out. Dry soil limits root expansion and new root growth, which reduces the area and capacity of the root system to absorb. The root system may weaken or even dry out in severe cases, compromising its normal function.

Soft and Limp Stems

Stem weakness is often a sign that the VPD for veg is out of balance.

If the VPD for veg is too low, the water inside the cannabis cannot evaporate efficiently, which can lead to waterlogged stem tissues and weak stalks. This can make the plant more susceptible to physical damage and less able to hold the weight of future buds.

If the VPD for veg is too high, it can cause the cannabis to evaporate water too quickly, and with an insufficient supply of water, the stalks may become soft and weak, and the overall plant may look shriveled.

The cell walls of the stem may become fragile over a long period of time at improper VPD levels. This causes the stem to break or damage easily, affecting the overall structure and stability of the cannabis.


Leaf Curling and Wilting

Leaves are very sensitive to changes in VPD. When the VPD for veg is too high, the leaves curl and wilt due to excessive water loss. This is a protective response by cannabis trying to reduce transpiration.

However, if the VPD for veg is too low, the leaves may overstretch and eventually wilt due to waterlogging. Alternatively, the root system may become damaged due to insufficient oxygen supply to the roots, which affects nutrient uptake, leading to yellowing or spotting of the leaves.

Both conditions, too high or too low VPD, can seriously affect photosynthesis and the plant's overall health.

Reduced Photosynthesis Efficiency

The efficiency of photosynthesis is closely related to the ability of plants to regulate water and gas exchange through stomata. Inappropriate VPD can cause stomatal dysfunction, leading to reduced photosynthesis.

For example, when cannabis has a high VPD for veg, stomata close to reduce water loss, resulting in reduced carbon dioxide uptake and less efficient photosynthesis. When cannabis has a low VPD for veg, stomata may open excessively, leading to excessive water uptake and evaporation, potentially causing a water and nutrient imbalance. Both of these conditions can reduce the amount of energy needed for growth and development, ultimately stunting the plant's growth.

Stunted Growth and Development

When VPD for veg is not optimal, plants may exhibit stunted growth and poor development. This can manifest as smaller leaves, shorter internodes, and a lack of vigor. Stunted growth directly impacts the plant's ability to reach its full potential during the flowering stage.

Nutrient Deficiencies and Toxicities

An imbalance in VPD for veg can disrupt nutrient uptake by the plant.

When VPD for veg is too high, marijuana reduces water evaporation due to insufficient water, which can lead to higher salt concentrations in the soil. High salts can inhibit nutrient uptake by the root system, leading to nutrient toxicity.

When the VPD for veg is too low, too much water may lead to excess nutrient accumulation in the soil and excessive nutrient uptake by the root system, leading to nutrient toxicity. Common symptoms include leaf edge burning, leaf discoloration, and growth stagnation.


Increased Susceptibility to Diseases

Plants are more susceptible to disease under the stress of an out-of-phase VPD.

When in high VPD for veg, stomata close, and the leaf surface becomes dry. This weakens the plant's natural defence mechanisms; on the other hand, the leaves become dry or curled due to water loss, making them susceptible to mechanical damage and providing an entry point for pathogen invasion.

When cannabis has low VPD for veg, its cells are over-swollen, and the tissues are fragile and susceptible to pathogen infestation. At the same time, leaf stomata remain open for extended periods of time, and the leaf surface is moist, providing an ideal environment for pathogens (e.g., fungi and bacteria) to colonize.

Impact On Plant Health and Yield

The negative effects of improper VPD levels extend beyond immediate symptoms. They can have lasting impacts on plant health and yield.

Flowering and Yield Issues

Inappropriate VPD during the asexual reproduction stage can delay or interfere with the flowering process.

Plants that have been under inappropriate levels of VPD for a long period of time may grow fewer and smaller buds or produce loose and less dense flowers. This will likely lead to inconsistent flowering, with individuals in a cannabis population flowering at unsynchronised times. All of this can affect the final quality of the flowers.

Decreased Quality of Final Product

The quality of the final cannabis product is directly affected by the plant's health throughout its life cycle. Inappropriate VPD can reduce cannabinoid and terpene levels, negatively impacting harvested buds' potency, flavor, and aroma.

For example, when cannabis is chronically at a high VPD, a lack of moisture can lead to a reduction in cannabis secondary metabolites, which can affect the aroma and flavor of the cannabis, ultimately resulting in a product that may lack a strong aroma and distinctive flavor.

Another example is that when cannabis is at low VPD for a long period of time, the humid environment is prone to mold and bacteria. High humidity increases drying time, making it more susceptible to mold and disease during preservation, affecting the longevity and quality of the product.

Long-term Soil and Environmental Impact

Prolonged periods of inappropriate VPD for cannabis can not only affect the health and yield of the plant itself but also negatively impact the soil and growing environment.

Frequent watering may lead to the accumulation of nutrients, especially salts, in the soil. At the same time, heavy watering may result in nutrients being washed out of the soil, thus reducing soil fertility, which is not conducive to sustainable cultivation.

Improper VPD levels can negatively affect plant health and yield in a number of ways, such as leading to root health problems, stem weakness, leaf curling, and reduced photosynthetic efficiency. They can also affect flowering and yield, and ultimately product quality, as well as long-term soil and environmental impacts.

Monitoring and Adjusting VPD in the Vegetative Stage

Maintaining proper VPD during the growing period is crucial. For this reason, growers need to not only detect VPD levels during the growing period but also constantly adjust the growing environment to achieve optimal VPD levels.


Using Hygrometers and Thermometers

Hygrometers and thermometers are essential tools for monitoring VPD. A hygrometer measures the growth room's relative humidity (RH), while a thermometer tracks the temperature. Together, these devices provide the necessary data to calculate VPD.

To use these tools effectively, growers need to place multiple hygrometers and thermometers at different heights and locations in the grow space to get accurate readings of the environment.

It is important to note that sensors should not be placed directly under lights or near ventilation ducts to avoid biased readings. Growers also need to check and record readings regularly to monitor changes and trends in temperature and humidity.

Real-time Data Logging and Analysis

In addition to taking readings with thermometers and hygrometers, growers can continuously track temperature and humidity levels through the use of digital sensors connected to a central monitoring system. Real-time data logging and analysis provide a more advanced method of monitoring VPD.

Digital sensors provide a constant stream of data, making it easy for growers to monitor data while greatly reducing labor costs. Most digital sensors can be set up with alarms to alert and notify the grower when VPD is outside of the expected range so that corrective action can be taken in a timely manner. This allows the grower to be the first to notice any deviation from the optimal VPD range.

Interpreting VPD Data for Optimal Adjustments

Interpreting VPD data requires understanding the relationship between temperature, humidity, and VPD. By using the data collected to calculate VPD, growers can adjust to optimize the growing environment.

Steps for adjusting the VPD:


Specific operational content

Calculating VPD

Determine the current VPD from temperature and humidity readings using a formula or online VPD calculator

Analysing trends

Look for trends in the data to understand the impact of environmental factors on VPD over time

Carry out adjustments

Adjustment of temperature and humidity levels using HVAC systems, humidifiers, dehumidifiers, or ventilation equipment

Observing Plant Responses

In addition to regularly monitoring equipment, growers can check that the VPD is within the optimal range by observing the state of cannabis phenology and growth patterns.

Cannabis can be observed for leaf appearance, stem strength, and growth patterns. Healthy cannabis is usually vibrant and vigorous, while signs of an imbalance in VPD include curled, wilted, or discolored leaves. Sturdy stalks indicate that cannabis has proper VPD, while weak stalks may be problematic. Consistent, vigorous growth indicates that the plant's VPD is properly controlled, while stunted or irregular growth suggests VPD problems.

Regular Calibration and Maintenance of Equipment

Apart from the choice of equipment, maintenance of the equipment also needs attention. Growers need to gently wipe the thermometer and hygrometer with a clean cloth regularly to avoid dust and dirt build-up that can affect the accuracy of the readings. It is also important to keep the sensors clean and free of dust and debris.

It is important to note that you also need to check your device's battery level regularly. A low battery level may result in inaccurate readings. In addition, check the device regularly for signs of wear and tear. If there is wear and tear, faulty parts need to be replaced promptly, which helps maintain the monitoring system's integrity.

During the asexual growth phase of cannabis, growers can monitor environmental conditions through the use of hygrometers and thermometers. By recording real-time data, combined with an accurate interpretation of the VPD, growers can better understand the needs of their cannabis.

At the same time, by observing how cannabis responds to changes in the environment and by regularly maintaining the equipment, growers can help create a more suitable growing environment for cannabis.

These measures can help improve the quality and yield of cannabis growth, and while they don't completely guarantee that optimal growing conditions will be achieved, they are important steps toward that goal.

Achieving Optimal VPD with Altaqua HVAC System

While effective, traditional methods using hygrometers and thermometers require constant manual monitoring and adjustments. The Altaqua HVAC system offers a more advanced, convenient, and efficient solution.

Compared to traditional methods, the Altaqua system helps growers maintain ideal VPD by controlling dew points, utilizing intelligent automation, and providing a redundant and scalable design.


Dew Point Control

Altaqua HVAC System uses dew point control instead of RH to provide more consistent humidity readings.

A large number of grow lights are present in the grow room, and the temperature of the grow room changes frequently due to the lights, which can also change the RH level frequently. Conventional hygrometers may cause errors in the data due to the influence of temperature. The dew point is independent of temperature and remains stable to represent actual humidity accurately. Accurate humidity data enables the calculation of an accurate VPD.

On the one hand, the use of dew point control effectively maintains a constant humidity level and avoids drastic fluctuations in humidity caused by temperature changes. On the other hand, the Altaqua HVAC System prevents condensation from forming on plant and equipment surfaces by effectively controlling the dew point. Mold is a common problem in cannabis cultivation and can lead to reduced crop yields. While traditional relative humidity control tends to form condensation when the temperature plummets, dew point control effectively avoids this problem. Dewpoint management reduces the risk of mold, keeping cannabis healthy and the grow room environment stable.

In addition, efficient dew point control helps reduce energy consumption by avoiding excessive heating or cooling, and Altaqua's system is not only efficient but also economical. The Altaqua HVAC System is not only efficient but also economical, allowing growers to maintain an optimal environment without incurring high energy costs.

Intelligent Automation

Traditional methods of measuring VPD require multiple thermometers and hygrometers to be placed around the grow room and manually recorded and analyzed. This is extremely time-consuming and labor-intensive.

The Altaqua HVAC system uses Siemens PLC control with customized software to measure VPD efficiently. The Siemens PLC control panel displays the current VPD and target VPD, allowing the grower to visualize the room's VPD level. Simply set the desired combination of humidity and temperature targets, and the Altaqua system does the rest to create the ideal growing environment.

Additionally, growers can set specific parameters for different stages of plant growth (e.g., seedling stage, growing stage, etc.), and the Altaqua HVAC System automatically switches between different control modes depending on the stage of plant growth. For example, during the growing stage, higher humidity and slightly lower temperatures can be set, and the Altaqua HVAC System can automatically adjust to these settings to ensure that the environment is always in line with the plant's needs.

Redundant and Scalable Design

Conventional testing equipment can fail, leading to serious disruptions. the Altaqua HVAC system utilizes a redundant and scalable design with multi-stage circuits and compressors, and the consolidation of multiple independent sub-systems ensures seamless operation and an uninterrupted cultivation environment, even in the face of individual system failures.

Whether it's a small grow room or a large cultivation facility, when it's time to scale up, traditional methods require manual expansion, which is labor-intensive and error-prone. The Altaqua control system supports the addition of new sensors and controls that can be easily scaled up as your business grows, ensuring continuous optimal VPD control without the need for extensive manual adjustment.

Altaqua air conditioning systems are carefully designed to provide accurate humidity and temperature control by regulating air and moisture levels in indoor areas. They can meet the unique requirements of cannabis cultivation and optimize the environment for cannabis growth.

Altaqua HVAC systems are competitively low in total cost of ownership, ultra-long-life equipment, and a holistic, carefully crafted solution that ensures unrivaled growing conditions. Our experienced engineering team is ready to provide customized solutions for your unique needs. Simply explore more information on our website and contact our dedicated team of consultants.


Understanding VPD during the growth phase of cannabis and maintaining it at appropriate levels promotes healthy root systems, robust stem development, improved plant nutrient uptake efficiency, and overall vigor.

Traditional methods such as hygrometers and thermometers provide a basic way to monitor VPD but require constant manual manipulation and adjustment. By regularly calibrating and maintaining these tools, growers can ensure their accuracy and reliability. This method is time-consuming and prone to human error. Due to delayed response, it may also deviate from the optimal VPD. Therefore, it is difficult to maintain stable growing conditions.

The Altaqua HVAC system solves these challenges by providing a more advanced, automated, and reliable solution for VPD control. With features such as precise dew point control, intelligent automation for real-time adjustments, and a redundant and scalable design, the Altaqua system provides a seamless and efficient way to maintain optimal growing conditions. This state-of-the-art system reduces the manual labor required to monitor and regulate VPD and ensures a stable environment that supports healthy plant growth and maximizes yields.

Incorporating the Altaqua HVAC system into your cannabis cultivation setup can dramatically improve the efficiency and success of your growing operations. Growers can use its advanced features to ensure that their plants receive the best possible care, resulting in higher yields and better-quality products. As you continue to improve your cultivation techniques, investing in reliable technology, such as the Altaqua HVAC system, will go a long way toward helping you achieve your cultivation goals.


1. What is the optimal VPD range for cannabis during the asexual growth phase?

The optimal VPD range for cannabis during the asexual growth phase is usually between 0.8 and 1.2 kilopascals (kPa). This range ensures the plant transpires efficiently, supporting nutrient and water uptake while minimizing stress. Keeping VPD within this range helps maintain healthy growth, strong stems, and vigorous leaf development, which is critical for a successful transition to flowering.

2. How does improper VPD affect cannabis growth in the asexual reproduction phase?

Inappropriate VPD levels can lead to several problems for cannabis during the asexual growth phase. Too high a VPD can lead to excessive transpiration, resulting in water stress, nutrient deficiencies, and reduced photosynthetic efficiency. Too low a VPD can lead to water logging, which promotes mildew and root rot and reduces nutrient uptake. Both of these extremes can stunt growth, weaken stems, and reduce overall plant vigor, affecting the final product's yield and quality.

3. What tools can I use to monitor and adjust the VPD of my cannabis?

To monitor and adjust VPD, you can use hygrometers and thermometers to measure relative humidity and temperature. For more advanced monitoring, real-time data loggers and automated HVAC systems, such as the Altaqua HVAC system, can continuously track and adjust these parameters. These tools help maintain optimal VPD ranges by making precise real-time adjustments based on current conditions.

4. Why is dew point control important for managing VPD?

Dew point control is critical to managing VPD because it prevents condensation and ensures stable humidity levels. By controlling the dew point, you can avoid high humidity levels that can lead to mold growth and ensure that the air is not too dry, which can stress the plants. systems such as Altaqua HVAC systems provide precise dew point control to help maintain the optimal environment for cannabis cultivation.

5. What are the benefits of using intelligent automation for VPD control in cannabis cultivation?

Intelligent automation for VPD control offers several advantages in cannabis cultivation. It continuously monitors environmental conditions and makes real-time adjustments to maintain optimal VPD levels, reducing the need for manual monitoring and adjustments and minimizing human error. The automation system can also be customized for different growth stages, ensuring that plants receive the best possible care throughout their life cycle. In short, smart automation improves the efficiency, consistency, and quality of cannabis production.

6. What are the signs that a cannabis plant is experiencing VPD irregularities?

Signs that a cannabis plant has abnormal VPD include:

Curled and wilted leaves: High VPD can lead to excessive water loss, while low VPD can lead to water logging.

Stunted growth: Smaller leaves, shorter internodes, and lack of vigor indicate poor VPD control.

Nutrient deficiencies and toxicity: An imbalance in VPD disrupts nutrient uptake, leading to symptoms such as leaf margin burn or discoloration.

Increased susceptibility to disease: Both high and low levels of VPD can weaken a plant's natural defenses, making it more susceptible to pathogens.

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