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Uncover your target VPD for veg and elevate your grow

Tom Starley
March 28, 2024
10 min read
A grower who has successfully targeted the right VPD for veg. Their target VPD for veg is on point and the plants look healthy.
A grower who has successfully targeted the right VPD for veg. Their target VPD for veg is on point and the plants look healthy.
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Welcome back to our mini-series on mastering Vapor Pressure Deficit (VPD) for cannabis cultivation. Our previous piece delved into the optimal VPD ranges for the delicate seedling stage, setting the foundation for healthy plant growth. 

Today, we're elevating your grow knowledge by uncovering the target VPD for the vegetative (veg) stage, a crucial period where your cannabis plants grow stems and leaves in preparation for flowering.

Understanding the ideal VPD for veg is pivotal for any indoor growers aiming to grow the best plants. Your plants demand precise environmental conditions in the vegetative stage. 

Humidity and temperature need to be in perfect harmony to stay within the optimal VPD range. This balance ensures your plants can effectively transpire, take up essential nutrients, and thrive.

So, whether you're a seasoned cultivator or just starting your growing journey, understanding the target VPD for veg is key to unlocking the full potential of your cannabis plants. So, let's dive and elevate your grow!

Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so in accordance with the law and subject to appropriate permissions and licenses of the applicable country.

A cannabis plant that likes target VPD for veg that is quite low.

Understanding VPD in the vegetative stage

Diving into the vegetative phase of cannabis cultivation, the concept of vapour pressure deficit emerges as a cornerstone for producing robust and healthy plants. But what exactly is VPD, and why does it hold such weight in the veg stage of growth?

What’s vapour pressure deficit about?

At its core, VPD is the difference between the amount of moisture in the air and how much moisture it can hold when it's saturated

It's essentially a measure of the driving force behind plant transpiration - the process through which your plants release water vapour into the air from their leaves. 

An optimal VPD range for veg creates an environment that encourages your plants to transpire at a rate favourable for vigorous growth, ensuring they efficiently take up water and essential nutrients from the root zone.

An illustration showing the target VPD for veg and the other stages of growth.

Targeting the ideal VPD for vegetative plant growth

The best VPD for veg stage cannabis plants typically falls within a range that balances the air temperature and relative humidity to promote healthy transpiration without causing undue stress. 

This optimal range is often depicted in a veg VPD chart, serving as a handy reference for growers. 

Achieving a good VPD for veg requires a keen eye on your grow room's conditions, adjusting temperature and humidity setpoints as needed to maintain this delicate balance.

The impact of VPD on plants cannot be overstated. It directly influences leaf temperature, water vapour release, and, by extension, nutrient uptake and overall plant health. 

A consistent vapour pressure deficit ensures that your plants are neither overburdened with excessive transpiration or stifled by inadequate moisture release, which can hamper vegetative growth.

An illustration showing the target VPD for veg and the effects it has in the grow room.

What should VPD be during veg?

During the vegetative stage of cannabis growth, the ideal Vapor Pressure Deficit (VPD) should be between 0.7 and 1.0 kPa (kilopascals). 

This range helps ensure that your cannabis plants can effectively transpire, which is crucial for their uptake of water and nutrients. 

Keeping VPD in this sweet spot supports optimal plant health and prepares them for a successful flowering stage.

VPD is about more than just temperature and relative humidity

Creating the perfect VPD ranges for your veg stage plants involves more than just monitoring the ambient room temperature and relative humidity. 

Factors like leaf temperature, light intensity, and the presence of carbon dioxide also play pivotal roles in how your plants respond to their environment. 

For instance, higher light intensities can increase leaf temperature and, consequently, the plant's transpiration rate, necessitating adjustments to VPD parameters to keep growth on track.

Understanding and managing VPD during the vegetative stage is about creating an environment where your cannabis plants can thrive. 

By targeting the ideal VPD for veg, monitoring vital environmental factors, and making adjustments as needed, you can ensure your plants have everything they need and prepare them for a successful flowering stage.

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VPD calculator

The science behind VPD and vegetative growth

The vegetative stage of cannabis cultivation is a critical period where the foundation for healthy, fruitful plants is built. But to truly optimise your grow, a deeper understanding of the science behind VPD and its role in vegetative growth is essential.

VPD's role in plant transpiration and nutrient uptake

Transpiration is the process by which plants release water vapour from their leaves into the surrounding environment. This vital function cools the plant whilst facilitating the uptake of nutrients from the soil. 

The efficiency of this process is heavily influenced by VPD, which dictates how much moisture the air around the plant can hold. 

When VPD is within the ideal range for the veg stage, it creates the perfect conditions for transpiration, promoting vigorous plant growth and enhancing nutrient absorption.

Balancing relative humidity and temperature for optimal VPD

Achieving the optimal VPD for veg is challenging. But, maintaining this balance ensures that the air around a cannabis plant has just the right amount of moisture to support transpiration without causing plant stress or dehydration. 

Here, a VPD chart for veg becomes an invaluable tool, offering a visual guide to the perfect temperature and humidity setpoints based on your grow room's current conditions.

However, VPD isn’t just about hitting a target on a chart. 

The unique characteristics of your grow room, including air circulation, light intensity, and CO2 supplementation, can all influence how you should adjust your environment to maintain the ideal VPD range. 

For example, as plants transpire and release moisture, they also cool down, which can affect the temperature of your plant’s leaves and the overall VPD in your grow space.

Understanding the interplay between vapour pressure deficit, plant transpiration, and nutrient uptake allows you to fine-tune your environment to support healthy and robust vegetative growth. 

This sets the stage for an abundant flowering phase and ensures that your plants are as healthy as possible.

Consequences of suboptimal VPD in the vegetative stage

While understanding the ideal VPD for veg is crucial, it's equally important to recognise the potential implications when cannabis plants in veg are subjected to less than ideal VPD levels. 

The delicate balance of vapour pressure deficit can significantly influence plant health, and deviations from the ideal range can lead to a host of issues.

A cannabis plant in veg that is on a low VPD environment.

If veg stage VPD is too low

Low VPD indicates high relative humidity and low temperature. Cannabis plants may experience reduced transpiration rates. 

If veg stage VPD is too high

Higher VPD results from low relative humidity and high temperatures, which can cause plants to transpire excessively and result in too much water loss. 

A study found that drastic fluctuations in VPD led to “decreased stomatal conductance, CO2 assimilation rate, and biomass production in lettuce.” This shows that significant VPD changes can negatively impact indoor plant growth. 

The study emphasised the importance of stable environmental control in greenhouses for better plant growth and yield. 

Stress and stunted growth

Unmanaged VPD Vapor Pressure Deficit during the vegetative growth stage can lead to plant stress and stunted growth. When VPD levels are too high or too low, it disrupts the plant's ability to transpire properly and exchange gases, resulting in inadequate nutrient and water uptake. 

This imbalance can hinder the plant's development, leading to smaller plants and reduced yields. Monitoring and adjusting VPD levels to support healthy plant growth is crucial. 

Risk of nutrient imbalances

Suboptimal VPD during vegetative growth can lead to nutrient imbalances, including deficiencies and toxicities, by affecting the plant's ability to transpire and absorb nutrients efficiently. 

Improper VPD levels can disrupt water and nutrient uptake, leading to either nutrient scarcity or excess within the plant tissues. This imbalance can significantly impact plant health and growth.

Susceptibility to pests and diseases

Unmanaged VPD during the vegetative growth phase can increase a plant's susceptibility to various pests and diseases. 

Inappropriate VPD levels can weaken plant defences, making them more vulnerable. Common issues include fungal diseases like powdery mildew, root rot or bud rot, and pests like spider mites and aphids

Maintaining optimal VPD helps ensure plants are more resilient and less likely to encounter these problems. 

Download your FREE 
VPD calculator

Troubleshooting VPD issues in the vegetative stage

When troubleshooting, identifying and correcting common VPD-related problems is vital to ensuring your plants thrive and reach their full potential.

A cannabis plant that is in a low VPD environment meaning it has become susceptible to mould.

Identifying common VPD problems

The first step is recognising the signs that your VPD might be off. The following symptoms can all indicate VPD issues. 

  • Drooping leaves
  • Slow growth
  • The appearance of fungal diseases 

Keeping a close eye on leaf temps can provide insights, as it's directly affected by transpiration rates and the surrounding VPD. 

If the temperature of your leaves is too low, it might suggest high relative humidity and low air temperature, while high leaf temperatures could indicate the opposite.

Adjusting your grow room's environment

Once you've identified a potential VPD issue, the next step is to adjust your grow room's environmental conditions. Here's how:

Humidity 

If your VPD is too high, increasing the humidity level can help. This can be achieved by using a humidifier or adjusting your grow room's ventilation. 

On the flip side, if your VPD is too low, reducing humidity with a dehumidifier or increased ventilation can help bring your VPD back into the optimal range.

Air temperature

Adjusting the air temperature is another effective way to correct VPD issues. If the air is too warm, causing a high VPD, cooling the environment can help. 

This might involve adjusting your grow room's air conditioning settings or increasing airflow. If the air is too cold, raising the temperature with heaters or reducing ventilation can help balance the if the air is too cold VPD.

An illustration showing how the target VPD for veg also effects leaf surface temperature.

Monitoring leaf temperature

Leaf temperature plays a crucial role in leaf VPD and can be influenced by environmental factors like air temperature and humidity. 

Using infrared thermometers or thermal cameras to take a temperature reading can help you monitor leaf temperatures and leaf VPD directly. Then, you can make more informed decisions about adjusting your grow room's conditions.

By carefully monitoring and adjusting humidity, air temps, and leaf temperature, you can maintain an ideal VPD for your cannabis plants in the vegetative stage and beyond. 

This proactive VPD management approach ensures that plants can transpire effectively and uptake nutrients efficiently. Ultimately, strong vegetative growth leads to healthier plants.

Remember, every grow room is unique, and what works for one setup may not work for another. 

It's important to experiment and adjust your approach based on the specific needs of your plants and the nuances of your growing environment. 

Maintaining the ideal VPD for veg is not just about preventing problems; it's about creating an environment where your cannabis plants can flourish.

By closely monitoring and adjusting your grow room's humidity and temperature, you can ensure your plants enjoy a healthy vegetative stage, setting the stage for a successful transition to flowering and, ultimately, a top-quality harvest.

Get your target VPD for veg now and download your free VPD chart.

Veg VPD chart: Your visual guide 

Getting the hang of the optimal vapour pressure deficit for your plants during the vegetative stage is more straightforward with VPD charts specifically designed for this crucial phase. 

It’s a vital tool for growers, ensuring the ideal balance between ambient temperature and humidity is achieved, creating an environment where cannabis plants can thrive.

VPDs charts serve as a detailed guide, pinpointing the perfect VPD range for the vegetative stage, typically around 0.7 to 1.0 kPa. 

By comparing your grow room's current temperature and humidity levels against the chart, you can determine if your setup aligns with the optimal conditions for vegetative growth.

This immediate feedback allows for swift adjustments to your grow room's climate, keeping your plants in their optimal growth conditions. 

Incorporating VPD charts into your daily grow routine can greatly improves your ability to fine-tune your environment.

Make it a habit to compare your climate controls against the chart's recommendations, particularly after any changes to your grow space, like alterations in lighting or airflow.

Adopting this proactive strategy ensures your plants receive the best conditions during their vegetative stage, setting a solid foundation for their subsequent flowering phase.

With the VPD chart as a cornerstone of your growing practices, you're well-equipped to nurture your plants through their vegetative growth.

The Grow Sensor and IOS Android App.

Monitoring and managing VPD with technology

By now, you know that maintaining the perfect vapour pressure deficit is essential for ensuring your plants flourish. 

While basic tools like hygrometers and thermometers can serve beginners well by providing fundamental temperature and humidity readings, those committed to elevating their grow should consider advanced technology. 

Enter the Grow Sensor, a game-changer in precision environment monitoring.

Use the Grow Sensor to manage your VPD

Choosing the right equipment to monitor VPD ranges can drastically impact the health and productivity of your cannabis plants. 

The Grow Sensor is an advanced tool designed to provide comprehensive environmental data. 

Positioned at the canopy level, it offers a detailed analysis of the conditions directly affecting your plants. 

This includes temperature and relative humidity and more sophisticated measurements like VPD calculated with precision.

Additional features tailored for cannabis cultivation

CO2 measurement

Tracks CO2 levels, which are crucial for photosynthesis.

Continuous light measurement

Equipped with PPFD and full-spectrum PAR sensors, it ensures your plants receive the optimal light for growth.

Daily Light Integral (DLI) Capability

Monitors the total amount of light your plants daily day, essential for vegetative growth.

Leaf surface temperature sensing

Along with leaf VPD calculations, measuring LST provides insights into the microclimate around your plants' leaves.

Dew point tracking and soil analysis

Offers a holistic view of your grow environment, including optional probes for soil EC, moisture, and temperature.

Support for photoperiods

Adapts to your plants' day and night cycles, providing tailored data.

Robust connectivity and data logging

With long-range Wi-Fi and offline logging, you're always in the loop about your grow room conditions.

The Grow Sensor isn't just about data collection; it's about enabling precise environmental control. 

Its user-friendly app, compatible with iOS, Android, and soon, desktop platforms, sends customisable alerts and provides real-time information. 

This ensures you can adjust your grow room's conditions with pinpoint accuracy. Maintaining the ideal VPD for the vegetative stage and setting the stage for maximum plant growth and health.

Incorporating technology like the Grow Sensor into your grow room setup means embracing a proactive approach to cannabis cultivation. 

Ensure your plants have the perfect conditions to thrive, with every aspect of their environment monitored and managed precisely. 

Whether you're a seasoned grower or just starting, understanding and implementing advanced VPD management tools like the Grow Sensor can significantly elevate the health and yield of your cannabis crop.

The graphs page on the Grow Sensor app showing target VPD.

Takeaways

Cannabis cultivation brings its own set of challenges and learning curves, particularly when it comes to creating the ideal environment for your plants. 

This article explored the pivotal role of vapour pressure deficit in the vegetative stage, uncovering its critical impact on plant health, growth, and productivity. 

Understanding and managing VPD is more than a cultivation practice; it's a science that, when mastered, can significantly enhance the quality and yield of your plants.

The ideal VPD for veg (0.7 to 1.0 kPa) sets the stage for vigorous plant growth, ensuring that your plants thrive in an environment tailored to their needs. 

Embracing technology, such as the Grow Sensor, offers a modern solution to age-old cultivation challenges. 

This advanced tool simplifies monitoring VPD andalso provides a comprehensive overview of your grow room's conditions, ensuring that your plants are consistently nurtured in an ideal environment.

As we conclude this segment of our mini-series on VPD across different stages of cannabis growth, it's clear that the key to successful cultivation lies in precision, knowledge, and the right tools. 

From novice indoor growers to seasoned cultivators, the insights and strategies discussed here can empower you to elevate your grow, ensuring that your plants reach their full potential.

Stay tuned for our next instalment, where we'll dive into the complexities of VPD in the flowering stage. 

Happy growing!

FAQs

What is the best VPD for early veg?

The best early veg VPD in cannabis cultivation is around at the lower end of the 0.7 to 1.0 kPa scale. A lower VPD is ideal for young cannabis plants as it encourages healthy transpiration and nutrient uptake, leading to strong and healthy growth during this crucial early stage of development.

What is the best humidity for vegging?

For vegging cannabis plants, the best humidity level is between 65% and 85%. This range supports healthy growth and development by maintaining an ideal environment for leaf transpiration and taking up nutrients.

Keeping humidity within this range helps ensure your plants stay vigorous and ready for the flowering stage.

Does VPD increase yield?

Yes, managing vapour pressure deficit VPD properly can increase yield in cannabis cultivation. 

Keeping VPD within the ideal range ensures plants transpire effectively, improving water and nutrient uptake. This leads to healthier, more vigorous plants and can result in larger, more potent yields.

What happens if VPD is too high?

If the Vapor Pressure Deficit VPD is too high, the air is too dry, which can lead to excessive transpiration.

This makes the plants lose water faster than they can absorb it, leading to dehydration, stress, and potential nutrient imbalances.

Over time, this can slow down growth, reduce yields, and even harm the overall health of the plants. It's crucial to monitor and adjust your grow room's conditions to prevent these issues.

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Tom Starley
March 28, 2024
10 min read

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