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VPD and cannabis: A complete guide

Lucy Starley
September 14, 2023
14 min read
Photo illustating the effects of extremes of vapour pressure deficit on plant health
Photo illustating the effects of extremes of vapour pressure deficit on plant health
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Welcome, cannabis growers, to our comprehensive guide on Vapour Pressure Deficit! If you come across the acronym VPD and wonder, “what does VPD stand for?” then you are about to find out!

As you embark on your journey to cultivating thriving cannabis plants, it’s essential to understand the significance of VPD. It has vital impacts on your crop’s health and yield. In this article, we will delve into the world of VPD. We’ll unravel its mysteries and equip you with the knowledge to optimise VPD levels for your cannabis plants.

VPD is a fundamental concept in horticulture. It plays a crucial role in creating the ideal microclimate for cannabis cultivation. By maintaining appropriate VPD levels, you can effectively manage the transpiration and nutrient uptake of your plants. This leads to healthier growth, improved resin production, and higher yields.

Throughout this guide, we will explain VPD in simple terms. Ensuring that you grasp the concept without feeling overwhelmed. Whether you are a seasoned grower or just starting out, we aim to provide you with actionable insights and practical tips. This knowledge should help you to harness the power of VPD in your cannabis cultivation practices.

But first, let’s demystify VPD. In simple terms, VPD refers to the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold at a specific temperature. Understanding this relationship between humidity and temperature is crucial for maintaining the optimal VPD range for your cannabis plants.

Join us as we explore the ins and outs of Vapour Pressure Deficit. From measurement techniques to the effects of VPD on plant growth. We’ll uncover the strategies to maintain the perfect VPD balance throughout your plants’ growth stages.

By the end of this guide, you will be armed with the knowledge to fine-tune your growing environment. This knowledge will set you on your way to cultivating exceptional cannabis crops.

So, without further ado, let’s dive into the world of Vapour Pressure Deficit. It’s time to unlock the secrets to growing healthy, thriving cannabis plants that will leave you with bountiful harvests.

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.

What is vapour pressure deficit?

Now that we have introduced the concept of Vapour Pressure Deficit (VPD), let’s delve deeper. Let’s explore its workings and understand how it affects cannabis cultivation. By grasping the fundamentals of VPD, you will gain valuable insights into creating the optimal environment for your plant’s growth.

Definition of vapour pressure deficit and its relationship to relative humidity

VPD is defined as the difference between the actual vapour pressure in the air and the saturation vapour pressure at a specific temperature. In simpler terms, it measures the dryness or moisture content of the air. VPD is closely related to relative humidity (RH), but they are not the same thing.

Relative humidity refers to the amount of moisture present in the air relative to the maximum amount of moisture it can hold at a given temperature. On the other hand, VPD takes into account the temperature and calculates the difference between the actual moisture in the air and the maximum moisture it can hold.

To put it in perspective, imagine a scenario where the temperature is relatively high. This would cause increased evaporation and high moisture content in the air.

However, if the relative humidity is also high, it indicates that the air is already saturated with moisture. In this case, the VPD will be low. Conversely, if the relative humidity is low while the temperature remains the same, the VPD will be high as the air has the capacity to hold more moisture.

Vapour pressure deficit affects transpiration

How does VPD affect plant transpiration and nutrient uptake?

Maintaining the appropriate VPD levels is crucial for plant transpiration and nutrient uptake. Transpiration is the process by which plants release water vapour through small openings called stomata on their leaves. It helps in cooling the plant and facilitating the upward movement of water and nutrients from the roots.

Optimal VPD levels create a favourable balance between transpiration and nutrient absorption. When VPD is too high, the air is dry. This causes excessive water loss through transpiration and can stress the plants. Stressed plants can suffer from wilting and nutrient deficiencies.

Conversely, when VPD is too low, indicating high humidity, transpiration decreases, potentially causing stagnant growth and increased susceptibility to diseases.

What is the ideal vapour pressure deficit?

Now that we have VPD explained, let’s move onto what you want to aim for in terms of VPD ranges. The ideal VPD range for cannabis cultivation varies depending on the growth stage of your plants.

Clones and seedlings

As these are baby plants, their root systems have not yet had a chance to develop and become robust.  It’s important to protect clones and seedlings from stress and extreme conditions as much as you can.

Their underdeveloped root systems make it much harder to draw water and nutrients efficiently up through the plant. This is why it is recommended to maintain a low and consistent VPD

Young plants can easily lose moisture from their leaves. As they struggle to replace this moisture, it can lead to stress.

The lower VPD (higher humidity) throughout this growth stage will help to slow the transpiration rate and keep your plants hydrated. The best VPD for seedlings is shown in the table below. It would also be a good idea to consult a specific VPD chart for seedlings.

Vegetative stage

Once your plants enter this stage, they are gaining strength, and their root systems are much more established. This means that the humidity of your grow room can begin to be lowered to start increasing the VPD. This results in faster transpiration now that your plants are able to draw water more efficiently.  The best VPD for veg plants is shown in the table below. But you can also use a specialised VPD chart for veg plants to get a precise VPD level.

Flowering stage

By this stage, your plants should hopefully be exhibiting lots of leaves, and their root system should be robust. This means that your plants are ready to withstand higher VPD.

Raising the VPD in this stage allows your plants to draw up optimum levels of nutrients. It’s also worth remembering that a drier atmosphere is best for preventing powdery mildew and mould. Both are things you definitely want to protect your flowers from.

Please see the table below for the best VPD for flowering plants. Alternatively, use a VPD chart for flowering cannabis plants to further determine the ideal VPD.

Optimal VPD ranges for different stages of cannabis growth

So let’s reveal what the optimum VPD ranges are for each growth stage:

It is worth noting that the specific VPD values within these ranges may vary. The cannabis strain, environmental conditions, and other factors can have an effect. Therefore, monitoring and fine-tuning the VPD levels based on the response of your plants is essential to achieve optimal results.

Factors influencing VPD, such as temperature and leaf surface area

Several factors influence VPD, and understanding them will aid you in managing VPD effectively. Temperature plays a significant role in determining VPD levels. As temperature increases, the air’s capacity to hold moisture also increases, leading to a higher VPD. Similarly, lower temperatures result in a lower VPD as the air’s moisture-holding capacity decreases.

Leaf surface area is another factor to consider. The larger the leaf surface area, the more water the plant can transpire, influencing VPD. Additionally, factors like humidity control, air movement, and plant density can also impact VPD levels.

By understanding these influential factors, you can make informed decisions. You can feel more confident to adjust your cultivation environment to optimise VPD for the best results. In the next section, we will explore the methods for measuring Vapour Pressure Deficit. We’ll also discuss the recommended tools and devices for accurate VPD measurement.

Picture showing a hygrometer measuring temp and humidity

Measuring vapour pressure deficit

Accurate measurement of VPD is crucial for effective VPD management. Fortunately, there are several methods and tools available to help you monitor and adjust VPD levels in your cannabis cultivation environment.

Methods for measuring vapour pressure deficit: using temperature and relative humidity

One common method for measuring VPD involves using temperature and relative humidity readings. By obtaining these two parameters, you can calculate the VPD value using a VPD chart. Alternatively, there are online calculators specifically designed for this purpose.

To measure temperature, you can use a digital thermometer or a temperature sensor. Place the sensor at the desired location within your grow area, ensuring it accurately reflects the temperature experienced by your plants.

Relative humidity can be measured using a hygrometer or a digital humidity sensor. Alternatively, you could use our Grow Sensor, which measures both temperature and humidity, among many other environmental conditions. These devices provide real-time readings of the moisture content in the air. Place the humidity sensor at the same level as your plants’ canopy to obtain accurate readings.

Recommended tools and devices for accurate VPD measurement

To simplify the process of VPD measurement, there are specialised tools and devices available in the market. One popular device is a VPD calculator, which combines temperature and humidity readings to provide instant VPD values. These calculators are often compact, user-friendly, and can be easily carried around your cultivation area.

You can also use cannabis VPD charts. VPD charts for cannabis offer a visual explanation of the relationship between relative humidity and temperature.

To help you with this, we have set out to build the best VPD chart and calculator tool. But we didn’t stop there…

Some environmental controllers or monitoring systems (like the Grow Sensor) offer built-in VPD calculation features. These systems allow you to monitor VPD levels alongside other important environmental parameters, providing a comprehensive overview of your growing conditions.

When selecting tools or devices for VPD measurement, ensure they are calibrated and accurate to obtain reliable readings. Regular calibration and maintenance are necessary to ensure the continued accuracy of your equipment.

Interpreting VPD readings and adjusting environmental conditions accordingly

Once you have measured VPD, it is essential to interpret the readings. Following this, you should make necessary adjustments to maintain optimal VPD levels for your cannabis plants. VPD charts can serve as valuable references, indicating the recommended VPD ranges for different growth stages.

If the VPD reading is too low, the air is too humid. You may need to increase air circulation or implement dehumidification methods to lower relative humidity.

On the other hand, if the VPD reading is too high, it indicates dry air. Increase humidity through methods such as humidifiers or adjusting irrigation practices. This can help bring VPD into the desired range.

It is important to note that VPD is not a static value but changes throughout the day and night cycle. Monitoring VPD at different times can provide insights into fluctuations and help you fine-tune environmental conditions accordingly.

Accurately measuring and understanding the readings helps you to maintain an optimal VPD range throughout your cannabis plants’ growth stages. This will promote healthy transpiration, nutrient uptake, and overall growth.

In the next section, we will explore the effects of Vapour Pressure Deficit on cannabis plants. We will shed light on how VPD influences various aspects of plant physiology.

The effects of vapour pressure deficit on cannabis plants

Understanding the effects of Vapour Pressure Deficit (VPD) on cannabis plants is crucial for achieving optimal growth and maximising yields. VPD directly influences various physiological processes within the plant, shaping its overall health and development. Let’s explore these effects in more detail.

VPD’s impact on plant growth, development, and yield

Maintaining an appropriate VPD range is key to promoting robust growth and development in cannabis plants. When VPD is within the optimal range, it creates an environment that encourages transpiration and nutrient uptake. This facilitates the delivery of water and essential minerals to different parts of the plant. In turn, this supports vigorous growth, healthy root development, and overall plant vitality.

Moreover, VPD has a significant impact on flower production and yield. By carefully managing VPD during the flowering stage, you can enhance resin production, terpene development, and cannabinoid synthesis. Ultimately, this leads to higher-quality buds with increased potency.

How VPD influences stomatal conductance and photosynthesis

Stomata, tiny openings on the surface of leaves, play a crucial role in regulating gas exchange within the plant. VPD has a direct influence on stomatal conductance, which refers to the opening and closing of stomata. When VPD is within the optimal range, stomata open to facilitate the exchange of carbon dioxide (CO2) for oxygen (O2). This enables efficient photosynthesis.

Proper photosynthesis, driven by optimal VPD, is vital for healthy plant growth. During photosynthesis, plants convert light energy into chemical energy, producing sugars that fuel their growth and development. By maintaining an ideal VPD, you can ensure optimal CO2 uptake and maximise photosynthetic efficiency. This leads to robust plant growth and increased yields.

Potential risks of high or low VPD levels

Both high and low VPD levels can pose risks to cannabis plants and their overall health.

Risks of high VPD:

High VPD, typically associated with dry air conditions, can lead to excessive transpiration and water loss from the plant. This can result in wilting, leaf curling, and a higher risk of nutrient deficiencies. Additionally, high VPD may cause stress to the plant. This can impair its ability to recover from environmental challenges and even contribute to stunted growth.

Risks of low VPD:

Low VPD, usually accompanied by high humidity, can restrict transpiration and nutrient uptake in cannabis plants. This can result in reduced nutrient mobility, decreased water uptake, and compromised plant health. Low VPD environments can also create favourable conditions for the development of fungal diseases as the excess moisture promotes their growth. An example of this is the development of powdery mildew.

Balancing VPD within the optimal range is crucial for mitigating these risks.

By understanding the effects of Vapour Pressure Deficit on cannabis plants, you can make informed decisions. You can then implement appropriate strategies to maintain optimal VPD levels. In the next section, we will explore practical tips and techniques for effectively managing VPD in your cultivation environment.

Avoid extremes of vapour pressure deficit for optimal plant health

Maintaining optimal vapour pressure deficit

Achieving and maintaining the optimal Vapour Pressure Deficit (VPD) range is essential for cultivating healthy and thriving cannabis plants. In this section, we will explore strategies and techniques to help you manage VPD effectively. We’ll cover the different growth stages of your plants and how VPD relates to these.

Adjusting temperature and humidity levels to optimise VPD

Temperature and humidity are key factors in VPD management. Consider the following guidelines to optimise VPD by adjusting these parameters:

Temperature:

During the vegetative stage, maintain a temperature range of around 24-28°C (75-82°F) to support active growth.

In the flowering stage, aim for a slightly lower temperature range of around 20-26°C (68-79°F) to promote resin production and enhance terpene development.

Humidity:

During the vegetative stage, maintain a relative humidity (RH) range of around 50-70% to ensure adequate moisture for growth without excessive humidity that may promote disease.

In the flowering stage, gradually lower the RH to around 40-50% to minimise the risk of bud rot and encourage resin production.

Role of ventilation and air circulation in VPD management

Proper ventilation and air circulation play a vital role in maintaining optimal VPD levels. Consider the following practices:

Air Exchange:

Ensure a regular exchange of air within your cultivation space by using exhaust fans or ventilation systems. This helps remove stale air and replenish it with fresh air, maintaining appropriate VPD conditions.

Air Circulation:

Use fans strategically to create gentle airflow around your plants. This promotes transpiration, helps prevent stagnant pockets of air, and ensures consistent VPD throughout the growing area.

Importance of monitoring VPD throughout the day and night  cycle

VPD levels can vary throughout the day and night cycle due to temperature and humidity fluctuations. Managing VPD during the daytime is most important, but its worth considering how you manage through the night too.

The lack of light available during the night causes plants to close their stomata. The closure of the stomata stops the moisture escaping from the plant and therefore reduces transpiration.

Closed stomata also cause photosynthesis to stop. Instead, plants begin to respire, and this converts stored sugars into energy. In turn, this means that plants produce CO2 during the night.

This CO2 still needs to be released by the plant. So it’s important to keep night-time VPD ranges as close to daytime ranges as possible.

Regular monitoring of VPD at different times can provide insights into these changes. This can help you make necessary adjustments to maintain optimal conditions. Consider taking VPD readings multiple times during the day to ensure consistent VPD management.

By implementing these strategies and techniques, you can effectively maintain optimal VPD levels for your cannabis plants. This will support their growth, development, and overall health.

In the next section, we will provide practical tips for Vapour Pressure Deficit control. We’ll also share additional insights to help you fine-tune your VPD management practices.

Practical tips for vapour pressure deficit control

Managing Vapor Pressure Deficit (VPD) effectively requires attention to detail and the implementation of practical techniques. In this section, we will provide you with valuable tips to refine your VPD control and optimise your cannabis cultivation practices.

Providing adequate watering and irrigation

Proper watering techniques:

Maintain a consistent watering schedule, allowing the substrate to dry out slightly between waterings. This helps maintain an optimal VPD range by preventing excessive humidity around the roots.

Irrigation systems:

Consider using irrigation systems that deliver water directly to the root zone, such as drip irrigation or hydroponic systems. These methods minimise foliar moisture and reduce the risk of high humidity, promoting optimal VPD levels.

Using fans and ventilation systems to regulate temperature and humidity

Oscillating Fans:

Position oscillating fans strategically to create gentle airflow across the canopy. This helps maintain consistent temperature and humidity levels, and promotes transpiration, aiding in VPD control.

Ventilation Systems:

Install exhaust fans and intake vents to ensure proper air exchange within the cultivation space. This helps regulate temperature, humidity, and VPD levels by removing excess heat and moisture.

Importance of data logging and automation for VPD management

Data logging:

Utilise data logging systems to track environmental parameters such as temperature, humidity, and VPD. Regularly review the collected data to identify patterns, trends, and any deviations from the desired VPD range. The Grow Sensor app can take on all the measuring and analysing of VPD, meaning you have more time and headspace.

Automation:

Consider automating environmental controls to maintain consistent VPD levels. Using controllers or smart systems, you can program and monitor temperature, humidity, and ventilation. This ensures optimal VPD conditions throughout the day and night.

Common mistakes to avoid when managing VPD in cannabis cultivation

Overlooking plant-specific requirements:

Different cannabis strains may have varying VPD preferences. Understand the specific requirements of the strains you are growing and adjust VPD management accordingly.

Neglecting environmental monitoring:

Regularly monitor temperature, humidity, and VPD levels using reliable devices to ensure accurate readings. Failure to monitor these parameters may lead to incorrect VPD assessments and improper adjustments.

Inconsistent VPD management:

Maintain consistent VPD levels throughout the growth stages to provide a stable environment for your plants. Sudden fluctuations in VPD can cause stress and affect plant health.

By implementing these practical tips, you can refine your Vapor Pressure Deficit management techniques. This enables you to create an optimal growing environment for your cannabis plants. Remember to regularly assess and adjust your practices based on the specific needs and responses of your plants.

Conclusion

Congratulations, cannabis growers, on completing our comprehensive guide on Vapour Pressure Deficit (VPD) and its significance in cannabis cultivation! We delved into the world of VPD. Hopefully, you now have an understanding of its effects on plant growth and development. You should feel equipped with valuable knowledge to optimise your cultivation practices.

Throughout this journey, we explored the definition of VPD and its relationship to relative humidity. We discovered how VPD influences plant transpiration, nutrient uptake, stomatal conductance, and photosynthesis. By maintaining the optimal VPD range for different growth stages, you can promote vigorous growth. You can also improve resin production and ultimately maximise your yields.

We discussed methods for measuring VPD. These included using temperature and relative humidity readings and highlighted the importance of accurate measurement tools and devices. Interpreting VPD readings and adjusting environmental conditions accordingly allows you to create an ideal microclimate for your cannabis plants.

Moreover, we highlighted practical strategies. These include adjusting temperature and humidity levels, utilising ventilation and air circulation, and the benefits of data logging and automation. By implementing these techniques, you can effectively manage VPD and ensure consistent, optimal conditions for your plants’ growth and development.

Now it’s your turn to take action! We encourage you to apply the knowledge you have gained, experiment with VPD management techniques, and fine-tune your cultivation practices. Monitor your plants closely. Make adjustments based on their specific needs, and keep striving for the optimal VPD range throughout each growth stage.

Remember, VPD is a dynamic parameter that can vary throughout the day and night cycle, so continuous monitoring is essential. Embrace the journey of VPD optimisation and don’t hesitate to join communities of fellow cannabis growers. It’s there that you can exchange experiences, learn from one another, and further enhance your skills.

Thank you for embarking on this VPD exploration with us. We wish you abundant harvests, exceptional quality, and continued success in your cannabis cultivation endeavours. Happy growing!

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Lucy Starley
September 14, 2023
14 min read

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